Assessing vulnerability of freshwater minnows in the Gangetic floodplains of India for conservation and management: Anthropogenic or climatic change risk?

Abstract

Minnows are the most ignored yet indispensable group of freshwater fishes in Asian inland waters. The reproductive resilience of minnows facing climatic variability, using a wetland inhabiting species Amblypharyngodon mola (Mola carplets) in lower Indo-Gangetic floodplains, was validated. Results revealed that spawning decision in females (threshold gonadosomatic index 5 units) is neither cued by water temperature nor rainfall. They can maintain pre-spawning fitnes≥s (condition factor 1.12–1.25 units) within a broad temperature (22–33 ◦C) and rainfall (0–800 mm) window by active feeding, thus no risk of skipped spawning decisions while facing future climatic variabilities. Present breeding phenology (May-December) might have prolonged in the recent decade, especially the tail-end, concomitant with increasingly hot and rainy monsoon (May-August) and warmer post-monsoon months (September-December). Minnows are expected to prosper in a future climatic scenario, contributing to ecosystem balance (algal grazers) and regional food security. Female first maturity (♀ puberty) was encountered at 4.7–5.1 cm total length, hinting at a probable increase in the recent decade. Climate-favored prolonged recruitment window, in absence of extreme fishing pressure (currently), might have led to such pattern. However, this state might be temporary and labile. Minnows may soon get altered to earlier puberty (=warning sign of stock collapse) if fishing pressure intensifies under a reproductively favoring climate progression. Threshold body girth for spawning females was estimated at 3.2–3.4 cm ( + 17% than non-breeding ones). Fishing nets having mesh sizes (=total circumference) at least > 32–34 mm will most likely be the key to minnows’ endurance or survival in the coming decades.