Length-Weight Relationships and Food Preference of Two Coastal Marine Fishes, Galeoides decadactylus (Polynemidae) and Sphyraena sphyraena (Sphyraenidae) off Cape Coast, Ghana

Abstract

The food and feeding habits of most commercially important marine fish species in Ghana had not been studied. The aim of the paper was to study the diet spectrum of two coastal fishes of Ghana; Galeoides decadactylus (Polynemidae) Bloch, 1795 and Sphyraena sphyraena (Sphyraenidae) Linnaeus, 1758, both of tropical fish species. Fish samples were obtained in 2011 from sandy beaches near Cape Coast township in the Central Region of Ghana, noted for beach seining. Length-weight measurements were taken from well-preserved fish specimens from which stomachs were extracted for the analysis of the food contents, using frequency of occurrence, numerical and gravimetric methods, as well as index of relative importance. The length-frequency analysis showed a size distribution with a modal size of 11.0–13.9 cm for both species. The length-weight relationships for both fish species showed strong correlation between the weight and length with correlation coefficient (r²) and exponent b for Galeoides decadactylus as 0.9869 and 2.9893, and that for Sphyraena sphyraena as 0.9861 and 2.9094, respectively. Juvenile shrimp and fish fry formed the bulk of the food items in the stomachs of the two fish species. Juvenile shrimps occurred in 77.18% of the stomachs observed for G. decadactylus and accounted for 80.20% of the total number of the food items whilst comprising 63.14% of the weight of food consumed. That of S. sphyraena was, respectively, 66.7% by frequency, 87.0% by numbers and 96.3% by weight. Juvenile shrimp had the highest IRI in the diet of G. decadactylus whereas in S. sphyraena fish fry recorded the highest IRI. Literature evidence showed that the diet spectrum and aspects of growth of the two fish species reported elsewhere in the tropics were comparable to that off the coast of Cape Coast despite the differences in geographical location. The findings in this study will contribute to the knowledge gap on the diet of most commercially important fish species in Ghanaian waters.