Comparative length-weight relationship and condition factor of hilsa shad Tenualosa ilisha (Hamilton, 1822) from freshwater, estuarine and marine environments in India

Abstract

The hilsa shad Tenualosa ilisha (Hamilton, 1822), is a commercially important and highly relished food fish. This paper presents the length-weight relationships (LWR) and condition factor of hilsa, throughout its geographical distribution in India. A total of 910 samples of T. ilisha, comprising 404 males and 288 females collected from various locations of east and west coasts of India were used for analyses. Heterogeneity in the LWR of males, females and pooled population was noticed. The regression coefficient (b) ranged from 2.07-3.68 for pooled, 0.75-3.03 for males and 1.78-2.97 for females. The coefficient of determination (R2) varied between 0.72-0.98 in pooled, 0.73-0.94 in males and 0.76-0.97 in females. Fulton’s condition factor (K) ranged from 0.47-3.05 in pooled, 0.47-1.63 in male and from 0.77-3.05 in female samples whereas relative condition factor (Kn) varied from 0.48-2.51 in pooled population, from 0.47-1.56 in males and 0.76-2.33 in females. Mean Fulton’s condition factor (K) ranged from 0.7-1.33 in pooled population, 0.92-1.28 in males and from 0.95-1.39 in females whereas the mean relative condition factor (Kn) varied between 0.98-1.04 in pooled population, 0.98-1.04 in males and 0.98-1.03 in females. These parameters (b, K, Kn) have been found useful in evaluating the well-being of different populations of this species. Most of the populations under study showed concordance to ideal value of b, thereby indicating isometric growth. However, significant negative allometric growth was observed for pooled samples from Padma, Hoogly and males from Padma and significant positive allometric growth was observed in the pooled samples collected from Hoogly. Comparative study of recent data with the decadal old data (1999-2000) revealed differences in mean size of the fish. This study also indicates overexploitation of the species in the recent years, which might be due to intensive fishing efforts.