| FISH DISEASES (very long multible articles) | Posted by : jhnrb |
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Diseases of Fish A general overview. Part 1 by Shawn Prescott -Fish in the environment, stress, & more. This column, will try and concentrate on the practical considerations relating to the health of your fish, in the real world of aquarium keeping. Although one may think otherwise, the problems that we face as aquarists, are not exactly the same, as similar fish will face in their natural habitat, although the actual parasites, bacteria, etc. will in so many cases be those, that do sometimes create problems in the wild. Similarly, in the ever growing field of Aquaculture , there are differences, between this method of keeping fish and maintaining them in the average aquarium. Only by being aware of these differences, and the distinct possibilities that each form can manifest in possible problems , can we begin to both understand the potential difficulties, and take sensible steps to minimize the kinds of diseases or problems that may arise, or hopefully avoid them altogether. -Fish disease in the Natural state. The first and major difference between fish in Aquaculture, and the same fish living in Nature, is the sheer volume of water that each fish has access to. This means that although many fish can asymptomatically harbour a parasite, for extended periods e.g. subepithelially , when the parasite is stimulated into a reproductive mode, which typically results in it multiplying itself by hundreds or even thousands of times, the chances of each new spore or Trophont etc, finding a new host, in the wild, is many hundreds of times less , than in an Aquarium or an Aquaculture situation. Even when we allow that typically about half the species of fish shoal , the bodies of water are so large, & other forms of predation so prevalent, that only a minute percentage of the parasites, new spores etc, will have the chance to re-infect another fish. In large part the same logic applies to bacterial & viral diseases in Nature, However, when man or natural events interfere with the Lakes or Rivers, or the Reef environment, which is unfortunately in contemporary times an everyday event, we hear concomitant reports of fish kills with alarming frequency. The corelation to ecological damage cannot br refuted. Pathogenic bacteria are everywhere. When we are healthy, your natural body resistance keeps these pathogens at bay. However if for any reason we become weakened, for example by , exposure to excessive cold, or damp sleeping conditions, these same pathogens often flare up, causing us to become mildly or even seriously ill. Similar consequences can happen to fish in their home of rivers, lakes, and oceans. In Nature when any of the normal background parameters, e.g. temperature of the water, pH, alkalinity, purity ( freedom from pollutants), oxygen values, & more are suddenly changed, from the preferred habitat in which the fish has evolved over eons of time, then the same background pathogens, or parasites, will become very active as the fishes immune system becomes weakened, & unable to provide the amount of suppression to keep these undesirable forms in check. This weakened condition and lowered resistance to disease results from environmental stress. -Stress : The single greatest cause of fish disease. Thus a result of environmental stress large numbers of fish are lost as fish kills in rivers, lakes, and other natural bodies of water , & most of you will have read about same in your local press, or even seen it at first hand. Today this happens with monotonous regularity. In Nature when the prevailing conditions are ideal , only the occasional fish, usually an older one, will become ill. Natural selection usually takes care of such fish, as they are less able to avoid becoming food, for the predators that are omnipresent. This is part of Nature's checks & balances. These weakest had they survived, may have passed on infections to their peer group, but by this process of Natural elimination, this ecobalance keeps down the pool of infection potential, to manageable proportions. For this survival of the fittest rule applies to the entire natural world, and has the practical effect to ensure that only healthy or relatively robust fish survive to reproduce their kind, or sometimes be captured for the benefit of man, either as food, or as Aquarium specimens. Later in these articles I will compare the drastic changes that take place, both before we ever see the fish, and after it reaches it's new home. All scuba divers who have the interest and understanding of ecology, report it is rare indeed, to find fish in Nature showing disease signs, such as we often observe in the Aquarium. Although essentially fish in the wild have a built in awareness of possible dangers, they are also relatively calm, most of the time because they have either many of their own kind around them, as well as a normal habitat . These factors prevent the kind of stress related adrenalin surge , which is the precursor to a weakening of their immune system , in the Aquarium. All to often they have either none, or only one or two of their own kind. Alternatively sometimes in the case of fish that are natural loners, we place 2 of them in an Aquarium, and they display aggression or worse to each other. Either of these unnatural conditions can cause tremendous stress. The ability to recreate a environmental conditions which minimize stress is of vital importance in maintaining good fish health. Furthermore, in Nature fish have typically available to them , a large range of organisms, to serve as food, or at the least such organisms as they have evolved to find suitable, as a complete food for their growth, reproduction and good health. Compare this to the typical diet we give in an Aquarium, which has on average some 10 or more different species of fish, each of which in nature will predate upon different organisms to grow and become healthy, & we feed them one size fits all the same packet of food, day in & day out, with little regard to their individual requirements. Is it any wonder that the combination of these factors result in high levels of stress ? This, given other factors to be discussed, can & does result in the fatal outbreaks of disease that are the cause of so many Aquarists eventually giving up the art of successful Aquarium keeping. (Part-1 cont) ________________ posted jhnrb |
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| Cont. Part-1 | Posted by : jhnrb |
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-Natural Normality , in Nature. Although this may appear to be a redundant play on words, it is worth emphasizing that in the natural , the photoperiod is natural. When the sun comes up it gets light. In Spring, when most fish start to sexually mature it is in response to the natural increase in photoperiod, & with the accompanying rise in temperature in many parts of the world. When dawn arrives it is a slow process, & the same at dusk. The salient point is that any subtle changes in the quality of the water, is usually caused by other natural changes, e.g. such as the rush of melting snows, which can bring about a normal and useful stimuli to the fish Compare this to what is typical in the Aquarium. We configure the lighting to come on at times often to suit our preferred observation times. It is most typically the same all year round, and bears no relationship in many cases, to what is the natural day for the fish. The light comes on suddenly usually within a few seconds, the same when it goes off. Temperature is controlled by clever thermostats, which keep the water, at what our books & specialists advise us, the same number of degrees from Jan-Dec. No diurnal change as happens however modestly even in the Tropics. In Nature in Rivers, in most Lakes, and on the Oceans, moving water, renewed constantly, changed & buffeted by wind, rain, tide, & run off from the mountains, keeps a constant purification going. This helps to overcome the natural pollution which would otherwise occur. Furthermore the myriad of natural organisms, utilize so much of the biota that is created along with the excretory products of the Fauna, so as to ecologically prevent in most cases, any excess becoming a cause of fatality to the world surrounding any one species. Compare this to the typical Aquarium. Some of us do change a percentage of the water in the Aquarium, usually about 10% (if we do) weekly. Many do not even do this. Instead of a natural ecosystem to manage the various subtle changes that are bound to occur, when we keep our specimens in an artificial habitat, we rely upon filters, often changed infrequently, UV's to kill off as much as can, Ozone to purify, chemicals to supplement what we think needs to be replaced, ( the evidence for such replacement is too often questionable). It's rather like asking us to feel good in the rather aseptic environment of a hospital ward. Probably alright, (some today even question that), but it hardly leaves the average person feeling that they would like to go there as they felt so good in that atmosphere. In both freshwater & marine environments there are many forms of natural plant life . Many of these act as part of the food chain either directly for the fish, or indirectly by contributing to other forms of life which eventually are eaten by the fish. I know of no "plastic" forms of plant that exist in nature, but far too many of our Aquarists seem to think that this artificial media, looks nice and is useful. I personally would seek to disagree. Furthermore in many of revered Public Aquariums, I have seen the same plastic rubbish replace the real thing, as evidently the professionals who are employed to run these Mecca's of entertainment are not provided with the means by their money masters, to achieve what should be for so many good reasons an essential educational tool. If one talks "off the record" to many of the Curators of too many Public Aquariums, you may be horrified to hear just how often they have to replace their fish etc. In some cases the record is as bad as Aquarists who have little or no experience. So much for conservation of Nature. Again the reason is in many cases, that to create a stress free environment is one that requires a great deal of expertize, planning & the funds & personnel to make it work, on a long time basis. When this is absent, whether it be in a Public Aquarium or one in our home, then stress is a typical consequence, & fatalities are to be expected, as disease manifest itself. Once again the major reason is the stress factor put upon the fish, which is not in accord with their experience in Nature. Finally in Nature, because as I have said above, natural selection sorts out the weak leaving the best to reproduce, one tends to have stronger specimens. Much more has to be done to both understand, & provide realistic answers to the kinds of problems here outlined, & we will return to this subject later on in the series, in some more detail. END PART-1 Continued.. |
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| Part-2 | Posted by : jhnrb |
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Diseases of Fish: Part 2 by Shawn Prescott (IN PART-1) I attempted to contrast the major differences between fish that live in a "natural state" & those kept by man, either in Aquariums, or in Aquacultural situations. Some may feel that I was in some way against keeping fish for pleasure, and in case there are others who might have felt likewise, I should take this opportunity to say unequivocally, that I have enjoyed keeping Aquarium fish, for almost half a century, and took up what is in fact my profession, because of my abiding interest in them, which has thankfully never waned. It is essential in my view to understand the "norms" of fish in the wild, as a precursor, to being able to take the required steps to minimize the problems of disease that so often break out when fish are kept by man, in Aquariums or otherwise. Later on in this series, I will deal with the specifics of disease, but before doing so, I would like to point out some of the similarities, as well as the major differences, between fish as kept in Aquaculture, & those which we keep in the Aquarium. This with special regard to the influence the differences have upon disease for us Hobbyists. In Aquaculture it is normal to rear just one species in raceways, cages or tanks. Occasionally farmers practice Polyculture ( the keeping of 2 or more species side by side), but this is not common, & even when it is the practice, it is seldom more than 2 species. It is a rare Aquarist that keeps only one or two species, in his or her Aquarium. For the Aquaculturist, this means of course he has a much higher risk if disease should break out, as many pathogens, whether parasitical or bacterial in Nature, often have a preference for a species, which can under circumstances which are favourable then spread very quickly. Contrarily the Aquarium usually has many species which mean that some diseases at least will not spread as fast, and give the Aquarist a chance to get the problem under control. Because of the enhanced risk, good Aquaculture practices, require the fish farmer, to pay constant attention to water quality, disinfection procedures, and the continuous observation of his stock, as any lapse can bring about serious losses, which after all are his livelihood. For this good reason today more and more farms are employing trained Biologists to manage the farms, and try to keep the risk of disease under control. Today many more Aquarists, also pay close attention, but as it is a Hobby and not a source of revenue, for nearly all of us, the degree of close observation & the amount of control equipment is often much less than on a professional farm. Another difference in many but not all farms, is that in cage culture, or such things as Trout culture, in some areas, the water body is constantly changing, taking away pollution, and renewing the quality of the water. There are of course farms that work on closed systems, but even here it is typical to make up some 2% or more of new water daily. This prevents the accumulation of undesirable "metabolites" which are most often Nitrates, Phosphates, Proteins, and more. This cleansing of the water body in Aquaculture is vital, as any diminution of the water quality, can very quickly give rise to stress, which can quickly help bring latent parasites, viruses, or bacteria, into a chronic state of infection. Many Aquarists do of course also change water, many do not do so, or if they do it is infrequent, and anyway, even the best of us, do not do so daily. This means that we must rely on more sophisticated control methods, such as Protein skimmers, Ozone generators, UV purification, Biofilters, and much more in the form of water additives etc. For those of you who have taken the trouble to understand the reasons for such technology, and can measure the effects, this can and does yield some excellent results, such as wonderful Reef Aquariums, as well as beautiful planted fresh water Aquariums. Regretfully, poor advice, sometimes at the dealer level, lack of time, or inadequate understanding of the often quite complex interactions, can lead to heavy losses of fish, and too often to the "retirement" of otherwise keen Hobbyists, who feel that our pastime is too difficult. The purpose of my articles is to try in some small way, to show that this need not be so. You have already heard me refer to STRESS several times as possibly the single greatest cause of fish developing disease, & before proceeding to the more specific details of disease, I would like to give a real example of something that I did with my team some years ago in the UK, which I think emphasizes this point