Skeletal anomalies analysis in Dicentrarchus labrax larvae selected for functional gas bladder.

Some Mediterranean hatcheries use selection techniques to eliminate fish lacking a functional swimbladder. The aim of this study is to make a morphological evaluation of fish selected by swimbladder sorting techniques. Experimental selection tests were performed on 456 90-d-old sea bass (SL = 27.4 ± 2.4 mm), produced under controlled conditions, anaesthetized with MS-222 Sandoz, and selected at three different salinities (37, 42, and 46ppt). The different salinity conditions under which sorting took place had no significant effect on separation efficiency, which was found to be 100% for the floating fraction and 99.21% for the sinking fraction. One-hundred-and-eightyone animals with swimbladder (S+) and 81 without ( S - ) were fixed in 4% formalin, stained, and observed in order to detect any cartilage or bone anomalies. In both groups of fish (S+ and S - ) , anomalies in the vertebral axis, the vertebrae, and in the fins, as well as the frequency of calculi in the terminal tract of the urinary duct were counted and compared using the x2 test. The S - group is characterized by: shorter standard length, higher frequency of anomalies of vertebrae and of the vertebral axis, and higher frequency of individuals with calculi in the terminal tract of the urinary ducts. Fin anomalies were found to be evenly distributed in both groups. The results led to the following conclusions: (1) morphological evidence confirms the effectiveness of the method in separating fish with swimbladders from those without; (2) the selection method does not provide a total guarantee of fish quality on a morphological basis: as many as 93.8% of the S+ fry were found to have skeletal anomalies.