The effect of invertebrate diets on lipids, fatty acid composition and physiological condition of pike larvae (Esox lucius)

The present study tests two invertebrate diets for pike larvae reared in floating cages. One diet contained mainly copepods and cladocerans such as Eucyclops serrulatus and Bosmina longirostris, while the other diet contained Eucyclops serrulatus together with a small proportion of large Chydoridae and chironomid larvae. During the first days of the experiment, the amount of food distributed to the larvae was insufficient (9-17.1 prey per larva and per day) and led to an increase in the mortality. Triacylglycerol contents of fry were low and dietary fatty acids were either catabolised or, concerning PUFA such as 22:6(n-3), incorporated into phospholipids. From day 13 to the end of the study (day 22), the most abundant diets distributed were accompanied by an increase in triacylglycerol PUFA and in triacylglycerol contents of larvae. During the same period weight and length growth were better for larvae reared on the copepod plus Chydoridae and chironomid diet, than for larvae reared on the copepod and Bosmina diet. The use of a lipid condition index based on the triacylglycerol/sterol ratio suggested that Chydoridae and chironomids positively influenced the growth and nutritional condition of larvae. The effects of prey type in terms of PUFA composition on pike larvae are discussed.