Linking Fish Population Biology with LULC Dynamics: A Comparative Assessment of Puntius sophore in the Ganga and Punpun Rivers, India

Puntius sophore, a small indigenous fish species, has significance to the nutritional and livelihood security of rural communities in India. This study presents baseline data on the population dynamics, length-weight relationships (LWRs), and condition factors of P. sophore in two major rivers, the Ganga and Punpun in India, while assessing multi-decadal (1990-2023) land use and land cover (LULC) changes. Fish samples (506) were collected monthly from each of three landing sites from the river Ganga and Punpun. The results revealed that populations in both rivers have positive allometric growth, with length-weight relationship (LWR) equations of W = 0.0129 L^3.023 (Ganga) and W = 0.0079 L^3.169 (Punpun). The condition factors (Kc, Kn, Ka) were significantly higher (p < 0.05) than 1 in the Punpun River, indicating a favorable environment, while values < 1 in the Ganga showed higher ecological stress. The growth aspects (L∞ = 134.60 mm, K = 0.71 yr⁻¹ for Ganga; L∞ = 133.42 mm, K = 0.735 yr⁻¹ for Punpun) were analyzed by TropFish-R, showing a fast-growing species. Total mortality (Z) was higher in the Ganga (1.822 yr-1) in comparison to the Punpun (1.797 yr-1), though, exploitation rates (E < 0.5) confirmed under-exploitation. Length-based spawning potential ratio (LB-SPR) analysis revealed recruitment overfishing (SL < Lm), with a sustainable SPR of 0.40 in the Punpun and a depleting SPR of 0.32 in the Ganga. Although current fishing pressure is adequate, spatiotemporal LULC indicated that rapid urbanization and habitat fragmentation exhibit a substantial "squeeze" effect that adversely impacts aquatic ecosystems and poses a significant risk to spawning and feeding grounds of that ecosystem. Effective management approaches, including the execution of seasonal fishing bans during monsoon recruitment and the implementation of strict mesh-size standards, are essential for the conservation of wild populations and the protection of regional food supplies.