Environmental determinants of haemal lordosis in European sea bass, Dicentrarchus labrax (Linnaeus, 1758)

We tested the effect of water-temperature during the larval phase on sea bass sensitivity to current-induced lordosis. During larval rearing phase, fish were subjected to two different water temperatures (15 or 20 degrees C), with the rest of the rearing parameters remaining identical between the different populations. During the pregrowing phase, the different populations were subjected to four different water-current velocities (WCV), with the rest of the environmental conditions remaining common. At the end of the pregrowing phase (43.5 +/- 0.8 mm TL), lordosis was more frequent in fish that developed at 20 degrees C (p < 0.05), independently of the WCVs applied. The anatomic analysis of the deformed fish revealed a significant effect of early developmental temperature on the severity of the deformity, with the 15 degrees C populations showing the lower severity in respect to the angle of lordosis and the number of affected vertebrae (p < 0.05). Two weeks of exposure to WCVs (24.0 0.8 mm TL) resulted in 15 degrees C populations presenting the lower incidence of lordosis and the higher incidence of normal fish in all WCVs, except 50%, tested (p < 0.05). At this stage, WCV had a clear effect on lordosis development in populations coming from both developmental temperatures (p < 0.05), although at 15 degrees C these effects were more pronounced. Fish that developed at 20 degrees C showed significantly higher incidence of deformed vertebral centra and arches than those developed at 15 degrees C (p < 0.05). These early anatomical signs were evident in samples taken at the end of the larval rearing phase (15.7 +/- 1.0 mm TL), as well as I week after the onset of exposure to WCVs (21.4 +/- 0.6 mm TL). In both cases, their incidence was significantly higher in fish that initially developed at 20 degrees C than at 15 degrees C. (c) 2005 Elsevier B.V. All rights reserved.