very well. At that time I had an Aquaculture consultancy business in the UK, but also ran our own Labs, & had adjacent to the premises a fairly large Aquarium store. We observed the following phenomena, many times over. Typically we would receive our shipments of fish on a Thursday, so that we would be well stocked for the heavy weekend trade. We had several beautiful show tanks from which we normally never sold, & whenever we got an especially nice specimen, or something that was different we would place this fish in one of the show tanks as an attraction. I would point out that these tanks were set up for long periods of time, were maintained as professionally as possible, as they were our "Advertisement" tanks, and we often did not add a fish for several weeks. I would mention that I am talking about Marines in the example which follows. We made the observation that the following day after adding the "new" fish, that one or more of the "old" fish would have broken out with signs of "white spot" Cryptocaryon irritans, whilst the newly introduced fish was quite all right & showed no signs of any problem. This was contrary at that time to what we somehow expected. Also it occurred so often, that we began to develop a new theory at that time as to the cause. In pursuit of this idea, we decided to sacrifice a fish in one of the tanks which we had had for some 8-9 months, and which was in perfect condition. To this day, I still feel rather guilty about it, as it was a magnificent Powder Blue Tang ( Acanthurus leucosternum). The reason we chose this fish, was that we had had at least 4 examples of this species breaking out previously, with the said white spot. In our Lab, we proceeded to do skin scrapings of the unfortunate fish, and very quickly we found encysted spores of the parasite which were obviously lying dormant and doing no harm. It should be noted that by definition a parasite has a vested interest in its hosts well being, as any change in that status, which may affect the fish, can also have undesirable effects on the parasite. CONTINUED |
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| (cont. Part-2) | Posted by : jhnrb |
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Having proven to our satisfaction the almost ubiquitous presence of this common parasite, we then proceeded to rationalize the outbreaks I referred to as follows:- Fish as most Aquarists have observed are very territorial, they also quickly get to know an Aquarium, and also the other inhabitants, many species will stake out a place of their own, especially Clown fish andother Damsels, but also many others. When a new specimen is introduced, many fish become agitated, they feel that the newcomer, will take their favourite spot in the tank, compete for available food, or "steal away" perhaps their friends. Such alarm can often be seen in school if we can recall when a new and challenging new face appears, especially if he or she is handsome, strong, aggressive, or clever. We manifest this emotion sometimes by feelings of jealousy, or counter aggression, or displays of bravado, which may not even be natural to us. Should there be a major challenge such as occurs many times, when a bully appears, adrenaline courses through our bodies to help us cope with the stress. My team and I, became convinced that something very similar was happening when we introduced the new fish, to those who had "rights of occupation". Some form of chemical messenger undoubtedly ran through the veins of the resident fish, and this would "wake up" the dormant parasite who would translate this message in such a manner as to say to itself, that perhaps my host will not be around much longer, something is the matter, and this STRESS messenger would cause the parasite to immediately go into the reproductive phase and burrow out of the epidermal wall of the resident fish, giving rise to the typical "white spot" markings. Although such a theory is hard to prove, pragmatically we were able to almost do so, as once armed with this conception, we always added the new fish afterwards in subdued light after having changed a couple of hours before some of the rocks in the tanks and other such position markers. We also left the lights out with the tank covered for a day or so. We did not eliminate the problem, but the number of times it happened afterwards was a small fraction of what had been an almost invariable occurrence before our experiment. The lesson to be learned is that many things can cause stress, and that we should always seek to lessen this by understanding the underlying reason, and that if we do, we can greatly minimize the problems that all to often occur. Therefore I hope you will bear with me when as I proceed in this series, you will find I will return frequently to the matter of good husbandry, which is effect the practice of avoidance of stress, as far as the art of Aquarium keeping allows. Some rules which are worth repeating for those who may not know, or have perhaps forgotten or become careless, all of which will reduce stress & therefore the eventual possibility of disease. -When buying fish from your local dealer, try & ensure that the specimen you select, has been in his establishment for a least a week, & see it is feeding. Perhaps pay a deposit on the understanding you may change to another fish, should it not have been there long enough, assuming you really want it. The ask the dealer to keep it a few more days, & ensure you may chose another fish if it does not "measure up" Most good dealers will assist as they want you as a customer. -When taking a fish home, ensure that the clear plastic bag is covered by an opaque cover of some kind. Nothing will scare a fish more than being trapped in a clear bag, from which it cannot escape, & seeing all the strange sights to which it is then subject -Ensure that you equalize the water temperature, as well any pH differences SLOWLY, over at least half an hour, by the slow addition to the bag of the tank water, & floating the bag first to balance the temperatures. Add the fish in as subdued a light as possible, and DO NOT turn on the lights for the rest of the day, to view the fish, which although a natural inclination, should be resisted in the interest of longevity for your new fish, and even the old ones. -Ensure in both fresh & salt tanks, large numbers of hiding places, so that the fish can find a new "home" and feel secure from any perceived enemies. Avoid tapping the glass, to try & bring the newcomer out from any hiding place, when it has adjusted it will display itself to your content. -Ensure if necessary with the advice from your dealer, if the new specimen(s) you are considering, are compatible with those you already have. Some fish are naturally antagonistic to others, whilst in Salt water, two similarly sized Angelfish of the same species will often fight to the death. -Do not overstock the holding capacity of your tank, crowding will induce stress very frequently, & can cause a total wipe out in some circumstances. -If you have burrowing fishes, such as Kuhli loach in fresh water, wrasses or some gobies in salt, ensure that the type of gravel you are using is suitable, as some are sharp & can quickly cause abrasions which will lead rapidly to the demise of the fish, & perhaps spread to others. -Avoid putting on lights in a darkened room, suddenly, as this unnatural shock can cause many fishes to jump out of the tanks, Swordtails are great at doing this. Either only illuminate from a room which is already lit, and if you can try to attach to your lighting system some form of Rheostat control which will bring the lights on and off SLOWLY, just as the sun comes up and goes down in nature. The practice of these basic rules, and no doubt others, will help towards the goal of keeping fish more in harmony, with the natural condition, and this is one as I pointed out last month, that has less virulent diseases, that can occur in Aquaculture & the Aquarium for the reasons I gave . Next I hope to begin the process of looking at the various ways that disease can manifest itself, and begin the long process of trying to understand the many potential problems, and how we can address at least some of them. END PART-2 Continued.... |
