UTTAR PRADESH JOURNAL OF ZOOLOGY

Length-weight relationship is considered a significant biological parameter in fisheries because it determines the growth rate, maturity timing, taxonomic distinctions between species, population dynamics, and habitat suitability. The relative condition factor can also be determined using the fish’s actual weight and experimental weight obtained from the length-weight relationship. It gives a numerical representation of a fish's state, including its level of health, robustness, plumpness, and fatness. The objective of the present study is to assess the length-weight relationships and relative condition factor of Mystus tengara (Hamilton, 1822) from the Rupnarayan River of W.B. From January 2025 to December 2025, 311 specimens were collected (comprising 193females and 118 males) using conventional fishing equipment. Female specimens’ total length ranged from 5.2-12.9 cm and weight 2.3-19.9 gm, while male specimens' length ranged from 7.5-10.9 cm and weight 2 -13.3 gm. Female dominated males in number and size. Length-weight relationship analysis indicated a strong correlation (r) and high growth performance. The female exhibits positive allometric growth (b=3.102), but the male exhibits negative allometric growth (b=2.97), and the combined population demonstrates (b=3.03), suggesting an optimum climate condition for fish growth. Relative condition factor (Kn) value ranges from 1.02±0.19 for females, while for males, 1.01±0.13, and 1.03±0.20 for the combined population. ‘Kn’ value higher than one (1) signifies a better condition of fish in a specific environmental state. Overall, the findings indicate that the environment of the Rupnarayan River is suitable for the healthy growth and development of Mystus tengara.