Effect of varying closes of organic and inorganic fertilizers on plankton production and fish biomass in brackish water fish ponds

Abstract

The effects of four different doses of organic (cowdung) and inorganic fertilizers (single super phosphate: SSP) in combination were studied on plankton production, species diversity and fish biomass in saline and freshwater fish ponds. Physico-chemical factors of pond waters were also monitored. Alkalinity and nutrients increased with increase in the dose of fertilizers. Dissolved oxygen (DO) also remained sufficiently high up to the third treatment; however, levels declined significantly in the ponds receiving the fourth treatment (20 000 kg ha-1 year-1 of cowdung and 3000 kg ha-1 year-1 of SSP). The highest plankton population, species diversity and higher fish biomass was also observed in ponds which received the third dose of fertilizers (10 000 kg ha-1 year-1 of cowdung and 1500 kg ha-1 year-1 of SSP). However, a decline in these parameters was observed in ponds which received the highest (fourth treatment) dose of fertilizers. Nutrients remained slightly lower in brackish-water fish ponds. When species diversity values were compared, it was observed that, although values werte higher in freshwater ponds, their abundance (no. 11) remained lower than in brackish-water fish ponds. Similarly, fish biomass also remained significantly higher in brackish-water ponds than in freshwater ponds. From these studies, it can be concluded that a combination of 10 000 kg of cowdung + 1500 kg ha-1 year-1 of SSP appears to be the optimum dose.