Integration of pen aquaculture into ecosystem-based enhancement of small-scale fisheries in a macrophyte dominated floodplain wetland of India.

The rapid degradation, overexploitation, and encroachment of floodplain wetlands have led to considerable decline in fish diversity and production from these invaluable aquatic resources threatening livelihood of the dependent fishers. The climate change evident in the fast few decades has further aggravated the problem of eutrophication causing water stress and sedimentation leading to rampant macrophyte proliferation affecting ecological and economic functioning of these ecosystems. Macrophyte control and management needs serious attention for sustaining ecosystem services provided by these resources. In this direction, pen culture of grass carp Ctenopharyngodon idella as a biocontrol for macrophytes along with Indian major carps was implemented in a co-management mode in Beledanga, a typical floodplain wetland, a gradually shrinking, macrophyte dominated floodplain wetland in lower Ganga basin. Indian major carps Labeo catla (6.28±0.23g), Labeo rohita (5.1±0.12g), Cirrhinus mrigala (3.5±0.08g) were stocked in the ratio 4:3:3 at the rate of 20 Nos.m in pens (0.1ha each) in triplicate. Grass carp (7.1±0.42g) was stocked in pen at the rate of 20Nos.m in duplicate. The fishes were fed with pelleted feed twice a day at the rate of 2-3% of body weight. The seed was overwintered in pens for a period of 90 days from November 2019 to January 2020. Average weight recorded at the end of culture period was 25.13±1.70g, 18.11±0.63g, 14.53±0.87g, and 39.20±1.90g in L. catla, L. rohita, C. mrigala, and C. idella, respectively. The survival of fish ranged from 70 to 81%. Growth performance and feed utilization efficiency of grass carp were significantly higher (p<0.05) compared to other carp species. The pen culture was found to be economically viable with a benefit cost ratio of 1.53. The fishes produced were released back into the open wetland as an additional input for culture-based fisheries. The intervention along with niche-based enhanced stocking led to 24% increase in the fish production from the wetland with grass carp contributing 20-22% of the total catch with 32% increase in revenue generated by the sale of fish within a short span of 1 year. The study successfully demonstrated technological suitability and economic feasibility of pen culture in this wetland and role of grass carp as a potential biocontrol species for macrophyte management. Grass carp stocked in open wetland grew to 0.8 to 1kg within 6 months and 2-2.3kg within a year and could utilize 40-45% of the submerged and emergent macrophytes. Integration and optimization of grass carp will not only aid in habitat management of macrophyte-choked wetlands but will also boost their small-scale fisheries by converting standing macrophyte biomass into protein-rich fish biomass. The enhanced production will also cater to nutritional and livelihood security of the dependent fishers.