Temperature effects on cranial deformities in European sea bass, Dicentrarchus labrax (L.)

Summary The present study investigates the effect of water temperature on the development of deformities during embryonic and larval stages of European sea bass, Dicentrarchus labrax (L.). Two temperature conditions were examined in duplicate by studying the presence of skeletal deformities in a sample of 45 to 51 fish taken from each population at the end of the rearing trials [20–23 mm total length (TL)]. The results indicated that water temperature during the embryonic and larval phase has significant effects on deformation of the branchiostegal rays (P   0.05). At 15°C, 27.2–33.4% of the examined fish had branchiostegal rays of abnormal shape and/or orientation, whereas at 20°C this deformity had a frequency of only 4.0–4.1%. The frequency distribution graph of branchiostegal counts demonstrated a significant deviation in the deformed fish from the normal (seven rays on each side of the body) phenotype at both temperatures tested. This deviation was mainly expressed as a lack of one to four rays (56.7% of deformed fish), or the formation of one extra ray (26.7% of deformed fish) (P < 0.001, G-test). The results are discussed in respect to the possible mechanisms of temperature effects on the development of skeletal deformities.