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
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