Introduction: Chlorophyll a concentration proxies the phytoplankton biomass which directly involves in signifying the production functions of aquatic ecosystem. Thus, it is imperative to understand their spatio-temporal kinetics in lotic environment with reference to regional climatic variabilities in the tropical inland waters. Objective: In-situ studies were conducted to examine the changes in phytoplankton biomass in lower Ganga basin as influenced by various environmental parameters under regional climatic variability during 2014-2016. Methods: Firstly, the most key influential environmental parameters on riverine Chl-a concentration were determined. Then the direct cascading effect of changing climatic variables on key environmental parameters were derived through modeling and quantified probable changes in mean Chl-a concentration in the lower stretch of river. Results: Only five environmental parameters namely water temperature, total dissolved solid, salinity, total alkalinity and pH were key factors influencing Chl-a (Multiple R2: 0.638, P < 0.05). Present estimates indicate that if the present rate of regional climatic variability over the last 3 decades (mean air temperature + 0.24 °C, total annual rainfall -196.3 mm) remain consistent over the next three decades (2015-2045), an increase in mean Chl-a by + 170 µgL-1 may likely be expected grossly reaching about 475.94 µg L-1 by the year 2045 or more. Conclusions: The present study is first such comprehending a gross hint towards the probable ecosystem response with an alternative model based methodology in data-deficient situations. Subsequently, the output would also be of great benefit for increase water governance and developing strategy protocol for sustainable water management for greater ecosystem services.

Labeo bata fry were reared in high-density polyethylene (HDPE) pens at different stocking densities to determine growth, survival, feed utilization efficiency and economics in Borkona beel, Barpeta, Assam. Pens (500 m² each) were stocked with fry at four stocking densities, 3 (SD3), 5 (SD5), 7 (SD7) and 9 (SD9) no. m⁻² in triplicates. Feeding was performed twice a day at a rate of 3–5% body weight with floating pelleted feed containing 28% crude protein. Fish grew from 2.38 ± 0.30 g to 82.78 ± 3.18, 75.94 ± 0.89, 71.94 ± 0.89 and 61.81 ± 3.35 g at stocking densities of 3, 5, 7 and 9 no. m⁻², respectively. Weight gain per cent ranged from 2491.85 ± 140.56 to 3371.33 ± 133.16 and specific growth rate from 1.41 ± 0.02 to 1.55 ± 0.02, both of which decreased with increasing stocking density. The net and gross yields increased with increasing stocking density and were highest at SD9. The benefit-cost ratio was maximum at SD7 (1.42), followed by SD9 (1.41). Post-pen culture, the monthly income of fishers increased by 6.10% (SD3) to 40.50% (SD9). Significant differences (p > 0.05) in water quality parameters were not observed between treatments (inside pens) and reference site (outside pen at 10 m distance). Weight gain exhibited a significant positive correlation with temperature (r = 0.92; p = 0.029) and alkalinity (r = 0.95; p = 0.014). The present study can provide impetus towards species diversification in pen enclosures, income enhancement of small-scale wetland fishers and sustainable ecosystem-based floodplain wetland fisheries management.

Length–weight relationships were determined for two small indigenous cyprinid fishes: Osteobrama cotio (Hamilton, 1822) and Salmophasia phulo (Hamilton, 1822) collected from Panchet reservoir, Damodar River, India. About 143 specimens of Osteobrama cotio (5.2–10.4 cm TL) and 113 specimens of Salmophasia phulo (2.9–8.2 cm TL) were collected from November 2014 to June 2016 using gillnets of mesh size ranging from 25 to 120 mm (STR) and dragnets of mesh size 10–20 mm (STR). No previous information on LWRs for these two species from an Indian reservoir was available in the literature.

Wetlands are among the most productive of all aquatic ecosystems. In developing countries, millions of marginal fishers rely solely on wetlands for security of both nutrition and livelihood. The decline in wetland fisheries owing to anthropogenic and climatic changes has made fishers increasingly vulnerable. Pen culture can be an effective climate-resilient technology for enhancing fish production in shallow, macrophyte-choked, and multi-stake floodplain wetlands, especially in eastern and north-eastern India. In this context, pen culture was implemented as an adaptive measure in a tropical Gangetic wetland (Mathura) to enhance fish production and increase the adaptive capacity of fishers. Indian Major Carps, Gibelion catla, Labeo rohita, and Cirrhinus mrigala of initial size 10.4±.21g, 8.2±0.48g, and 6.5±0.23g respectively, were stocked at the ratio of 4:4:2 and at the rate of 30 fish m-2 each in pens of 100 m2 in duplicate. For purposes of conservation, Labeo bata and Gudusia chapra, 4.3±0.18g and 3.8±.34g initial size, respectively, were stocked at the rate of 20 Nos.m-2 each at the ratio of 1:1. The fish were fed with commercial feed at the rate of 4% of body weight. A net survival of 82%, 87%, and 75% was recorded in Indian Major Carps, L. bata and G. chapra. A production of 380 kg IMC was achieved during 120 days of the culture period. L. bata achieved an average weight of 21.40±0.34g during the 90-day culture period, with a survival rate of 87%. G. chapra attained an average weight of 16.5±0.42g during the culture period, with a recorded survival rate of 75%. G. chapra was observed to spawn in the pen. The water quality inside pens and reference sites did not differ significantly (p>0.05). The produced fish were released in the wetland for fisheries enhancement. The present communication discusses the technological suitability and economic feasibility of adopting climate-resilient pen culture as an adaptation measure for enhancing the adaptive capacity of wetland fishers in the face of a changing climate.

Small indigenous fish (SIF) production from wetlands provides nutritious food and supports the livelihood of the fishing community. The present study investigated the fish production trend, SIF diversity, and role of environmental and climatic parameters in Beledanga, a floodplain wetland in lower Ganges, through the sampling and collection of data from the local fishermen cooperative society. The fish catch composition in the wetland shifted after 2019, with the increased Ctenopharyngodon idella (grass carp) contribution from 11% to 17% due to the introduction of in situ seed-raising technology of an HDPE (high-density polyethylene) pen culture system. The fish fingerling stocking has a profound impact on fish production (R² = 0.60, p = 0.007). During the study period, 19 species of SIF were recorded, with a higher abundance observed in the monsoon season. The naturally occurring SIF contributed 16% of the total fish catch, with the highest catch in 2011 (11,970 kg). Water pH and phosphate content are the two most important environmental parameters that influence SIF. The generalized additive model (GAM) indicated that the optimum annual rainfall for fish production in the wetland was between 750 and 1250 mm. The average annual fish production of 43,017 kg through stocking and SIF support the livelihood and nutritional security of the fishers. As the SIF showed a decreasing trend of production, habitat protection, scientific stocking, and in situ enclosure culture are recommended for sustainable enhancement of fish production and to conserve the SIF diversity.