Effects of stocking density, feeding, fertilization and combined fertilization-feeding on the performances of striped grey mullet (Mugil cephalus L.) fingerlings in brackishwater pond rearing systems

Growth, survival, biomass production and body composition of striped grey mullet (Mugil cephalus L.) fingerlings were evaluated in two pond experimental trials as a function of two stocking densities and three management systems in brackishwater pond rearing. The three management systems tested were feeding, fertilization and combined fertilization-feeding. The Experiment 1 had a 2 × 2 factorial design with two levels of stocking density and two types of pond management system (feeding and fertilization) resulting in four treatments in triplicates: stocking density 1 + feeding (S1F1), stocking density 1 + fertilization (S1F2), stocking density 2 + feeding (S2F1) and stocking density 2 + fertilization (S2F2). Twelve ponds (600 m2 each) were stocked with grey mullet fry (0.17 ± 0.02 g/23.8 ± 0.6 mm) at 7500 number ha− 1 in treatments S1F1, and S1F2 and at 15,000 number ha− 1 in treatments S2F1, and S2F2. In Experiment 2, three different pond management systems evaluated as three treatments (in triplicate ponds) were FR: fingerling rearing with fertilization; FD: fingerling rearing with feeding and FF: fingerling rearing with combination of fertilization + feeding. Nine ponds (600 m2 each) under the three treatments were stocked with grey mullet fry (0.55 ± 0.08 g/36.0 ± 2.1 mm) at 15,000 number ha− 1. In S1F1, S2F1, FD and FF, formulated feed containing 27.5% crude protein was provided at 3.5-20% body weight daily, whereas, in S1F2, S2F2, FR and FF systems, ponds were fertilized fortnightly with cattle manure, urea and single super phosphate at 500, 30 and 30 kg ha− 1, respectively. In Experiment 1, although stocking density and application of feed or fertilization did not affect the growth parameters, survival and apparent feed conversion ratio (P > 0.05) of grey mullet, coefficient of variation at harvest weight (CVhw) and total harvested biomass were influenced by feeding or fertilization (P < 0.05). In Experiment 2, significantly better growth, lower CVhw and higher total harvested fish biomass were obtained in fishes of FF compared with that of FR and FD (P < 0.05). From the pond trials it can be concluded that combined fertilization-feeding system with a stocking density of 15,000 fry ha− 1 would be appropriate for production of striped grey mullet fingerlings in brackishwater ponds. The present findings indicate feasibility of establishing M. cephalus seed rearing practice using a cost-effective and resource-efficient approach.