LIPID CLASS AND FATTY-ACID COMPOSITION OF PLANKTIVOROUS LARVAL PIKE ESOX-LUCIUS LIVING IN A NATURAL POND

This study was undertaken in a pond used for natural spawning of pike. Zooplankton and pike larvae were sampled using a horizontal haul net (120 mum or 1 mm mesh size) through the aquatic vegetation. Among the different class sizes of larvae, one cohort was isolated (11.1 mm less -than-or-equal-to L less-than-or-equal-to 46 mm), in which larval pike first fed on small Cyclopoids then switched to Cladocerans until they fed on insect larvae. Length (1.2 nun/day) and weight growth were fou nd to be fast. Between day 8 and day 13 of exogenous feeding there was a marked decrease of reserve lipids of larvae. This decrease coincide d with a lower growth and seemed to be ascribable to changes from Cycl opoid (60.4 % of ingested prey) to 2 species of Cladoceran (42.4 % and 36.4 % of ingested prey), in the feeding sequence of larvae. Pike pro bably found difficulties in capturing Cyclopoid and digesting Cladocer ans as their alimentary canal was not completely developed. After day 13, Cladoceran digestibility was good as the S-bend gut was formed, wh en triacylglycerol content of larvae increased until the experiment ce ased. As indicators, of good growth, we detected increasing amounts of phospholipids throughout the whole study. The fatty acid composition of larval triacylglycerols appeared to be very similar to the composit ion of zooplankton lipids. Dietary fatty acids could have been incorpo rated whithout modification into triacylglycerols and into phospholipi ds possibly with limited elongation/desaturation. The results suggest that pike larvae require both (n-3) FA and (n-6) FA.