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| Part-3 | Posted by : jhnrb |
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Disease: Part 3 By Shawn Prescott Readers will recall that in the last two PARTS, I attempted to show the important contrasts in stress, & therefore the potential for disease between fish as they are in Nature, & those that are kept in captivity, especially those that are kept in Aquariums. Today throughout the world, fish are beening bred in captivity for food in most cases, but also for our Hobby. It is a fact that today, a very large percentage of the fish we enjoy watching in our home Aquaria, have been bred in captivity. This is a far cry, from the early days of the Hobby, when almost 100% of the fish which were sold, came from wild caught supplies, in many countries. Although there are similarities, between the environments in which Aquaculture maintains & breeds its fish, to those we create for the home aquarium, there are also important differences, & in order to better understand, how fish may be stressed & become ill, it is useful to be able to make such comparisons, which are set forth in Table 1. Below:- FISH LIVING IN / IN NATURE / IN AQUACULTURE / IN AQUARIA Many kinds of fish /Yes / No / Varies One type of fish / Never / Usually Almost / never High density / No / Yes / Can vary Ideal water Yes / Mostly / not always / Variable Good husbandry / Not applicable / / Usually Variable Subject to predators /Yes / Only at juvenile stage / Seldom, but can be Natural food / Yes / No / Rarely Water changed often/Yes /Depends on method / Variable Subject to stress/ Yes, but only natural /Stress by crowding & more / Depends upon skill of Aquarist I think it is informative, to look carefully at this short list, as it makes us focus on, what are the similarities, & even more importantly the differences which occur. I maintain that these differences account in quite some measure for the diseases, & the factors that induce our fish to become sick, in too many instances. -Diversity. We see that in the rivers & oceans, that fish are present, in great numbers & in many species. Although predation is a natural form of existence, the various species have evolved methods to deal with it, such as camouflage , shoaling, natural habitats which give shelter, to name only a few, therefore the fish does not feel stressed, as part of its existence, unless exceptional conditions arise. In Aquaculture fish are raised in a number of different ways. These include earthen ponds, cages, raceways, ( of many types of construction), sea cages in open sea, & protected bays, as well as entrapped artificial divergent streams, & Lakes, as well as several other variations of these. For the most part in Aquaculture the fish are the same species, though there is a trend in some areas to Polyculture, ( the rearing of tow or more species, which are compatible, in the same environment). Here at least although stress can & does arise for other reasons, the stress that can be caused by an incorrect choice of species in the Aquarium does not arise. In Aquariums, it is usual to find a few to many kinds of fish, the discerning Aquarist, will ensure their compatibility, but often by wrong advice or being unaware he will put a fish or two, into the Aquarium, which will become very aggressive to others, & will cause stress to other fish, which can quickly result in disease breaking out. -Density. In Nature, the oceans are to a large extent unlimited at least as far as the numbers of fish are concerned. Thus although the numbers in some shoals may be enormous, there is never any problem of overcrowding or the consequential deterioration of the water quality. In Aquaculture, the name of the game, is to get the absolute maximum numbers of fish, per given size of tank, cage , pond or whatever, as is commensurate with rearing the fish to point of sale, without them getting ill. The expert fish farmers, spends much of their effort, in trying to achieve just this. However from time to time for many different reasons, engineering breakdown, storms, changes in water quality, the fish may be & are sometimes subjected to tremendous stress, & when this happens, the window of time to rectify this is short, & limited. In Aquaria, except with those novice Aquarists, whose enthusiasm exceeds their current knowledge, today most Aquariums, are not overcrowded. When this rule of giving reasonable space to the species we intend to keep, & ensuring that we have made due allowance for the eventual size they will become, the question of density causing stress should not be a factor. Remember though, especially newcomers to the Hobby, it can easily become a factor. Thus choose your fish thoughtfully, & with careful research into the compatibility with the fish you already have. (CONT.) |
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| Part-3 (cont) | Posted by : jhnrb |
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-Water quality. In Nature the water quality is for the most part a constant, with a few exceptional conditions, which may be caused by run off, or flooding etc. Here the fish has evolved in its ideal habitat, & it is very rare, for any stress to be caused by water chemistry, or temperature changes, other than those which are natural. However increasingly & most regrettably, there is yearly more reported "Red Tides" & similar type occurrences, which are not fully understood at this time by Science. Much informed opinion leans towards the explanation, in at least a large number of cases, that mankind's alteration of the environment by run-off's , by untreated sewerage, by oil spills, by damming of rivers, & so much more. These "Red Tides", are in many cases, highly lethal, sometimes to the fish themselves, other times to humans who may ingest species exposed to these tides, which often cause toxins of rare potency to be formed. The economic losses, due to the shut down, of collection especially shellfish, during these outbreaks, by Governments, to protect public health, runs into millions of dollars, so assuming that we as humans are in some measure responsible, the consequential losses in economic terms are considerable. In Aquaculture, the water quality, is in many cases, totally controlled by the farmer, although in sea cages, it can be similar to nature, though even here some problems have arisen. Because this vital parameter is so important, in most fish farms, water changing is a part of the everyday routine. Not withstanding this, many are the occasions when some vital chemical or other parameter, will change, invariably for the worse, & this can threaten the stock of the farm, often within a horrifically short period of time, which can amount to less than an hour in extreme cases. In Aquariums we today have the technology to control water quality to a high degree. Notwithstanding this, for a large number of good reasons, the water quality from Aquarist to Aquarist, varies in large degree, form superb, to abysmal . Among the myriad of reasons, are, lack of good advice from the dealer, lack of adequate funds to purchase some of the essential equipment, poor water quality at source, & there are several others. The high quality Aquaria, will encounter a much lower level of diseases, whilst one can be sure, that the lower levels of water quality, will have the highest incidence of disease outbreaks. One can also say with certainty that many of the Aquarists who quit the Hobby, do so because they have lost too many fish due to disease. It will help everyone to be successful, if we can