Ecosystem-based fishery enhancement through pen culture of Indian major carp Labeo catla in a tropical floodplain wetland of North Eastern Region, India, during COVID pandemic

The present study was conducted with the objective of developing ecologically and economically feasible pen culture protocols for Labeo catla as an alternate income source for wetland fishers in the context of the COVID-19 pandemic. Yearlings of L. catla (12.33 ± 1.99 cm mean total length and 26.05 ± 6.57 g mean weight) were reared in HDPE pens (500 m² area each) at three different stocking densities of 3 (SD3), 6 (SD6) and 9 (SD9) no. m^-2 in triplicates. Fishes were fed with floating pelleted feed containing 28% crude protein and 5% crude lipid two times daily at 1.5-3% of body weight. During the culture period, fish grew from 26.05 ± 6.57 to 434.61 ± 30.63 g, 306.13 ± 10.68 g and 221.13 ± 14.92 g, respectively, at stocking densities of 3, 6 and 9 no. m^-2 respectively. Weight gain percentage and specific growth rate declined with increase in stocking density. Gross fish yield increased with increase in stocking density and was highest at SD9 (657.92 ± 53.55 kg pen^-1), while net fish yield increased initially from SD3 to SD6 (594.31 ± 29.72 kg pen^-1) and then declined with further increase in stocking density. Important water quality parameters influencing fish growth were measured, and significant difference (p > 0.05) was not observed between treatments (inside pens) and reference site (outside pen at 10-m distance). Weight gain was positively correlated (p < 0.05) to water temperature (r = 0.989) and total phosphorus (r = 0.81). Benefit cost ratio and net return was highest at SD3 (1.61; US $518.88, respectively). Stocking density of 3 no. m^-2 can be considered economically feasible for table fish production of L. catla in pens. Post pen culture, monthly income of fishers increased by 10.76-179.11%, with a mean increase of 90.57%, compared to the period of first COVID-19 wave in India. The present findings can provide an impetus for effective utilization of pen enclosures for income generation and livelihood enhancement of small-scale wetland fishers during pandemic.