Influence of inorganic fertilizer application and supplementary feeds on periphyton biomass, quality and species composition

Journal Article Volume 5; Issue 4; 2020; Page No. 70-78

A study was conducted to assess the effects of fertilization alone (T 1 ), supplementary feeding alone (T 2 ) and combination of fertilization plus supplementary feeding (T 3 ) on periphyton species composition, quantity and quality. Sex-reversed Oreochromis niloticus fingerlings were stocked in earthen ponds one week after initial pond fertilization. Urea and Diammonium phosphate (DAP) fertilizers were applied in pond water at weekly intervals at a rate of 3 and 2 g/m 2 , respectively. Fish were fed feed containing 25.1% crude protein at 5% (T 2 ) and 2.5% (T 3 ) of fish body weight daily. The results show that the ponds under combination of fertilization plus supplementary feeding (T 3 ) had higher periphyton biomass (47.35 ± 7.64 g DM/m 2 ), crude protein content (11.40 ± 0.16%) and organic matter content (OM) (25.47 ± 0.28%). The periphyton from ponds under fertilization alone (T 1 ), had the highest ether extract content (1.84 ± 0.07%) and ponds treated with supplementary feeding alone (T 2 ) had higher phosphorous content (0.48 ± 0.0 mg/L). The body of fish cultured in ponds under T 3 had higher CP (69.14 ± 0.33%) and OM (96.65 ± 0.16%) contents while those reared under T 1 had higher ether extract content (18.33 ± 0.19%) and ash content (4.78 ± 0.1%), suggesting a positive relationship between algal quality and fish muscles. In addition, fish growth rate increased as the periphyton quantity (biomass and OM) and quality (CP and phosphorous) increased. The study also revealed five classes of phytoplankton (Bacillariophyceae, Chlorophyceae, Cyanophyceae, Euglenophyceae and Zygnematophyceae) and three classes of zooplankton (Eurotatoria, Heterotrichea and Oligohymenophorea). In general, both phytoplankton (algae) and zooplankton were more abundant in ponds under T 3 than in ponds under the other treatments. It is concluded that the combination of fertilization plus supplementary feeding (T 3 ) produces higher periphyton quantity, quality and species composition and thus promotes higher fish growth rate compared to feeding alone and fertilization alone treatments.