Fish Stress - (primer) Must Read

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  1. jhnrb

    jhnrb

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    EXCERT FROM MARINE DEPOT

    If your fish could talk, they would tell you whenever they were ill or something was bothering them. You could forget about test kits. The fish would let you know when the ammonia level was a little high or the water temperature was too cool. When they needed a change in diet, they could ask for their favorite foods. They could also tell you right away if they had ich or not, and no more guessing which fish is the fin nipper.

    Those of us that cannot ask our aquatic friends "where does it hurt" must depend upon less obvious clues as indicators of our animal's health and well-being. Are fish capable of communicating the status of their health and the stress level of their environment? The simple answer is yes, but distinguishing those signals is a much more complex matter. We can't train our fish to talk, but we can teach ourselves to recognize the behavioral indicators of stress.

    The bad news is, it is easier to recognize behavioral changes than it is to distinguish the disease or stressful condition that is causing them. The good news is that in many cases the corrective action for many of the challenges to our fish's well being is the same. For instance, a water change may alleviate the problem whether a low pH or high nitrates cause it. Another example is reducing the water temperature may be helpful for thermal stress or low oxygen levels.

    Stress causes physical, chemical and behavioral changes in fish. Here we will focus on behavioral changes that hobbyists can learn to watch for and be aware of. Stress can cause fish to exhibit behaviors, cease behaviors or modify the degree to which these behaviors are exhibited.

    Before we can understand how stress effects fish, we must first have some definition of stress and what causes it. What then is stress and can it easily be defined? Stress is an exquisitely complicated subject and even agreeing on a definition can be difficult. For our purposes, we will consider the following definition. Stress is the physiological, biochemical and behavioral response to a stimulus in an attempt to adapt to that stimulus.

    The stress response was intended to be adaptive in nature, so stress in and of itself is not a bad thing. It helps fish to evade predators, respond to challenges and move to locations where living conditions are optimal.

    It is only when fish are exposed to a stressor on a continuous or frequent basis that these responses can become maladaptive. In the confines of an aquarium, fish have little chance of avoiding stressors. One example of stress is when a predator is detected. When the fish senses the presence of this stressor it releases epinephrine and norepinephrine hormones (stress hormones) into the blood stream as a biochemical response. This biochemical response induces physiological and behavioral changes. The physiological changes that occur with the release of stress hormones give the fish a boost in energy with increases in the heart rate, blood sugar, respiration, oxygen uptake and blood flow to the gills. This prepares the fish to better deal with threats to safety or territory in what is called a "fight or flight" response. In this case, the fish is better able to avoid the stressor (predator).

    In our example, the fish survives by eluding the predator. After this episode or challenge, the fish will then seek shelter (behavioral change). Following our example, this fish must regain normal homeostasis. Hydromineral disturbance in inherent to stress in fish. During the recovery period, behavior is modified and the activities of feeding, aggression and swimming are altered.

    If this same animal was unable to avoid the predator, but did successfully evade the capture and was continually challenged, this stress would then become maladaptive. The fish would become exhausted, thereby effecting its ability to avoid predation. Osmoregulation would become increasingly difficult. It would not get enough to eat and the digestive processes would become less efficient. Reproductive behaviors would cease and growth would be minimized. Immune function would be suppressed, making the fish prone to infection and disease. Now the normal stress reaction is working against the animal's survival rather than helping it.

    Stress can be either acute or chronic in nature. Stressors that induce a "flight or fight" response are considered acute. All others are chronic stressors, although some stressors can be chronic and/or acute depending on the situation. Example: stray voltage may be painful inducing a "flight or fight" response. A lower level of stray electrical voltage may only be an irritant causing chronic stress. In general, acute stress is short in duration and chronic stress can go on indefinitely. However, the line between acute and chronic stress can certainly become blurred. Acute stressors include handling or netting, photo or electrical shock, transport, aggression, noise and vibration. Chronic stressors include low dissolved oxygen, inappropriate temperature, low pH, improper hardness, chemicals, rapid or extreme changes in salinity, hunger, heavy metals, pathogens, high dissolved organics, photostress, toxins, confinement, high suspended solids, turbidity and crowding.

    These stressors can be classified into four loosely fitting categories: human interference, extreme changes in the physical environment, water pollution and animal interactions. Some stressors can be placed simultaneously into the more than one category.