try together to reduce disease, & improve where necessary the water quality. -Good husbandry. In Nature, this matter is not relevant, as the quality of the fishes life is natural, & it will normally thrive. In Aquaculture, this is the essence of what fish farming is all about, & woe betide those farmers, that become careless, or do not keep up with the most successful techniques. Any improvements in technology rapidly spread in today's world, & quickly are reflected in the final price of the fish. For this reason most fish farmers, are constantly tending their stock & pay great attention to their well being. In Aquariums, this is certainly also true for the elite among our Aquarists. I would say, even the majority among those of you reading articles like these. Regrettably this is not always the case among too many of the millions of Hobbyists out there. Lack of time, paucity of knowledge, combined with the fact that for too many, Aquarium keeping has & always will be, a passing fancy, to go along with other whims, like roller skating, baseball, the latest movie, etc. It is here that the quality of the water tends to vary downwards, with all the attendant consequences of disease, & final abandonment by the enthusiast for the Hobby he ardently espoused for a few weeks or months. -Predation. In Nature, fish are constantly predating on other fish, or plankton, algae or whatever. This is part of the natural cycle of life. They in turn, with a few exceptions like large whales & sharks, are also subject to predation. Most fish have a built-in awareness of the dangers, & over eons of time, have evolved techniques to lessen the risk. Among these are shoaling ( safety in numbers). Background camouflage , habitat security, development of toxins to ward of predators, association with other species, that lessens their risk, & more. Because all of this has happened naturally, they are seldom in a heightened state of stress, although they have this consciousness that causes them to take cover, when they think danger may approach. We have all seen shoals of fish, move in sudden uniform fashion, to another direction, which is almost always, an instinctive reaction to a perceived danger, which they hope to avoid. By & large then, stress & its consequential increase in disease factor, is not very high in the natural environment. Aquaculture , for the most part, with good management, is seldom subject to predation, unless in the case of ponds or lakes, etc., there are natural predators that may prey upon the stock. These can & sometimes are a serious nuisance. Among the worst offenders, are Herons, Pelicans, Snakes, Otters, Monitor Lizards, & others. However any serious fish farmer, is aware of these risks, & technology today, is capable in large part of finding answers to this problem . There are still some types of predation that we need to find answers to, & these are the subject of constant & ongoing investigations. One such in Aquaculture especially in Salmon culture is a form of predation that is in reality a parasitic disease. Sea Lice, have emerged as a substantial predator on stocks of salmon, which are now farmed in many countries of the world. These cause enormous economic damage, & although some progress has been made to control them, it is not yet adequate. In Aquariums, predation is often caused by the Aquarist being unaware of the incompatibility of the specimens he has chosen. In Reef tanks many Invertebrates, even though sessile, are capable of causing injury leading to death, of another species, when they are placed to close together so that they touch. Many species of fish will attack another kind, often incessantly, & this with some major & beautiful species of Angelfish, is especially so, when the fish are the same kind & of similar size. Other species like Butterfly fishes will live on their natural food, i.e. certain corals, to the horror of the owner, who has spent hard earned money to acquire a prized specimen. Not only does this cause losses, but the fish which are attacked rapidly develop major stress symptoms, as they unlike in Nature to escape the problem, being confined in an Aquarium. These symptoms are too often the reason that a disease will break out, which then quickly passes, to others in the tank, who although not being attacked cannot escape the spread of the infective organism(s), that ensue. It is therefore vital that when we select species of fish or invertebrates for our Aquarium, we should ensure that we carefully taken note of what is compatible, not only with the new species we are about to buy, but also with those we already have in our tank. (CONT) |
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| Part-3 (cont) | Posted by : jhnrb |
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-Natural food. In Nature, there is only natural food, so this is hardly ever a cause of disease, as each species seeks out the forms of nourishment most suited to its requirements. There is today an increasing danger however that as mankind has "successfully" overfished almost all of the major commercial species, that the "natural" chain of food, now for the first time, having its knock-on effect, may cause some changes in the ability of many species to have an adequate diet. This overfishing effect has already had undesirable results, with much bird life, when their preferred food species has been tremendously diminished , e.g. sand eels on the Puffin population. The environmentalists, must also be allowed to make their studies & inputs into the decisions about fishing quotas, & we have a long way to go, before we can safely say we understand it all. In Canada, the economy of the State of Newfoundland, was seriously impacted when the Government having for years got their statistics wrong, were forced to close down the major fishing grounds on the St. George's bank, with the loss of some 30,000 land based & seafaring jobs. This economic loss is still affecting the local economy. In Aquaculture, natural food is seldom applied. Almost all diets, although invariably containing some fish meal ( a major limitation at the moment on the unbridled expansion of fish farming), are produced in factories that make up a balanced feed, that contains state of the art, know-how about the various requirements of the fishes dietary needs. An interesting but minor exception to this was recently revealed on one of the bulletin boards of the Aquaculture industry. I do not recall if it was Scotland or Ireland, but they contributor found that they were getting a very high conversion ratio, ( less than 1:1, this means that they were getting more food in production of the salmon, than they were feeding to them, on the face of it impossible). On investigation they found that the droppings from the fish were causing a "bloom" of phytoplankton, which attracted vast quantities of mysid shrimp. The salmon fed on these shrimps, & grew at a much higher rate than had ever been observed for the applied ration of food. I feel sure that variations of this may become a part of future fish farming. There has been in Aquaculture, because of the nature of the food, some important & costly disease/problems, among them it has been found, that some manufacturers, did not have adequate quantities of Zinc, in their diets, & this caused blindness with important losses, until rectified. Other diets have been found to lack on or more of the various vitamins, or amino acids, most of which are as vital to the healthy growth of fish, as they are to all other types of living creatures. It is seldom practical to feed natural live foods to the fish in Aquaculture, but it may be pleasing to you as Aquarists to note, that when there are exceptions, it is usually from the ornamental side of the industry, that such are used. Of course in the early larval stages of Aquaculture natural live foods are used all the time, most especially in the form of Brine