Studies on the growth, survival and production of endangered mahseer, Tor putitora (Hamilton, 1822) at different stocking densities in primary nursing

Abstract

The research work was conducted in six nursery ponds of 0.01 ha each with 4 days old mahseer, Tor putitora spawn at three different stocking densities viz., 1.50, 1.75 and 2.00 million spawn/ha each having two replicates. Fries were fed same diet of MEGA fish feeds in three different treatments containing 40.57% crude protein (pre-nursery feed) for the first 14 days and 35.52% crude protein (nursery feed) for the second 14 days. The feeding rate was 20 kg/ million spawn/ day for the first 2 weeks and 24 kg/ million spawn/ day for the second 2 weeks. The physico-chemical characteristics of pond water were measured weekly. The mean values of some water quality parameters such as temperature (°C) were 22.50±0.35 (T1), 22.69±0.39 (T2), 22.81±0.37 (T3); transparency (cm) 28.38±2.00 (T1), 41.88±2.45 (T2), 52.25±1.93 (T3); dissolved oxygen (mg/l) 4.90±0.21 (T1), 4.42±0.15 (T2), 3.72±0.07 (T3); pH 7.34±0.22 (T1), 7.21±0.23 (T27.53±0.21 (T3) and alkalinity (mg/l) 92.38±3.06 (T1), 112.13±6.48 (T2), 117.38±5.75 (T3) from 28 days, respectively. The ranges of water quality parameters were suitable for fry and fingerling rearing. The highest weight gain was recorded in T1 (1.79±0.03) and the lowest in T3 (1.46±0.04). The mean value of final weight (g) was 1.81±0.02, 1.71±0.02 and 1.52±0.03 in T1, T2 and T3, respectively. Significantly lower specific growth rate was found in T3 (7.23±0.04) than T1 (7.54±0.02) and T2 (7.45±0.02). Fingerlings in T3 produced significantly higher food conversion ratio (0.61±0.10) than T1 (0.44±0.07) and T2 (0.48±0.04). The survival rate of mahseer was 63.05±0.59% (T1), 60.38±0.51% (T2) and 55.19±0.70% (T3), respectively. Significantly higher number of fingerlings was produced in T3 (1103700±10608) than T1 (945675±9320) and T2 (1056650±10314), respectively. But the simple cost benefit analysis showed that higher net benefits were obtained in T2 (TK. 13, 09,968) where the ponds stocked with 1.75 million spawn/ha. Hence, it seems that, among the three tested stocking densities, 1.75 million spawn/ha is the most efficient stocking density for primary nursing of mahseer spawn.