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

Abstract

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.