The effect of temperature on the development of yolk‐sac larvae of European hake ( Merluccius merluccius L.) under laboratory conditions

The effect of temperature (10, 13, 16, 19 and 22°C) on hatching, development and survival of yolk‐sac larvae of European hake, Merluccius merluccius , was studied. At 22°C the experiment was suspended because all eggs died a few hours after incubation. Five morphological indicators of larval development (standard length – SL , yolk‐sac volume – YSV , oil globule diameter – OD , body height – BH and body wet weight – BW ) were analysed. SL , YSV , OD and BW of newly hatched larvae were biggest in size and weight at low temperatures ( P  < 0.05). Throughout the experiments, the rates of changes in SL , YSV and OD varied with temperature ( P  < 0.05). By contrast, BH and BW remained constant and did not show significant relationship with the effect of temperature ( P  > 0.05). The potential model showed that the SL growth rate varied from 0.05 to 0.08 mm day −1 from 10.5 to 19.5°C respectively. However, at all temperatures two growth phases were identified: a rapid growth phase followed by a slow one. Rapid growth rate in length and depletion in yolk‐sac and oil globule occurred at high temperatures. After total YSV and OD consumption (death by starvation), larvae died between 8 and 14 days at 19.5 and 10.5°C respectively, reaching a maximum length of 4.3 mm at 10.5°C. Metabolic indices such as: lowest threshold temperature ( T 0 ); effective larval development ( D eff ∘ ); cumulative thermal units ( TC ) to complete larval development; the temperature coefficient on growth rate in length ( Q 10 ) and the condition factor ( K ) were also studied.