Plankton is also one of the main sources of food for fish. They are the most common prey for all fish larvae. Plankton has its place in the lower regions of the food chain and is the basic source of food for small aquatic animals like fish larvae. During the early stage of their life cycle fish rely on their yolk sac for nutrition. They also rely on plankton to survive during its development stage. And if the number of plankton decreases, the population of fishes will be greatly affected. This cycle clearly demonstrates the impact of plankton upon pond life. Fish farmers have increased fish yields in ponds by using inorganic or chemical fertilizers and organic fertilizers or "manures." (Bocek, 2009)
When ponds are fertilized with organic and inorganic fertilizers, nutrients stimulate the growth of microscopic plants in the water (phytoplankton). Phytoplankton is food for other organisms (zooplankton and larger animals) that are eaten by fish. Abundant growth of these microscopic plants gives water a turbid, greenish color (called a “bloom”) that can prevent light from reaching the pond bottom and reduce the growth of rooted aquatic weeds. Fish farmers and recreational farm pond owners fertilize ponds to increase fish. Aquaculture ponds are fertilized to increase the available natural food (phytoplankton and zooplankton) for fry or larval fish, or for species that are efficient filter feeders.
Some ponds have very dense algae blooms dominated by one or two species. For reasons that are not well understood, these blooms are subject to spectacular collapse, often called a “crash,” where all the algae suddenly die. This research would highlight the effects of plankton on Tilapia growth using organic and inorganic fertilizers and the causes of phytoplankton blooms to “crashes.”
It was found that when organic fertilizers are used there is a higher phytoplankton bloom and higher oxygen level in the tanks where as when inorganic fertilizers are used there is a greater zooplankton population. When organic and inorganic fertilizers are combined it provides food for fishes and the fishes in the combined tank had the highest weight gained. Brachionus pala and Daphnia pulex which are plankton-feeding animals, will decrease the numbers of the phytoplankton very rapidly when present in high numbers.