49 Common Causes of Stress in the Aquarium
Description
This article is from the Beginning Fishkeeping FAQ, by Thomas Narten with numerous contributions by others.
49 Common Causes of Stress in the Aquarium
In this section, we list some of the more common stress-inducing
conditions. In all cases, the level of stress induced by a specific
factor is highly species-dependent. You should be aware of the type of
stress that will be present in your tanks and select fish known to
tolerate such conditions well. For example, if your water is hard and
alkaline, you're best off selecting fish that thrive under such
conditions.
Nitrogen compounds (ammonia, nitrite and nitrate) have varying degrees
of toxicity and are stressful at all levels. Ammonia is toxic in low
concentrations and severely stresses fish under ANY concentration.
Consequently, a healthy aquarium must have an adequate biological
filter that quickly converts ammonia to nitrite (and nitrate).
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 its
inhabitants. Keeping water temperature too cold or too warm for a
particular species will stress those fish. For example, goldfish
prefer cooler temperatures (under 70F) than most tropical fish
(goldfish survive winters in ponds where temperatures approach
freezing), guaranteeing that a tank containing both goldfish and
tropicals will either be too cold or too warm for some of the
inhabitants.
Some fish prefer soft water, others prefer hard water. Keeping a
soft-water preferring fish in harder water (and vice versa) is
stressful.
Some fish prefer acidic water, some prefer alkaline water, others
prefer water with a neutral pH. (Some fish don't care too much.)
Some fish live in brackish water conditions; they will do better in
water with a small amount of added salt. Other species are extremely
intolerant of salt. Add salt only if all of a tank's inhabitants can
tolerate 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 on
its species. Some fish do just fine in a 10g tank, others need 100g or
more. Keeping a fish in a tank that is too small for it increases the
level of stress (on everyone), frequently leading to increased
aggression among tank inhabitants. Note also that the amount of space
required may change should fish pair off to breed. Cichlids, for
example, claim a portion of the tank for themselves when in breeding
form, chasing away any fish that encroach on their territory. Thus,
the onset of breeding behaviors frequently increases stress levels.
Not all species of fish mix well with others. As an obvious example,
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 fish that chase
them around all day. Moreover, many fish communicate through behavior
and body language (i.e., cichlids frequently establish a ``pecking
order'' in which one fish is king). Fish of one type of species may
not recognize the signals given off by others, guaranteeing continual
strife.
Some fish school in nature, spending their entire lives in large
groups (rather than individually); they never feel comfortable or
``safe'' when kept by themselves. Cory cats for example, do better in
a tank with 6 or more other Corys than they do by themselves. While it
may be tempting to buy six different kinds of fish, this may not be
ideal for the fish themselves. The opposite can also be true. Some
fish are more aggressive towards members of their own species (e.g.,
mating behaviors), whereas they may not feel threatened by other
species and pretty much ignore them.
Fish need oxygen, and some fish are more tolerant of low-oxygen water
than others. Water with insufficient oxygen stresses fish. Note that
as the water temperature goes up, the amount of dissolved oxygen in
water decreases.
Poor nutrition also causes stress. A healthy diet is a varied diet,
and one should avoid using old foods in which vitamins and other
nutrients have broken down. ``Old food'' includes food that has been
stored in hot places, been exposed to air (not sealed), etc.
The ``cure'' of adding medicines to tanks is often worse than the
original disease. Medications that kill bacteria, parasites, etc. are
usually not too discerning: they may also kill your nitrifying
bacteria (now you REALLY have a major problem) or be toxic to the fish
themselves. For example, some species of fish do not tolerate certain
types of medicines at all. Adding such medications may weaken healthy
fish to the point that they become susceptible to the original
disease.
Adding untreated water to your tank may introduce chlorine or
chloramine, both of which are toxic to fish. Be sure to treat all
water prior to adding it to your tank.
Sudden changes in water conditions can be stressful. Within limits,
most fish can adjust to sub-optimal water conditions (e.g., wrong
temperature, wrong pH). However, fish have difficulty adjusting to a
SUDDEN 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 water chemistry
stable over the long haul than to keep keep water conditions exactly
optimal.
In summary, many factors lead to fish stress. Minimizing and
eliminating sources of stress increases the chances of keeping tank
inhabitants healthy. The exact amount of stress an individual fish can
take depends greatly on what species it is, its age and size, etc. A
stressed fish is a weakened fish. Although it may appear healthy to
the casual observer, it will be more susceptible to disease, injury,
etc. In contrast, healthy (unstressed) fish will be able to ward off
disease and infection on their own. Thus, the appearance of disease in
a tank is frequently brought on by ``poor water conditions'' that
leave fish with weakened immune systems.
Continue to:
My Books
