By Donna M. Recktenwalt
It’s called fright syndrome, and we’ve all seen it: for no apparent reason, a fish suddenly begins a mad dash around the tank, bumping into walls and knocking into other objects before subsiding, motionless or quivering, on the bottom of the tank. Not only is this stressful to individual fish, the fright can be communicated to other fish in the tank, and in severe cases can sometimes lead to death.
What triggers this response? What can we do to prevent it? If it does happen, what can we do to treat it?
Fright syndrome can be triggered by suddenly turning on bright lights, by sudden movements near the tank (apparent predation) and by environmental stresses such as extremely low pH levels, extremely poor water conditions, or an apparent lack of security for the fish in the form of hiding places or plants.
A few steps by the aquarist to make fish comfortable and happy can help.
Add plants to your tanks. Plants provide security in the form of cover and also help to improve overall water quality. Java moss is perhaps the most widely used and most effective plant for killie tanks, growing well in low light levels, removing CO2 and ammonia, and providing an ideal spawning medium.
Arrange your lighting system for a gradual start, with a dim light coming on first before the full bright lighting array. This will help prevent the startle response.
Do regular partial water changes. Some aquarists have noticed that when pH levels drop below 4.9, the incidence of fright syndrome (and subsequent fish deaths) increase.
– G.C.K.A. Newsletter, April 1999