FOOD CHAINS

In nature

Life in water, as on land, is not possible without light. Vegetation (microscopic plankton or plants) absorbs it with carbon dioxide (CO2) and uses the mineral salts, which act as nutrients. This vegetation serves as food for herbivorous or omnivorous fish, which in their turn provide nutrition for carnivorous fish. From this point, the next link in the chain can be aquatic (dolphin, shark), terrestrial (man), or aerial (bird). When aquatic organisms die, they fall to the bed. Their bodies are degraded by the action of bacteria, the material is recycled into mineral salts, and so the chain comes full circle. (While they are alive, it is their excreta that are recycled.)

In a aquarium

In a aquarium, the chain is simple: it is obviously out of the question to have carnivorous fish cohabit with their prey! The fish are fed by the aquarist, although in some cases they can feed on the vegetable matter growing in the aquarium.