Growth, oxygen consumption and activity of juvenile turbot (scophthalmus maximus L.) reared under different temperatures and photoperiods

Juvenile turbot (5–125 g) were reared under two experimental temperatures: 10°C and 16°C, and three experimental photoperiods: LDN (natural photoperiod), LD 16:8 (16 h light: 8 h darkness), LD24:0 (continuous light), to study effects of temperature and photoperiod on growth, activity and oxygen consumption. Growth was strongly affected by temperature and was higher at 16°C than at 10°C. Continuous light had a growth-promoting effect at 10°C from mid-December to late March, while at 16°C this effect was restricted to December and January. A seasonal change in the condition index was found. The groups reared in continuous light had higher condition indices in winter. The experimental groups held at 16°C had higher O₂ consumption than those at 10°C. The LD24:0 groups invariably had a higher overall O₂ consumption than did the LDN and LD16:8 groups, the differences being caused by reduced O₂ consumption in the latter groups during darkness. The LD24:0 groups displayed higher activity than the LDN groups, in which activity was very low at night.