Relationship between uninflated swim bladder and skeletal anomalies in reared gilthead seabream (Sparus aurata)

Abstract

Abstract The higher mortalities and lower morphological quality of juveniles with a non-inflated swim bladder still remain a major problem in intensive farming. The aim of this study was to investigate a possible relationship between the presence of an abortive swim bladder and skeleton anomalies in gilthead seabream juveniles. A batch of 109 DAH (LS range: 16–47 mm) gilthead seabream was split into two groups on the basis of the presence (SB group)/absence (WSB group) of a normally inflated swim bladder, and processed for skeletal anomaly and meristic count analysis. The presence of pectoral fin anomalies and the absence of any clear-cut and sound relationship between abortive swim bladder and axis deviations characterize the WSB group. Rarer anomalies, such as scoliosis and lordosis in the pre-haemal vertebrae, kyphosis in the haemal vertebrae, pre-haemal and haemal vertebrae body anomalies, exclusively affected the WSB seabream. This result contradicts what is observed in other species, where abortive swim bladder is shown to cause axis deviation. The authors hypothesize that when gilthead seabream larvae with uninflated swim bladder encounter difficulty in maintaining the level in the water column, they have to overuse flapping of the pectoral fins (which appear more deformed in the seabream without swim bladder of this study). This determines a hyper-activity of the pectoral muscles, which then exerts an intense mechanical load on pre-haemal muscles and ossifying vertebrae. Vertebrae and axis anomalies in the pre-haemal and in haemal (in this study still rare in the WSB lot) regions may be later effects, as postural consequences due to the uninflated swim bladder.