What is meant by "stressing" fish, and why is stress a badthing?
Most fish can tolerate environmental conditions that differsomewhat from the natural conditions in which they evolved. This doesnot mean, however, that they will be as healthy or live their fullnormal life span. For example, keeping a fish in water that is cooler(or warmer) than its preferred condition forces its body organs towork harder to keep it alive. That is, such conditions place the fishunder increased stress.
Increased stress reduces a fish's ability to ward off diseases andheal itself (e.g., if its fins get nicked, or parasites get introducedinto the tank with newly purchased fish). In addition, stress reducesa fish's ability to breed successfully and shortens its natural lifespan. A small amount of stress by itself is not usually fatal, but asstress levels increase, a fish's ability to cope with it decreases.Thus, one of the most important goals of a fishkeeper is to removesources of stress wherever possible.
It should be noted that eliminating stress does not guarantee thatyour tank will be healthy. But it significantly increases theodds. Many netters boast regularly about how they've kept fish(apparently) "healthy & happy" for long periods of time under(apparently) highly stressful conditions. Such aquarists are sittingon a time-bomb; the not uncommon followup story will refer to one fishgetting sick, then another, with an end result of multiple fishdeaths. Reducing stress simply increases the likelihood that a tankwill stay healthy (much the same way as eating right, exercising,getting the proper amount sleep is generally associated with a longhealthy life for humans).
What are the common factors that lead to stress in aquariums?
In the following, we list some of the more common stress-inducingconditions. In all cases, the level of stress induced by a specificfactor is highly species-dependent. Thus, an aquarist is advised tobe aware of the type of stress that will be present in their tanks andselect fish known to tolerate such conditions well. For example, ifyour water is hard and alkaline, you're best off selecting fish thatthrive under such conditions.Nitrogen compounds (ammonia, nitrite and nitrate) have varying degreesof toxicity and are stressful at all levels. Ammonia is toxic in lowconcentrations. In ANY concentrations, ammonia severely stressesfish. Consequently, a healthy aquarium must have an adequatebiological filter that quickly converts ammonia to nitrite (andnitrate). Although significantly less toxic than ammonia or nitrite,nitrate also stresses fish. Thus, a means of removing excess nitrate(e.g., through regular water changes) helps keep an aquarium healthy.
The water temperature of your tank should match the needs of itsinhabitants. Keeping water temperature too cold or too warm for aparticular species will stress those fish. For example, goldfishprefer cooler temperatures (less than 70F) than most tropical fish(goldfish survive winters in ponds where temperatures approachfreezing), guaranteeing that a tank containing both goldfish andtropicals will either be too cold or too warm for some of theinhabitants.
Some fish prefer soft water, others prefer hard water. Keeping asoft-water preferring fish in harder water (and vice versa) isstressful.
Some fish prefer acidic water, some prefer alkaline water, othersprefer water with a neutral pH. (Some fish don't care too much.)
Some fish live in brackish water conditions; they will do better inwater with a small amount of added salt. Other species are extremelyintolerant of salt. Add salt only if all of a tank's inhabitants cantolerate salinity. Mollies, for example are known to like salt,whereas many species of catfish tolerate no salt at all. In general,fish lacking scales (or having small scales) don't tolerate salt well.
The amount of physical space required for a particular fish depends onits species. Some fish do just fine in a 10g tank, others need 100gor more. Keeping a fish in a tank that is too small for it increasesthe level of stress (on everyone), frequently leading to increasedaggression among tank inhabitants. Note also that the amount of spacerequired may change should fish pair off to breed. Breeding cichlids,for example, claim a portion of the tank for themselves, chasing awayany fish that encroach on its territory. Thus, the onset of breedingbehaviors frequently increases stress levels.
Not all species of fish mix well with others. As an obviousexample, most cichlids will eat smaller tank inhabitants (e.g.,anything they can fit in their mouths). Even if too big to be eaten,however, peaceful fish will be stressed if kept with aggressive fishthat chase them around all day. Moreover, many fish communicatethrough behavior and body language (e.g., cichlids frequentlyestablish a "pecking order" in which one fish is king). Fish of onetype of species may not recognize the signals given off by others,guaranteeing continual strife.
