Sex ratio of Nemacheilus multifasciatus (Hillstream Loach) in the Heval River of Garhwal Himalaya, Uttarakhand, India

Nemacheilus multifasciatus is a hillstream loach that contributes to the stability of Himalayan ecosystems and supports local subsistence fisheries. This study aimed to evaluate the sex ratio of the N. multifasciatus in the Heval River, a tributary of the holy river Ganga, across temporal (monthly, seasonal) and size class scales and to examine its deviation from the expected 1:1 proportion. A total of 253 fish specimens were collected from 2023 to 2025 and examined to assess the sex ratio by month, season, and 0.5 cm length groups and to determine the stock percentage in each size group using chi-square tests for deviation from parity. Monthly sex ratio (male: female) ranged from 1:0.86 (November) to 1:1.43 (August), while seasonal value varied from 1:1.06 in autumn to 1:1.30 in summer; none of these temporal differences were statistically significant (p>0.05). Size-wise sex ratios showed stronger deviations, from 1:0.17 at 5.1-5.5 cm to 1:8.00 at 8.6-9.0 cm, with significant differences among length groups (p<0.05). The highest stock percentage (18.18%) was observed in the 7.6-8.0 cm size group, and the lowest (0.79%) in the 9.1-9.5 cm group, with an overall sex ratio of 1 male:1.18 females for the population. These observations and overall analysis indicate a slight female bias and size-dependent variations in the sex ratio of this hillstream loach, N. multifasciatus, with potential implications for population dynamics and management.