Question: My fish instead of swimming stick to the surface of water and produce smacking sounds. What is going on?"
Answer: The fish behave this way, because there's not enough oxygen dissolved in the water and they have to gulp the atmospheric air with their mouths. In scientific terms this phenomenon is called anoxia, or oxygen starvation.
When fish live long in the lack of oxygen, they have a poor appetite, grow slowly, their reproductive organs undergo changes so that they can't give posterity. If such fish are still able to lay eggs, the spawn often perishes or the hatched fries die later. It may happen that the fries survive. In this case they grow very slowly, despite nourishing food.
Exposed to lack of oxygen the fish finally can die from choking (asphyxia). If the fish begin to choke, you should change part of water in the tank and place an air pump - the device that sucks the air and blows out a flow of very small bubbles that enrich the water with oxygen.
If case of a hard oxygen deficiency add a 15% solution of hydrogen peroxide (1 drop of concentrated hydrogen peroxide per 2 l of water).
In order to prevent oxygen deficiency, add some aquatic plants and attach an electric lightning above the water surface since plants produce oxygen in the presence of light. The "day" in winter should last 10 to 12 hrs, in summer - 15 hrs.
If the problem of anoxia exists in the presence of live plants in the aquarium, suppose if there are not too many. In the absence of light plants can't produce oxygen, just the opposite: every night they breathe and thus consume a great deal of oxygen.
Never overfeed fish. The remained food and dead parts of plants should be removed daily: the decay of organic substance entails oxygen consumption.
The more inhabitants live in the aquarium, the more oxygen is needed. Therefore move the extra fish and other inhabitants (especially mollusks) to some other tank. How to know, who and how many are the extra? This is a difficult question, since much depends on volume and shape of the tank, air pump ability, as well as on the fish type, size and biological characteristics. Approximate number of fish in the tank should be counted as follows. In 40-50 l tank with no aeration every 2 in. of fish body length needs 2 l of water. Thus at length 3-5 in. the fish needs 3-4 l. A fish longer than 5 in. requires 8-10 l of water.
By Lyudmila Stushkovskaya. 1000 advices about how to treat pets
Translated by Tatiana Karpova (Moscow)
(MSU, Biology faculture, Dep. zoology and ecology).