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 (T 1), 0.8 million/ha as treatment-2 (T 2) and 1.0 million/ha as treatment-3 (T 3). 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 T 1 and lowest in T 3. Final length, final weight and survival of fingerlings also followed the same trends as weight gain. Fingerlings in T 1 produced significantly higher specific growth rate than T 3, but not than T 2. Feed conversion ratio was significantly higher in T 1 followed by T 2 and T 3 in that order. Significantly higher number of fingerlings was produced in T 3 than in T 2 and T 1, respectively. Despite this, consistently higher net benefits were obtained from T 1 than from T 3 and T 2. 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.