Environment

Temperature of the water :

The temperature of the water in which fish live is very important. In the first place it has very considerable influence on its oxygen content, because the solubility of any gas decreases as the temperature rises. Water that is satisfactory for a particular species when it is colder might prove lethal when it because too hot because the oxygen has been driven off.

The optimum temperature of the water varies for different fish, so they will not naturally live together in the same environment. as an example, that for brown trout is between 45 F (12 c) and 60F (15c) whereas that for carp is between 72F (22c) and 77F (25c) . These figures are consistent with the fact that brown trout revel in the cold, well oxygenated  waters of, mountain streams, while carp are happy in warm oxygen is much lass abundant.

Rainbow trout tolerate higher temperatures and lower oxygen concentration than brown trout. Consequently it is possible to come to a compromise and have some ponds in which rainbow trout and carp will live reasonably will together and flourish.

Fresh clean water :

The water in a pool containing fresh-water fish must be fresh. No account must it become brackish (there is a rare possibility of this happening if the pool is replenished form an old well ). It must not be allowed to because stagnant, because it might contain substance. Obnoxious to fish. There must be no decaying organic matter present as these produce toxic gases harmful to fish.