Genetic parameters of the upper-jaw abnormalities in Gilthead seabream Sparus aurata

The development of skeletal abnormalities is a frequent problem of quality in finfish hatcheries, resulting from unfavourable environmental conditions, often under the control of genetic background. In the present study, the heritability of jaw abnormalities in Gilthead seabream was estimated at the end of the larval rearing phase (39 dph, days post hatching). All larvae came from eggs obtained by mass spontaneous spawn of a common brood stock of a commercial hatchery. Skeletal abnormalities were examined after the double staining of the larvae for bone and cartilage. Macroscopically, three abnormality types were recorded in the studied larvae, pugheadness (Pug, 6.7%), lateral displacement of the upper jaw (LdUj, 2.3%) and crossbite (Crbt, 0.9%). The microscopic examination of the specimens revealed the frequent presence of internal abnormalities (e.g. fusions, size reductions, bending) which had not any clear effect on the external morphology of the fish (silent abnormalities). Each stained larva was genotyped and parentally assigned. Heritability estimates were insignificant for the three types of gross, externally-visible, abnormalities of the jaws (Pug, LdUj, Crbt). On the contrary, significant heritabilities were estimated for the internal abnormalities which are associated to LdUj (e.g. fusion of maxillaries with pre-maxillaries, 0.22 ± 0.06). Interestingly, the consideration of all the abnormalities of the upper jaw as a uniform trait resulted to the estimation of insignificant heritabilities, and therefore to the masking of the significant genetic component of the LdUj abnormality. Results are discussed in respect to their potential value for the selective breeding programs of Gilthead seabream.