The Length-Weight Relationship, Condition Factor and Reproductive Biology of Pseudotolithus (P) senegalensis (Valenciennes, 1833) (croakers), in Tombo Western Rural District of Sierra Leone

Abstract

The length–weight relationship (LWR), condition factor (K), sex ratio, gonadosomatic index (GI) and hepatosomatic index (HI) of 412 specimens of Pseudotolithus senegalensis (Valenciennes, 1833) from Tombo a coastal fishing community in the western rural district of Sierra Leone were studied for twelve months. Samples used for the study were collected from the catches of artisanal fishers and measurement of length and weight of samples were done in situ using the facilities of the Ministry of Fisheries and Marine Resources. Samples for reproductive study were preserved in ice box and were taking to the laboratory of the Department of Aquaculture and Fisheries Management, Njala University, Sierra Leone for analysis. The parameters "a" and "b" of the length-weight relationship were estimated using the equation described by Ricker (W = aLb) while the condition factor was calculated using Fulton`s equation (K = W100 L3). The reproductive biology of the fish was estimated using Gonadosomatic index (GSI) and Hepatosomatic index (HI) following the method of Ekanem et al. [16] The combined LWR for both sexes showed that a,b and r values were 6.27, 3.25 and 0.95, respectively. The r – values obtained show a strong linear relationship between the length and weight of the species. The length/weight relationship indicated allometric growth for males and isometric growth for females. The condition factor (K) values varied from 0.64 – 1.0 with a mean I value of 0.98. The species exhibited a positive allometric growth pattern. The sex ratio of males to females was 1:1.08 and was not significantly different from the expected 1:1 ratio. Estimation of GSI and HSI was carried out from December, 2010 to May, 2011 to determine the spawning behaviour of P. Senegalensis. The mean value of GSI in December and March - May indicated that these are the two peak spawning periods for the species Gonado-somatic index ranged between 1.1% and 2.8% in the females. The results of this study revealed that P. Senegalensis does not have obligatory spawning month but exhibit multiple spawning behaviour. The length-weight relationships and condition factor of the study indicated that the environment is suitable for the survival and reproduction of P. senegalensis. Sustainable management of the species, however, requires that the environment be protected against anthropogenic pollution and also imposition of closed fishing season especially during the two peak spawning periods is recommended to enable the species to recruit effectively.

Keywords: Length-weight, Pseudotolithus senegalensis, reproductive biology, Sierra Leone