The reason why fish always open mouth, because it needs to breathe. Unlike organisms that breathe with lungs, fish have gills as their respiratory organs, and the purpose of opening their mouths is to let water flow through the mouth and then out of the gills, while the gills have gill filaments, which have a large number of blood vessels, and when filtering water, gas exchange will take place, thus obtaining oxygen. In addition, some fish can breathe with auxiliary organs, such as skin, intestine, gill and so on.
1. The dissolved oxygen is too low: Usually, the fish growing in nature will not encounter the situation that the dissolved oxygen is too low. However, artificial breeding is possible. This is because the area of the breeding pond itself is not large, and the density of the fish is relatively high. Therefore, the demand for oxygen is very high. If the oxygen is not filled in time, the fish will suffocate to death.
2. Diving too deep: Although a fish in the wild will not suffocate to death due to insufficient oxygen in the water, diving too deep will also cause it to drown. This is because the fish adjusts its specific gravity through the swim bladder, which facilitates its floating or diving in the water, but as it swims deeper and deeper, the strong pressure will cause it to be unable to adjust the swim bladder, so it can only swim deeper, and eventually it can not breathe and die.
3. Gill disease: If the gills of fish are infected with bacterial diseases or parasitized by parasites, it will also affect their breathing. If not treated in time, the fish will slowly be suffocated to death.
