The relationships of total length (Lt ) to girth at opercula (Gope) and maximum girths (Gmax) were estimated for 39 and 22 fish species, respectively, captured off the Portuguese coast between Povoa do Varzim and Santo Andre (38º05’54’’–41º15’36’’N and 8º46’54’’–9º31’13’’W). The data were collected between April 1994 and September 1995. The best-represented family was Sparidae (five species), followed by Soleidae and Triglidae (four species each). Gmax and Gope increase linearly with length for all species, all r2 values being statistically significant (P < 0.01) and higher than 0.81. When Gope and Gmax were plotted against length for all species combined, three groups were identified, corresponding to general girth–length relationships: G1 = 1.408 + 0.238 • Lt, G2 = 2.455 + 0.328 • Lt and G3 = 0.72 + 0.60 • Lt for opercula girth and G1 = 3.402 + 0.195 • Lt, G2 = 2.211 + 0.374 • Lt and G3 = -2.514 + 0.717 • Lt for maximum girth. These groups correspond to different body shapes of fishes: G1-round, G2-torpedo-form and G3-compressed body.