Comparative morphometrics of sharpsnout seabream ( Diplodus puntazzo Cetti, 1777), reared in different conditions

Abstract

The same genetic stock of sharpsnout seabream ( Diplodus puntazzo), cultured in different conditions (lot A, monoculture tank; lot B, monoculture offshore cage; lot C, polyculture tank), was analysed using geometric morphometrics in order to detect changes in shape. Rearing in the offshore cage (lot B) had a significant effect on shape variation when compared to rearing in the two enclosed tanks (A and C). Fish from the tanks show a higher frequency (43.7% in lot A and 37.5% in lot C) of the so-called ‘goitred’ and ‘dorsal flat’ forms, their deformations shown by displacements in the corresponding landmarks of the infraopercular and dorsal areas. In contrast, the so-called ‘belly’ fish were more numerous in lot B (66.7%). These changes in shape are mostly related to a non-uniform variation (i.e. not due to shearing and dilation but localised in some body areas) and the differences were shown to be statistically significant between the lots. Finally, more than 90% of the variation in shape was left unexplained by the regressions of shape variables over size (expressed as weight in grams and centroid size). Change in shape does not seem to be strictly dependent on increasing size is therefore likely to be determined by culture conditions.