Effects of three fertilizer treatments on zooplankton productivity in plastic tanks

Abstract

Zooplankton productivity resulting from 3 fertilizer treatments (organic, inorganic and combination of organic and inorganic) was evaluated in 12 outdoor circular plastic tanks during a 21-day experiment; fertilizers were applied on weekly basis. The density of zooplankton varied significantly (P<0.05) with the type of fertilizer applied; organic fertilizer was the most productive while inorganic and the combination of organic and inorganic ranked second and were both equally productive (P>0.05). A combination of organic and inorganic fertilizer can, therefore, substitute for complete inorganic fertilization in certain situations. There was also a significant difference (P<0.05) in the qualitative composition of zooplankton produced by the fertilizers. Organic fertilizer produced more of the smaller-sized zooplankters (rotifers, cladocerans) and should be preferred in primary nursery ponds while inorganic fertilizer favoured the production of larger-sized zooplankters (copepods) and should be more relevant in the preparation of secondary and tertiary nursery ponds; fertilizers should be applied at least 1 week prior to stocking of hatchlings to ensure that the zooplankton forage base is well established.