Studies on some reproductive aspects of &lt;i&gt;Pseudotolithus elongatus&lt;/i&gt; in Cross River estuary, Nigeria

Sunday Ben Ekanem,Mfon Michael Ekere,Marilyn Joan Achima

doi:10.3989/scimar.2004.68n2265

Abstract

To determine the spawning time of Pseudotolithus elongatus the Cross River estuary, ovarian development, egg diameter, gonadosomatic index (GSI) and hepatosomatic index (HSI) of the female fish were studied from January to December 1998. All ovary developmental stages, including the spawning stage, were present every month, which indicated year-round spawning. High mean values of GSI and egg diameter in December-March and July-September indicated these as the two peak spawning periods for the species. The egg diameter ranged from 1 µm to 590 µm. The highest number of eggs found in an individual fish was 808911. Absolute fecundity of the species in The Cross River estuary can be calculated in relation to standard length using the formula F = 17557SL 0.768 or F = 45532W 0.277 in relation to weight. There were evidences to suggest that the species is an asynchronous partial spawner. The stock might be effectively conserved by the imposition of a closed fishing season during the two peak spawning periods.

Highlights

The croakers or Pseudotolithus spp. are sciaenids found along the West African coast fromSenegal to Gabon (Fisher et al, 1981) where they are exploited by both the artisanal fishery (UweBassey, 1988) and the industrial fishery
All five stages of gonad development were present every month of the year and the monthly abundance of the different gonad developmental stages is presented in TABLE 1. – Monthly percentage occurrence of different egg developmental stages in the gonads of Pseudotolithus elongatus of the
All-year-round spawning confirms that recruitment takes place throughout the year, as stated by Etim et al (1994); the peak spawning periods speculated by these authors coincides with the findings in this study

Summary

Introduction

The croakers or Pseudotolithus spp. are sciaenids found along the West African coast from. Senegal to Gabon (Fisher et al, 1981) where they are exploited by both the artisanal fishery (UweBassey, 1988) and the industrial fishery Important Pseudotolithus species found here are P. elongatus, P. typus and P. senegalensis. Croakers are important food fish for Nigeria as they constitute about 40% of the total fish landing on the Nigerian coast (Gaffer, 1994). Pseudotolithus elongatus is the most economically important species in the Cross River estuary, where it constitutes 43.4% of the total catch by artisanal fishermen (Etim et al, 1994)

Methods

Discussion

Conclusion