Effects of rearing conditions on skeletal anomalies typology and frequency in gilthead seabream Sparus auratus juveniles.

This study analyzed different lots of gilthead seabream juveniles outcoming from the same egg batch, but reared under different (intensive vs semi-intensive) conditions aimed at: (1) quantitatively and qualitatively analyzing whether differences in skeletal elements (shape and number) arise; (2) to investigate if a relationship between skeletal bone tissue/ossification and some environmentally-induced malformation exists; and (3) identifying the best practices for seabream larval rearing in order to obtain lower deformity rates. A total of 981 reared juveniles of gilthead seabream were analysed, among which 721 were from a commercial hatchery located in Northern Italy (Valle Figheri, Venice, Italy), and other 260 were obtained from the Hellenic Center for Marine Research (Iraklion, Crete, Greece). These individuals were from 4 different eggs batches (Groups 1-4), for a total of 10 different lots. Each egg batch/group was split after hatching in two lots, and reared with two different methodologies, intensive and semi-intensive rearing. Some lots (Group 3: INIT19, INIT18, LVIT04, LVIT05) were sampled at two different ages. Semi-intensive lots were reared under two different methodologies: Large Volumes (sensu Cataudella et al., 2002)and Mesocosm (sensu Divanach and Kentouri, 2000). All the samples were analyzed (whole mount staining) for skeletal anomalies and variation in meristic counts. Lower severe skeletal anomalies incidences and meristic counts variability were found in all the semi-intensively reared lots, with significant higher capacity of Large Volumes of ameliorating anatomical quality of juveniles than Mesocosms. In all the semi-intensive lots, the bones undergone intramembranous ossification showed constant lower incidences of malformations whilst endochondrally and perichondrally ossifying skeletal elements did not always exhibit the same clear pattern. This study was funded by the Italian Ministry for Agriculture, Food and Forestry Policy (Law 41/82).