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 degrees C) on hatching, development and survival of yolk-sac larvae of European hake, Merluccius merluccius, was studied. At 22 degrees 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(circle)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(circle)C respectively, reaching a maximum length of 4.3 mm at 10.5(circle)C. Metabolic indices such as: lowest threshold temperature (T-0); effective larval development (D-eff degrees); 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.