Stock Status of Two Commercially Important Catfishes, Mystus gulio (Hamilton 1822) and Mystus cavasius (Hamilton 1822), in Relation to Environmental Variables Along the Lower Stretches of the River Ganga, India

Abstract

Mystus gulio and Mystus cavasius are small indigenous fish species (SIFs) found throughout the year at the various stretches of the river Ganga and contribute significantly to the commercial fishery. The current study was conducted with a total of 609 specimens of M. gulio with a total length ranging from 84 to 190 mm and 377 specimens of M. cavasius with a total length ranging from 51 to 232 mm, collected from eight selected sites of lower stretches of the river Ganga between July 2018 and October 2019 to analyse their growth, mortality, and exploitation status. The sample specimens’ length-frequency distribution, primarily taken from bag nets and set barrier nets used in artisanal fisheries, was assessed using the FiSAT II programme. For M. gulio, the estimated asymptotic length (L∞), growth coefficient (K), and initial condition factor (t0) were 183.23 mm, 0.31 yr−1, and −0.486 years, and for M. cavasius, these values were 246.23 mm, 0.19 yr−1, and −0.302 years, respectively. The estimates for the total (Z), natural (M), and fishing (F) mortality rates were 1.78, 0.49, and 1.29 yr−1 for M. gulio and 0.68, 0.33, and 0.35 yr−1 for M. cavasius, respectively. Both M. gulio (May to July) and M. cavasius (June to August) experienced a single spawning peak. The estimated exploitation ratio (E) for M. gulio was 0.72, which is higher than the optimal level of exploitation (Eopt) and the maximum level of exploitation (Emax). On the other hand, the E value for M. cavasius was 0.52, which means that it was exploited at the right level. The fishing pressure was found to be slightly excessive for the current stocks of M. gulio, which should be considered for proper management of the fishery in the river Ganga. The present study, the first of its kind, highlights the stock status of these two commercially important species and the management measures taken to revive the stock along the lower stretches of the Ganga in India. The environmental parameters of the lower stretches of the river Ganga show favourable conditions for the optimum growth of M. gulio and M. cavasius.

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