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

Abstract

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.