Effects of temperature on yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus L.)

Larvae of Atlantic halibut were incubated at five different temperatures (4, 6, 8, 10 and 12 degrees C) from hatching onwards (Experiment 1), and at 4 degrees C for a period of 0, 10, 20, 30 or 40 days before the temperature was increased to 6 degrees C or 8 degrees C (Experiment 2). Both experiments were terminated at time of first feeding, 230 day-degrees (d degrees) after hatching. In Experiment 1, larval survival was significantly lower at 12 degrees C, and the yield of normally developed larvae dropped significantly when larvae were incubated at 6 degrees C or higher. When larvae were incubated for different periods at 4 degrees C (Experiment 2), the number of days at 4 degrees C had a significant effect on larval survival and the frequencies of functional larvae, jaw deformations and yolk sac oedema, while the temperatures in the second period (6 degrees C or 8 degrees C) had no significant effect on the same traits. Frequency of normally developed larvae increased with increasing number of days at 4 degrees C while the survival rate tended to decrease with increasing number of days at 4 degrees C. Myotomal height, larval dry weight, yolk sac volume and feeding incidence were less influenced by the incubation temperature in both experiments. The results demonstrated that the development of abnormalities like gaping jaws and yolk sac oedema in halibut yolk sac larvae can be associated with high temperatures and presence of different temperature tolerances at different developmental stages. (C) 1997 Elsevier Science B.V.