Stress and Fish Health
The nature of keeping aquatic species in confined environments generates many stresses that are unique to aquarium fish. To be successful in keeping healthy aquarium fish, you need to know what causes stress in fish as well as how to prevent it. Elevated stress levels are at the root of most health problems in fish and this article will help identify the causes of stress and give recommendations for treatment.
What is stress?
The effect stress has on a fish's health
The causes of stress
Elevated levels of ammonia, nitrite, and nitrate all create deterioration in fish health due to stress. High levels can cause severe stress, whereas slightly elevated levels can contribute to chronic stress.
pH levels that change abruptly cause acute stress and continually elevated or lowered pH levels can cause chronic stress. Many fish adapt to long-term changes, but there are limits. pH changes of more than 1.5 points below or above recommended levels are going to have a negative effect over time and should never be considered acceptable.
Temperature fluctuations are a much underappreciated stressor of fish. Most tropical freshwater and marine fish do not tolerate temperature changes very well. Many tanks that are not set up properly will have over the recommended maximum of one degree of temperature fluctuation in a 24-hour period due to room temperature, lights, and equipment. The daily fluctuations will create chronic stress as will having a too low or too high of a temperature in the tank for the species of fish present.
Wild fish live within very specific salinity levels (levels of salt in the water). Their bodies work hard to maintain the osmotic gradient between themselves and their environment. If their environmental salinity is not specific to their needs and is not held at a steady level, they have to work harder to maintain their osmotic gradient, which generates chronic stress.
Oxygen levels that are below recommended levels can cause fish to 'breathe' faster than optimum and this can result in chronic stress. Obviously, very low oxygen levels can lead to severe short-term stress and death.
Harassment from other fish and lack of hiding spaces go hand in hand. There should be two suitable hiding spaces for every fish in the tank, otherwise, there are going to be fish that are stressed and bullied. Remember that unlike their environment in the wild, these fish are confined and cannot get away from aggressors. Aggression is a very real problem in many tanks that leads to many injuries, infections, and death.
Overstocking of the tank is a common problem that contributes to almost all of the stresses in the above list, from water pollution to oxygen depletion to harassment. Do not overstock your tanks. If you want to stress your fish, put too many in the tank and it will happen every time.
If you add something to the water to treat a disease or water condition, be aware that it can be stressful to your fish. Try to avoid treating the water if at all possible and always use a quarantine or treatment tank. Copper is an excellent treatment for ich or velvet, but it can be toxic and stressful to fish. Of course, using it is much better than letting a fish die from velvet, but it should never be used in a tank with healthy fish.
Improper nutrition is also a commonly overlooked stressor of fish. Many fish can live on minimal nutrition with old or stale flake foods, but this poor nutrition is a chronic stress. A variety of well-preserved dry foods as well as freeze-dried, fresh, and frozen foods specifically designed for individual species are necessary to prevent chronic nutritional stress.
Disturbing the tank through banging on the glass, constantly netting fish, or rearranging décor stresses fish and should be kept to the necessary minimum.
There is probably nothing that stresses fish more than bringing them from the wild or an aquaculture pond through the wholesaler to your home. In just a few days, the fish will be captured, held, packaged, shipped, sorted, handled, packaged again, and so on through the collector, exporter, importer, wholesaler, and retailer to your tank. Throughout this process they may be exposed to drastic changes in temperature, ammonia, pH, salinity, diet, medications etc. They often do not eat and arrive at your tank completely stressed. If they are not handled very carefully and are not placed in an optimum environment, their stress is going to continue and they will get sick and die. The reason that this stress is listed last is not because it is the least important, but because it is the most significant. You need to understand all the stress factors and how to eliminate them because these fish that arrive at your tank have been exposed to all of the listed stresses. The unfortunate truth is that the majority of fish mortalities occur at or near the time of entering a new tank and only through an appreciation of stress and its effect on fish can this problem be prevented.
How you eliminate stress
Stress is one of the most critical factors in fish health. Only by understanding the effects that stress has on fish, as well as being able to identify and prevent common stresses, can we eliminate this problem. As aquarists, we need to be responsible for the health and welfare of all of our fish. Provide the highest quality water, nutrition, and suitable tank environment. Introduce new fish carefully and always use a quarantine or treatment tank when necessary. If we work hard to reduce the stress in our fish, we can virtually eliminate disease and health problems in our aquarium.
Fenner, RM. The Conscientious Marine Aquarist. TFH Publications. Neptune City, NJ; 2001.