Effect of stocking density on survival and growth of critically endangered mahseer, Tor putitora (Hamilton), in nursery ponds

Effects of stocking densities on the growth, survival and production of mahseer (Tor putitora) fingerlings were examined in a single-stage nursery-rearing system. The experiment was conducted for 8 weeks in six earthen nursery ponds having an area of 0.012 h each. Four-day-old hatchlings stocked at 0.6 million/ha was designated as treatment-1 (T1), 0.8 million/ha as treatment-2 (T2) and 1.0 million/ha as treatment-3 (T3). At stocking, all hatchlings were of same age group with a mean length and weight of 1.18 ± 0.04 cm and 0.012 ± 0.003 g, respectively. Hatchlings in all the treatments were fed with Saudi Bangla (SABINCO) commercial fish feed viz., nursery (32.06% crude protein) for the first 14 days and starter-I (31.53% crude protein) from days 15 to 56. Physico-chemical parameters (temperature, secchi disc transparency, dissolved oxygen, pH and total alkalinity) and plankton populations (phyto- and zooplankton) were at the optimum level for fish culture. Highest weight gain was observed in T1 and lowest in T3. Final length, final weight and survival of fingerlings also followed the same trends as weight gain. Fingerlings in T1 produced significantly higher specific growth rate than T3, but not than T2. Feed conversion ratio was significantly higher in T1 followed by T2 and T3 in that order. Significantly higher number of fingerlings was produced in T3 than in T2 and T1, respectively. Despite this, consistently higher net benefits were obtained from T1 than from T3 and T2. Overall, highest growth, survival and benefits of fingerlings were obtained at a density of 0.6 million hatchling/ha. Hence, of the three stocking densities, 0.6 million hatchling/ha appears to be the most suitable stocking density for rearing of mahseer fingerlings in single-stage nursery system.