saurav Nandy

Temperature and seasonal rainfall along with other environmental variables are important in regulating the reproductive cycles in teleost fishes. Certain environmental variables may act as cues for reproduction and changes in these may affect seasonality and success of reproduction, as fishes are known to integrate their physiological functions with environmental cycles. Wetlands are sensitive to climate change due to their shallow and confined nature. Since wetlands are important spawning and nursery grounds for many fishes, changes in the environmental variables may have direct consequences for the spawning and survival of fish. In the present study, we have assessed climatic and water chemistry variables capable of influencing seasonality in environmental variables as well as gonadal maturation of spotted snakehead Channa punctata, to predict threshold values of Gonado Somatic Index in females and a favourable range of identified climatic and water chemistry variables for breeding success. Among the climatic and water chemistry variables studied, seasonal variation in rainfall was found to have the most profound effect on gonadal maturation and breeding in C. punctata, followed by water temperature. The favourable range of rainfall obtained varied between 800 mm to 1400 mm, corresponding to the water temperature range between 29 °C and 31 °C. An overall significant warming trend with a reduction in total rainfall has been observed with changes in seasonal trends in temperature and rainfall in the study area. The rainfall being the major climatic factors influencing water chemistry in the wetlands during the spawning season, changes in rainfall pattern may influence breeding periodicity of C. punctata in wetlands in climate change scenario.

Wetlands are biologically sensitive habitats and envisaged as the most impacted systems by climate change. Floodplain wetlands of West Bengal, India, are important fisheries resources and provide tremendous economic and ecological services. There is lack of long-term quantified data to assess the impacts of climate change on floodplain wetlands fisheries in India. The article presents a stakeholder-driven approach to quantify the impacts of climate change on wetland fisheries. A modified Delphi method has been used to accomplish this. The present article discusses the modified methodology and the results obtained thereof. The study identified around seven potential climate change-induced threats on wetland fisheries among which water stress (95% consensus), wetland accretion/sedimentation (85%), aquatic weed proliferation (70%) and loss of wetland connectivity (65%) are high-priority issues demanding immediate management action. These issues are expected to further aggravate in future climatic scenario.

The concept of threshold condition factor (Fulton), beyond which more than 50% of the female fish population may attain readiness for spawning coined as pre-spawning fitness (Kspawn50), has been proposed in the present article and has been estimated by applying the non-parametric Kaplan-Meier method for fitting survival function. A binary coding strategy of gonadal maturity stages was used to classify whether a female fish is “ready to spawn” or not. The proposed Kspawn50 has been generated for female Mystus tengara (1.13–1.21 units), M. cavasius (0.846–0.945 units), and Eutropiichthys vacha (0.716–0.799 units). Information on the range of egg parameters (fecundity, egg weight, egg diameter) expected at the pre-spawning stage was also generated. Additional information on species-specific thermal and precipitation window (climate preferendum) within which Kspawn50 is attained was also generated through the LOESS smoothing technique. Water temperatures between 31 and 36 °C (M. tengara), 30 and 32 °C (M. cavasius), and 29.5 and 31 °C (E. vacha) and monthly rainfall between 200 and 325 mm (M. tengara), > 250 mm (M. cavasius), and around 50 mm and between 350 and 850 mm (E. vacha) were found to be optimum for attainment of Kspawn50. The importance of parameterization and benchmarking of Kspawn50 in addition to other conventional reproductive biology parameters has been discussed in the present article. The purposes of the present study were fulfilled by generating baseline information and similar information may be generated for other species replicating the innovative methodology used in this study.

Reproductive biology of female amphidromous croaker Johnius coitor (Hamilton, 1822) was studied for the first time from various freshwater stretches of Ganga river basin, India in relation to climatic variability. The species showed high spatial variation in reproductive phenology and capable of breeding during pre-monsoon, monsoon, post-monsoon and winter. Water temperature is the most crucial environmental parameter influencing gonadal maturation and breeding. Generalized additive model (GAM) models revealed water temperature near 23–25 °C as optimum and threshold GSI above 3 units necessary for breeding. Pre-spawning fitness (Kspawn50) and size at 50% maturity (LM50) benchmarked through Kaplan-Meier survival fit estimates were in the range 1.27–1.37 units and 19–24.5 cm respectively. First maturity of females was encountered at 11.4 cm within the size range 7.2–28.5 cm. Egg parameters in mature-ripe females ranged between 0.29–0.80 mm (diameter), 0.05–0.19 mg (weight) and 5687–121 849 eggs (absolute fecundity). Mapping of climate preferendum through LOESS smoothing technique hinted water temperatures <20 °C and >32 °C to be detrimental for attainment of pre-spawning fitness while no dependence on rainfall was observed. Based on the climato-hydrological influence on breeding and regional trends of changing climate along river Ganga, we infer minimal climate driven changes in breeding phenology of this amphidromous fish species. Results of this study may serve as baseline information for future studies assessing climate driven changes and evolutionary adaptations in croakers from river Ganga.