shrimp( Artemia), without which there would be no Aquaculture as we know it. Aquarium use of live food is highly variable. Most good shops carry one or more varieties of live foods, & a large number of serious Aquarists buy such on a regular basis, & some others, culture or collect their own. The use of such foods is important , & in some cases vital, as there are fish, who will never touch a prepared food, such as leaf fish in Freshwater, Seahorses, & Lion fish in Saltwater & many others. Without such additions to their diet, many fish will progressively weaken & become prone to disease. This can be avoided, by choosing a suitable live food & feeding it regularly, although it is often difficult to ensure without a great deal of trouble, that the fish that need the live fish most, get to it. Too often other faster fish, have eaten all or most of it, while slow moving fish like those mentioned, have had almost none of the same. Another alternative is either to avoid such obligate live feed species altogether, or keep such only in a tank to themselves. Sometimes Hobbyists will do this, & ensure that a number of pregnant female Guppies are always present. Such females will eat almost any food, whilst the continuous supply of offspring will provide a constant live food diet to those that will eat nothing else. Hobbyists should be aware, that Guppies, can be kept in full saltwater, & will even breed, if the "change over" is done gradually over a few days. Whilst large Lion fish, will also eat the parent stock, Seahorses will not look at an adult female, but will eat newly born fry. Aquarists, should take careful stock of their fish, along with the eating habits of same, & ensure that the diet, is adequate & balanced, otherwise over a period, stress will develop, & with it disease that can affect all the fish in the tank. -Water changed often Finally in Nature the water is constantly changing, & only as said earlier if pollution occurs is their any problem on this account. In Aquaculture water is often changed on a regular basis, or if in cages in the ocean, is subject to constant change. Notwithstanding this, from time to time even in the sea, the sheer volume of fish in a given area, has caused some massive problems, & this in various ways. Good fish farmers, are aware of this problem, & today techniques to measure & control the problem are in place in the more important countries. In Aquariums this is a major variable. Most Aquarists are aware they should change the water on a regular basis. For reasons of time, money, "theories" that contradict the popular wisdom, as well as the insistent adverts, of some producers of additives, many change rarely or insufficiently. Without doubt, this factor is responsible for many unexplained "sudden" outbreaks of disease, in tanks that had apparently had no problems. A good rule of thumb, in Aquariums that are NOT overcrowded, is to change about 7-10% of the water volume weekly. This in both fresh or salt water tanks. These then are the major differences between the environmental pressures that fish are subjected to, in the 3 different ways of their existence. By looking carefully at these, & understanding, what helps & what does not, then by applying these principles to our Aquaria, I believe major benefits can result. For those of you, that are fed up with me rambling on, about the background to disease, in part 4 I will begin to examine the various forms that disease can take. Along with the treatment, or preventative action that is sometimes possible end part-3 (CONT) |
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| Part-4 | Posted by : jhnrb |
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Diseases in Fish Part 4 By Shawn Prescott Well finally ( not before time, probably some of you would say), we will begin the long journey to examine the many ailments that fish are prone to. The lists are so extensive that sometimes one wonders how fish survive at all, given the countless "enemies" just waiting to strike them low. Not withstanding this, most fish given good husbandry & attention will thrive & be a constant pleasure to those of us, who like to replicate a small piece of nature in our own homes. The diseases and problems that can afflict fish can be broken down into the following categories:- 1) Parasitic 2) Bacteriological 3) Viral 4) Nutritional 5) Toxicological 6) Environmental 7) Other. we will begin our investigation of diseases, by looking at the first major group, that is the parasitic species, that are endemic to so many of the tropical fish, which for the most part today are bred on farms. -PARASITES OF FISH GENERALLY: In considering these parasites, the Hobbyist should be aware that some parasites essentially need an intermediate host, in order to be able to complete their life cycle. In several cases such an intermediary is a snail, or some form of Invertebrate such as Daphnia, or other similar organisms. In such cases, by eliminating the intermediary we can bring the spread of the infestation to a halt. In the wild probably a majority of fish are host to one or more parasites, but for reasons addressed in previous articles, they seldom become a major problem or cause of mortality. In fact there is considerable evidence that in some of the more prevalent parasites e.g. White spot that exposed fish can develop an immunity against further attack Whilst it most cases it is recommendable for the Hobbyist to purchase young specimens, ( as they will live longer, & more easily adapt to the confines of his/her Aquarium), such specimens are also more prone to succumb to attacks by parasites having less size, and body weight to resist the damage that many of the parasites can so easily inflict. For this reason, any purchases, should be carefully inspected, to ensure that there are no "blemishes" of any kind, on the desired specimen, & the buyer should also ensure that no fish are bought from any tank in which any fish are manifesting unfavourable symptoms. Parasites once present in a tank can in so many instances spread rapidly with devastating effects, & a fish that has been exposed & yet appear to be perfect, can break out within a day or so, spreading its parasites to others in your Aquarium. For those of you that have the possibility , it is advisable to keep all newcomers in a separate quarantine tank, when first purchased. This will give one the chance to ensure that nothing untoward, will be transferred to the principle Aquarium, as it is counterproductive to try treating a fully setup community system, when disease breaks out. The period of such quarantine, bearing in mind the life cycles & latent period of so many of the potential problems should be 3 weeks. This is the period used by Government edict in Australia, which is one of the few countries so far, to require all imports of Tropical fish to be so held, in Government approved holding facilities. Therefore if you do take the prudent step to quarantine all new purchases, it is wise to make certain that they are kept for at least two weeks, if not three, before introducing them to their new home. I realize that such goes to a large extent against the "I want it now" , type of society we live in today, but the " I want a cure, that is 100% effective, works in one day or less , & causes no headaches" DOES NOT EXIST, so caution can pay off in spades, as they say. It is also important to note, that parasitic infestations, often do not kill directly. However because of the damage they cause to the tissues & vital organs of the fish, they frequently cause secondary opportune infections of bacteria & fungi, to invade the fish, bringing about a rapid death of the host, & often spreading the new infection throughout the Aquarium. In order to avoid the potential spread of any infestation or infection, all nets, or utensils of any kind that may used with your fish, should be kept in a sterilizing solution