    Stress caused by human interference can include crowding, photostress, toxins, electrical shock, transport, handling, hunger or malnutrition, noise or vibration and netting. Extreme changes in the physical environment include sudden changes in temperature or salinity, photostress, excessive water velocity, high carbon dioxide, low dissolved oxygen levels, improper hardness, turbidity, gas supersaturation and low pH. Water pollution includes: chemicals, high ammonia, nitrite, or nitrate levels, heavy metals, a high dissolved organic level and a high suspended solids level. Animal interactions refer to aggression, injury, hunger or nutritional problems (related to aggressive behavior), and pathogens.

    What behavioral changes should we watch for? Basically, look for anything that is out of the norm for your fish. Hiding behind a rock from time to time is normal for many species, but unusual behavior for others. Know your fish and how they typically behave. If you see anything out of the ordinary, then you should observe each individual specimen in the aquarium carefully. Is a fish that normally has a voracious appetite just not eating as much as usual? Are fish that normally stay near the bottom of the aquarium swimming near the surface or a water outlet? Do you see them scratching or hiding more than usual? Are their colors faded?

    Avoidance is a natural behavior response that can be expected when fish detect any type of stressor. This is often the first behavioral modification seen by fish that are challenged by a stressor in the wild. Because of confined space, this can be difficult to detect in an aquarium setting. With the exception of low dissolved oxygen and nutritional deficiencies, all stressors can cause fish to seek shelter or hide. All but nutritional deficiencies can probably cause increased ventilation rates. Any stressor (other than hunger) can cause reduced feeding or lack of appetite. The same can be said about reduced or increased schooling, aggression and swimming activity. Jumping or scratching can be caused by pathogens such as ich (Cryptocaryon irritans), toxins, handling, electrical charges, or transport.

    (CONT)
     
    jhnrb, Sep 4, 2006
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  2. jhnrb

    jhnrb

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    (CONT)

    Toxins, a low oxygen level, pathogens (disease), heavy metals, nitrogenous waste, thermal stress, or low pH can cause abnormal swimming patterns. These patterns can take the form of staying on the bottom of the aquarium, swimming in a figure eight (I call this the death loop), hovering near the surface of the water, or swimming into the water flow of a pump or filter. This can also include changes in schooling behavior. Changes in aggressive behaviors can be induced by crowding, pathogens, photostress, electrical charge, nitrogenous waste, or indirectly by nutritional deficiencies. Handling, or anything that frightens fish will cause avoidance, shelter seeking, increased ventilation rate, decreased feeding and swimming, and increased or decreased schooling behavior. Slowly fading colors can indicate that something is missing from the diet. This is often a lack of highly unsaturated fatty acids (HUFA). When fish become pale over a short period of time (minutes, hours, or days) this is a good indicator that at least one stressor is present. Any number of stressors can cause this. Some fish exhibit brighter coloration when they are the dominant fish in an aquarium or among their own species. Conversely, fish that rank low in the dominance hierarchy can display a pale coloration as a form of submission.

    Stressors are those factors that cause a stress reaction. Some stressors that may induce behavioral changes are:

    Crowding
    Low dissolved oxygen levels
    High carbon dioxide levels
    Photo-stress
    Thermal stress
    Pathogens
    Heavy metals
    Toxins
    Handling
    Electrical charges
    Aggression by other fish
    Nitrogenous waste
    Excessive water velocity
    Noise or vibration
    Low pH
    Transport stress
    Nutritional deficiencies
    Injury
    Improper hardness

    O.K., so fish don't talk, but they can put us on alert to potential trouble by exhibiting changes in behavior. The careful observer can discern these behavioral changes as a signal that something may be amiss. Keep a large batch of water ready at all times for an emergency water change. Test the water parameters on a regular basis and keep a record of the results. Research each species' dietary, and habitat requirements prior to purchase. Have a stock of medications handy for treating the more common fish diseases. Learn how to effectively treat common aliments or diseases. Maintain a separate quarantine to isolate or treat ill animals. Most importantly, observe each specimen daily so that you can easily spot any change in their behaviors early and keep a "heads up" approach to their condition.

    Terry Bartelme is a veteran of over thirty years experience with marine aquariums. He has authored more than one-hundred articles for various aquarium magazines including Advanced Aquarists Online, Freshwater and Marine Aquarium, Tropical Fish Hobbyist and other publications.

    END.
     
    jhnrb, Sep 4, 2006
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