The aim of this work is to study the variation of the global chemical composition of six fish species (Lithognathus mormyrus, Mullus barbatus, Mullus surmuletus, Pagellus erythrinus, Pagrus caeruleostictus and Dentex maroccanus) caught by the trawl of the Gulf of Gabès (Mediterranean Sea). The variations of the chemical contents of the fish as a function of size, sex, organs and parts of the muscle were examined between December 2005 and May 2006. ANOVA indicated that the global chemical composition was significantly affected by two factors: species and body locations (parts of the muscle). The correlation matrix established between the chemical contents showed two highly significant correlations (fat–moisture and protein–ash). The discriminant analysis allowed the distribution in the space of fish species into five groups according to their moisture, proteins, fat and ash contents. The analysis of the fat content in the parts of the fish body revealed the presence of a concentration gradient.