between uses, & rinsed thoroughly before & after use. -Methods of diagnosis: (Parasites) Although it is possible to come to a reasonable diagnosis, by carefully noting observed signs (symptoms or indications), which in fact is part of the purpose of this series of articles, it is most useful if the Aquarist can manage to have on hand the following tools to aid & help confirm their findings. An inexpensive stereo microscope. This should have magnifications of 10-40 times to enable one to observe the majority of the parasites. Such microscopes can be bought new nowadays for around $500, but many are available from secondhand dealers, for about a third of this price. If buying a used instrument ensure that the optics & mechanical system are in good working order prior to commitment. A few glass or plastic Petri dishes of suitable size in which one can lay the fish in a small amount of water whilst making observations. A simple fine pair of tweezers, which can be used to "pick of" some of the larger parasitic forms for closer examination, without keeping the fish too long out of water. Some glass microscope slides for making skin smears. A simple plastic rod (thin about 3mm daimeter) which can be used to gently pry open the gills of the fish for examination. A fine pair of scissors which may be needed to excise a small piece of fin tissue, for closer examination. A glass pipette, which may be used to aspirate (suck), some material from the gills or elsewhere for further examination. Whilst these materials are not essential, they do make accurate diagnosis, far more certain, & any Hobbyist who has invested serious money in their Aquarium(s), would be well advised to try & obtain the above items. -Diagnostic procedures. Whenever fish are observed with some abnormal signs or behaviour pattern, it behoves one without delay to try & make a determination of what is the cause. Even if one suspects that the cause may be parasitical, bacterial, or viral, the first thing that should be observed & noted are ALL the water parameters. Often an adverse change in the quality of the water can induce latent potential infections to break out, so that even with a correct diagnosis it will be extremely difficult to treat the problem without taking steps to remedy the cause of the water in-balance. Some signs such as hanging at the surface, are common to the observed indications for some diseases, but also to water quality problems like Ammonia toxicity. Thus even though we will pursue all the recognized procedures for determining the cause, first ensure that the water parameters are where they should be for the species you are keeping. Poor water quality can bring on many parasitic diseases. Reliable & easy to use test kits should be used to ensure that the quality of the water is in accordance with normal parameters. If for any reason they are not, take the appropriate steps to rectify the problem, ensuring that any correctional changes are made slowly to avoid further stressing the fish. Assuming the water quality is within normal values, then one should proceed as follows:- 1) Note down all external observations that are abnormal. -Behaviour One should examine any signs of abnormal behaviour, such as unusual swimming patterns, refusing all food etc. etc. -Body Look especially for colour changes, bleeding or ulcers, swellings etc. -Skin Try & observe any cuts or lacerations, scales protruding etc. -Eyes, Observe if any Exopthalmia (popeye) is apparent, or cloudiness etc. -Gills Examine the Gills & note if the colour is a normal bright red, or if it shows unusual colour or other markings. -Fins Note if the fins appear normal, or are rotting, or show markings etc. (CONT.) |
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| Part-4 (cont) | Posted by : jhnrb |
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When all the unusual signs have been noted it is then sometimes possible with the aid of a good text book or computer programme, to make a determination . However just as in human and animal medicine, we like to have absolute confirmation, & for this reason some of the verifications which follow should be attempted, this assuming you have the above mentioned equipment. If one does not, then the specific details of each disease, should be kept, as a reference source, along with any other good book that one has, & you make your best shot, at the problem, without the "proofs" which we will now talk about. (ADVANCED AQUARIST) -Skin smears. Probably the easiest & often the one that will "prove" the diagnosis fastest & most conclusively at least as far as parasitic infections are concerned is the skin smear. In order to do this one takes a clean microscope slide & simply presses it gently over the area on the fish that one suspects is a source of the problem. One can also "run" the edge of the slide along the infected area, with a little pressure, & this will almost always release some of the epithelial matter along with some indication in many cases of the causative organism. A word of caution. In a fish that may have had a wound or similar for quite some time, ( over a couple of days), there may already be secondary infections taking place, of a fungal &/or bacterial nature, it is important to be aware of this when taking such a smear, & these are best done in the earliest stages for best results. Once the smear has been made, it should have a drop of clean water should be added to the slide with a pipette & an examination under the microscope should then take place. Be careful when adding the drop of water that only a small amount is added, otherwise the vital material to be examined can all to easily "flow" off the slide & make the examination more difficult or useless. Again a good reference book, or computer programme will be needed for most Hobbyists to enable them to recognize the causative organism which may then be observed. -Fin Biopsy If the fins show any abnormality, one should take the fish, holding it gently but firmly in a wet clean cloth, & using a fine pair of scissors, cut a small piece of tissue from a fin that is showing signs of abnormality. Cut between the fin rays, so that only tissue is removed, in this way minimal damage to the fish will ensue. Proceed to examine the sample in the same way as with skin smears. -Gill examination Hold the fish as mentioned above, & prise open the gill covers with the mentioned clean plastic rod. Insert a fine pipette & aspirate (suck) a small amount of tissue, from the gill lamellae taking from any part that may appear abnormal ( dark in colour, pale, with small black or white dots etc). Let this material drop onto a clean slide as before & proceed to examine same. Wet mount of a Gill Biopsy showing I.mutifiliis trophozoites. Photo courtesy of Dr. Ed. Noga. NCSU. Should one need to proceed to do post mortem examination of a dead fish, then it is advisable to use a qualified laboratory, & take samples from some of the internal organs as well as the outer body. For such examinations detailed methodology which requires some special preservatives, as well as certain specimen holders & more must be used, otherwise the chances of it arriving in a fish disease laboratory in a useable form are remote. Laboratories tell us that nearly half the samples they receive cannot be used as they have not been prepared correctly. Qualified laboratories will instruct persons what procedures must be followed. Armed with your notes on external signs & adding to this confirmatory examinations as indicated it should be possible to make accurate determinations for at least the majority of parasitic infections. In the following articles we will deal with some of the major diseases as are typically found in the Aquarium, beginning with by far the most prevalent. END Part-4 (CONT) |
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| Part-5 | Posted by : jhnrb |
