Muscle growth in cod larvae in response to dietary HUFA ratios

Larvae of cod (Gadus morhua L.) were fed rotifers (day 5-20) and Arte mia nauplii (day 17-31) that were short term enriched, so that the DH A:EPA rat high (~2.0) or low (~0.2). The temperature was 8°C at hatch ing and was gradually increased to 12°C during the yolk sac stage. Tr eatment 1 (T1) received a high DHA:EPA ratio in both the rotifer and the Artemia phase, treatment 2 (T2) received a high ratio in the roti fer phase and a low ratio in the Artemia phase and treatment 3 (T3) g ot a low ratio in the rotifer phase and a high ratio in the Artemia p hase. In this communication we report on the effect of these treatmen ts on survival, increase in dry weight and muscle growth. At the end of the experiment T1 had a 5% higher survival than T2 and T3. During the rotifer phase the relative growth rate was 8% per day in T1 and T2, but only 5% in T3. During the Artemia phase T1 and T2 grew by app roximately 14% per day and T3 grew by 10% per day. T3 therefore had a significantly lower dry weight than T1 and T2 at day 31. A reduced D HA:EPA ratio in the rotifer phase therefore seemed to have a negative effect on growth in later stages, whereas this effect was not seen w hen the low DHA:EPA ratio was given in the Artemia phase. Morphomet ric analyses of histological sections from the swimming muscle indica ted that the reduced larval growth in T3 was related to a lower propo rtion of white muscle fibres of a certain size. Also, at day 31 the w hite muscle fibres of larvae from T1 had a significantly higher volum e fraction of myofibrils than T3. This could explain why the latter g roup had a lower dry weight at this stage.