Sex-ratio, reproduction and feeding habits of Pomadasys incisus (Haemulidae) in the Gulf of Tunis (Tunisia)

Abstract

         The reproduction and feeding habits of the Bastard grunt, Pomadasys incisus (Bowdich, 1825), in the Gulf of Tunis were investigated monthly from January to December 2003. An examination of the gonads of 463 specimens showed that the Bastard grunt is a gonochoric species and the sexratio wasn’t significantly different from 1:1. The monthly variations of the gonadosomatic index and the percentage of the different gonadal development stages revealed that P. incisus spawning period occurred from August to October. This species uses its energetic reserves contained in the liver and the muscles to assure gonadal maturation. The size at first maturity (L₅₀) was estimated at 15.33 cm for both sexes pooled. The stomachs examined showed a high vacuity index throughout the year (56.8%) and presented a significant difference between seasons. The stomach contents analysis revealed that P. incisus’ diet was especially constituted of crustacean species as well as benthic and planktonic organisms that belong to 19 taxa. The percentage frequency of occurrence (F) computed for Crangon crangon, Hyperoche sp. and Geryon longipes (the most abundant prey in the diet) showed significant differences among seasons (χ²_obs=31.228, 29.471 and 11.302 respectively, were superior to χ²_0.05).