Some fish school in nature, spending their entire lives in largegroups (rather than individually); they never feel comfortable or"safe" when kept by themselves. Cory cats for example, do better in atank with 6 or more other Corys than they do by themselves. While itmay be tempting to buy six different kinds of fish, this may not beideal for the fish themselves. The opposite can also be true. Somefish are more aggressive towards members of their own species (e.g.,mating behaviors), whereas they may not feel threatened by otherspecies and pretty much ignore them.
Fish need oxygen, and some fish are more tolerant of low-oxygen waterthan others. Water with insufficient oxygen stresses fish. Note thatas the water temperature goes up, the amount of dissolved oxygen inwater decreases.
Poor nutrition also causes stress. A healthy diet is a varieddiet, and one should avoid using old foods in which vitamins and othernutrients have broken down. "Old food" includes food that has beenstored in hot places, been exposed to air (not sealed), etc.
The "cure" of adding medicines to tanks is often worse than theoriginal disease. Medications that kill bacteria, parasites, etc. areusually not too discerning: they may also kill your nitrifyingbacteria (now you REALLY have a major problem) or be toxic to the fishthemselves. For example, some species of fish do not tolerate certaintypes of medicines at all. Adding such medications may weaken healthyfish to the point that they become susceptible to the originaldisease.
Adding untreated water to your tank may introduce chlorine orchloramine, both of which are toxic to fish. Be sure to treat allwater prior to adding it to your tank.
Sudden change in water conditions can be stressful. Within limits,most fish can adjust to sub-optimal water conditions (e.g., wrongtemperature, wrong pH). However, fish have difficulty adjusting to aSUDDEN change in water chemistry. Thus suddenly raising (or lowering)the temperature, changing the pH, changing the water hardness,etc. stresses a fish. It is more important to keep the waterchemistry stable over the long haul than keeping water conditionsexactly optimal.
In summary, many factors lead to fish stress. Minimizing andeliminating sources of stress increases the chances of keeping tankinhabitants healthy. The exact amount of a stress individual fish cantake depends greatly on what species it is, its age and size, etc. Astressed fish is a weakened fish. Although it may appear healthy tothe casual observer, it will be more susceptible to disease, injury,etc. In contrast, healthy (unstressed) fish will be able to ward offdisease and infection on their own. Thus, the appearance of diseasein a tank is frequently brought on by "poor water conditions" thatleave fish with weakened immune systems.
How can I tell if my fished are stressed?
In short, stressed fish don't "act normal", with "normal" definedaccording to the species of fish. Once you've had fish for a fewweeks, you'll see that each species behaves in its own characteristicway (that's why fish are fun to have!). Some fish tend to always staynear the top of the water, others near the bottom. Some fish swimcontinuously, others stay in one place. Deviation from that normusually indicates stress.Common symptoms of stress include:
- Fish stays near the surface gasping for breath, indicating that ithas trouble getting enough oxygen (the concentration of dissolvedoxygen is highest near the water's surface). Possible causes includelow oxygen concentration due to poor water circulation, toxins thathave damaged its gills, high ammonia or nitrite levels, etc.
- Fish won't eat, or doesn't eat as aggressively as in past.
- Fish stays hidden continuously and won't come out where it can beseen. Possible causes: aggressive fish, insufficient cover (e.g.,plants, wood, etc.) to make fish feel "safe" while swimming about.
- Fish has nicked fins, open wounds that don't seem to heal. Possiblecause: fish is target of aggression. Normally, minor nicks and cutsheal quickly. If they don't, stress levels may be suppressing thefish's immune system.
- Fish has disease (parasites, fungus, etc.) Of course, the diseaseitself is a major problem. But in most cases, a healthy fish's immunesystem keeps it from getting sick in the first place. Thus, gettingsick is a sign that the fish is in a stressed state (or had been untilrecently).
Next Section: Beginner: Water Chemistry
