Sex-Based Variations in Length–Weight Relationship and Condition Factor of Heterotis niloticus from Kalgwai Reservoir

Abstract

The present study investigated how sex influences the length–weight relationship (LWR) and condition factor (K) of Heterotis niloticus inhabiting the Kalgwai Reservoir in Northwestern Nigeria from January 2022 to December 2023. A total of 120 specimens, comprising equal numbers of males and females, were randomly collected from three sampling stations using a combination of gill nets (25–50 mm mesh sizes), cast nets and longlines. Total length and body weight were recorded following established biometric procedures, and sex was identified through gonadal examination. Analysis of the log-transformed length–weight data revealed that males had b-values ranging from 0.35 to 1.21, with a mean of 1.21, whereas females exhibited a wider range of 0.03 to 1.95 and a higher mean value of 1.95. The combined dataset produced an average b of 1.42. In all cases, the regression coefficient (b) was below the theoretical cube value (b = 3), signifying negative allometric growth, where increase in length outpaces gain in weight. The Fulton’s condition factor (K) differed between sexes, with males averaging 0.70 and females 1.20, while the overall mean stood at 0.90. The relatively higher K values recorded in females indicate a better physiological state, possibly linked to energy accumulation for reproduction, whereas the low values observed in some males point to potential nutritional stress. These outcomes emphasize the importance of sex in determining the growth pattern and well-being of H. niloticus and provide essential reference data for the management and aquaculture development of the species within the Kalgwai Reservoir.