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Diseases in Fish Part 5. Shawn Prescot -Cryptocaryon irritans Causative organism: Ciliated protozoan parasite viz:- Cryptocaryon irritans Synonyms ( alternative names):- Marine white spot. Geographic distribution. World wide. Water type . Salt water. Typical signs of infection. Cryptocaryon irritans. Water. Less than optimum water quality, such as a lowering of the pH level, or high Nitrate or Phosphate readings can lead to an outbreak. Behaviour. Fish will evidence lethargy, and may from time to time, try to "scratch" of the organisms, by rubbing against an object of some kind in the Aquarium. Distress is visibly obvious. Fins. Fins often become clamped or folded. White spots (after which the disease is popularly named) usually appear often at first on the pectoral fins. As infection progresses, very large numbers of these spots of size 0.5-2.0 mm will spread . Body. White spots appear on the body, & will if untreated spread so that almost snow like appearance will spread over its entirety. Some haemorrhaging may appear in later stages of the disease. Eyes. In medium to advanced stages of an outbreak, the eyes typically become clouded, & when very heavy blindness can ensue. Gills. Gill examination will show large numbers of the organisms . Skin. (smear). Should show ciliates once an infection has become established. Secondary infection with fungal is commonplace once major invasion of the skin has taken place, adding to the problem. -Life cycle Transmission is direct, with no intermediate hosts. Cryptocaryon is an obligate parasite, which means that it must infect a host fish in order to complete development. The life cycle of Cryptocaryon can be conveniently divided into four basic stages. Susceptible marine fish become infected with the active free-swimming stage, called the theront (or tomite). The theront is incapable of feeding within the aquatic environment and therefore has a limited time, less than 12 hours, in which to contact and invade a fish, otherwise it will exhaust its energy reserves and die. If invasion is successful, the theront penetrates below the skin epithelium, possibly aided by digestive enzymes such as hyaluronidase, and transforms into the parasitic stage which is known as a trophont. The trophont actively feeds on the fish's tissues, twisting and rotating as it does so. It grows rapidly, doubling in size approximately every 24 hours. By 48 hours, the parasitic trophont is just visible to the naked eye, appearing as a small white spot on the fish. By the third or fourth day of infection, the trophont will have attained 3 to 5 millimetres in length and at about this time it exits from the fish. Although the trophont is equipped with rows of beating cilia it is too bulky to swim away from its host and instead it sediments to the substrate. ( Within a few hours, the trophont has firmly attached to the substrate and rounds up to form a thick-walled cyst. The cyst, also known as a tomont, is the reproductive stage which will eventually give rise to between 100 and 300 infective theronts, thereby completing the life cycle. Of course, not all theronts are successful in locating and infecting a host, even under ideal conditions only about 5-10% succeed. Nevertheless, within an closed environment, Cryptocaryon can increase in numbers by approximately tenfold every six to eight days. This enormous reproductive potential explains the sometimes rapid build-up of infection levels in any closed system.. The cyst is the only stage of Cryptocaryon which is known to reproduce; there is no conclusive evidence to suggest that the parasitic trophont stage can multiply within the fish's epithelium. -Prognosis There is no reason why mortalities should take place, as to reach lethal levels this parasite usually takes some 7-12 days. Observant hobbyists should take remedial action, at an early stage & if this is done, and the results CAREFULLY monitored than a successful eradication of the problem is possible. Care must be taken, to ensure that no latent parasitic tomonts are still present, so that the problem does not recur. -Treatment In those Aquaria, where fish only are present, Copper based remedies, are very effective, although those chelated forms of Copper of which there are several have not in the writers experience given good results. The claim that you can use heavy doses of such Coppers, without harming the fish may be true, regretably the same argument applies to the parasite. With the true Copper treatments that are effective it is vital to use a reliable Copper test kit, & in the first few days of treatment this must be done several times daily, as the Copper in a new tank to be treated, "binds' to the glass the rocks, & just about anything else, so that the theurapeutic level drops below the recommended amount, & under this the parasite is able to complete its life cycle. Treatment should be continued for at least 7 days after all signs are absent, to ensure that no latent tomonts are waiting the chance to reinfect. In Reef Aquaria, however no Copper treatments can be used, as they all will have fatal effects on almost all Inverterbrate life. This leaves the Hobbyist with the alternative of catching his/her fish, & treating in a separate Aquarium. This is time consuming & can often ruin the appearance of a tank that has been carefully nurtured over a long period of time. Fortunately Fish-Vet ® has today a product called Ecolibrium ®, which allows successful treatment of this scourge, and is harmless to all Invertebrates. No test kits are needed & it biodegrades after a week, when treatment is ceased. Another technique which can be used to help accelerate the eradication of the problem, is by giving the fish baths in either fresh water, or at a salinity of less than 10 ppt. The parasite cannot tolerate the change in osmotic pressure, though I am not sure if it will affect the tomite stage as much as it will the free swimming trophont. This technique has been used very successfully in Aquaculture with those species of fish that are highly euryhaline (= able to tolerate wide variations of salinity). Our Aquarium fish for the most part will tolerate baths of up to a half an hour, but one must ensure that the pH & Temperature are similar to the Aquarium water. Also do not do any other task whilst the bath is taking place, as some fish will react worse than others. If major distress is observed, the fish must be returned to the Aquarium. I have used this method to reduce the level of infection, & it has proved beneficial, though never absolute. It's greatest advantage is when the fish shows evidence of a high level of infestation, & one wishes to bring it down somewhat before starting more conventional treatment. There is some evidence that there are 2-3 different strains of Cryptocaryon irritans , nobody to my knowledge has yet made a definitive analysis of such, but the empirical evidence would seem to indicate this. One observation made by many observers, is that the treatment that in one case is quickly and totally successful, in another either is not, or takes much longer to have an effect. One pragmatic point that the writer has used with success is those persistent cases, that either do not appear to react to conventional treatments , or do so much more slowly, is that it seems that the parasite is in some way linked in its life cycle to the photoperiod. In order to disrupt its usual timing of division, reproduction etc, I have found it helpful on occasion to leave the lights on , for some 2 days, & then do the opposite whilst at the same time covering the tank with a dark blanket or suchlike. This "manipulation" of the light seems to have a deleterious effect on the parasite, which coupled with the medication used often results in its elimination. I do not advise this however in the more usual straight forward cases. (CONT) |
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