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 th e experiment, the amount of food distributed to the larvae was insuffi cient (9-17.1 prey per larva and per day) and led to an increase in th e mortality. Triacylglycerol contents of fry were low and dietary fatt y 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 i ncrease in triacylglycerol PUFA and in triacylglycerol contents of lar vae. During the same period weight and length growth were better for l arvae 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 th at Chydoridae and chironomids positively influenced the growth and nut ritional condition of larvae. The effects of prey type in terms of PUF A composition on pike larvae are discussed.