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 °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 °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 °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 °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 °C these effects were more pronounced. Fish that developed at 20 °C showed significantly higher incidence of deformed vertebral centra and arches than those developed at 15 °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 1 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 °C than at 15 °C.