Influence of feeding, periphyton and compost application on the performances of striped grey mullet (Mugil cephalus L.) fingerlings in fertilized brackishwater ponds

Abstract

To evaluate the effects of different management systems on performances of grey mullet (Mugil cephalus L.) fingerlings, a 120-day experimental trial was conducted in twelve brackishwater ponds (600 m2 each). Rearing management systems assessed were: fertilization alone (FR), combined fertilization-feeding (FF), fertilizationperiphyton (FP) and fertilization-compost application (FC) in triplicate ponds. Soaked mustard cake was used as a fertilizer @ 100 kg ha−1 at 15-day intervals in all the treatment ponds. Formulated crumble diet containing 29.7% protein and 4.9% lipid was used as a supplementary feed in FF. Bamboo poles were used as substrates (equivalent to 10% of pond surface area) to facilitate periphyton growth in FP and composted aquatic weed was applied @ 500 kg ha−1 in FC at monthly intervals. Ponds were stocked with grey mullet fry (3.36 ± 0.32 g/ 63.70 ± 4.61 mm) at 30,000 number ha−1. The experiment revealed significant differences in most of the water quality parameters among the four treatments. In FP ponds, a significant reduction (P < 0.05) in inorganic nitrogen and phosphorous, chlorophyll-a contents, and plankton population was observed. The highest fish growth (28.39 ± 1.94 g) and survival (94.3 ± 4.2%) were recorded in FP followed by in FF, FC and FR (P < 0.05). A significantly higher total fish biomass (P < 0.05) was obtained in FP (803 ± 29 kg ha−1) followed by in FF (730 ± 37), FC (507 ± 33) and FR (362 ± 22). Condition factor (K) and isometric exponent (b) of length-weight relationship indicated that fingerlings were in better condition with isometric growth (K=1.37 ± 0.13; b =3.01 ± 0.12) in FP. Inferior condition with allometric growth was observed in FR, FF and FC systems. These results suggest that periphyton based system can be an appropriate rearing technique for grey mullet fingerling production in brackishwater fertilized ponds as an environment-friendly and sustainable practice.