ABNORMAL SWIMBLADDER DEVELOPMENT AND LORDOSIS IN SEA BASS (DICENTRARCHUS-LABRAX) AND SEA BREAM (SPARUS-AURATUS)

Many types of skeletal malformations are found in species reared in intensive conditions. Lordosis, characterized by a more or less acute V-shaped spine, is the most common. It may be congenitally or post-natally induced. Poor rearing conditions are usually the cause of postnatal lordosis. A correlation between the appearance of lordosis in 0.7-4 g juvenile Dicentrarchus labrax and Sparus auratus and the lack of functional swimbladders was found in larval forms of both species. Lordosis was present in all fish which were forced to swim against a current of at least 20 cm/s, while only 20-30% of fish reared in static waters were affected, thus suggesting a mechanical cause of this deformity. Spinal curvatures were mainly in the area of vertebrae 14-15 which is the area where muscle pressure is highest during swimming. The curvature of the deformed fish increased with weight and from less than 10-degrees in 0.7-g fish to 60-degrees in 4-g sea bass and 120-degrees in 150-g sea bream. Late swimbladder inflation was observed in S. auratus of about 7 g and over. However, late swimbladder inflation did not reduce spinal curvatures in fish with chronic lordosis starting at the larval phase.