Lipid class and fatty acid composition of planktivorous larval pike Esox lucius living in a natural pond

Abstract

This study was undertaken in a pond used for natural spawning of pike. Zooplankton and pike larvaewere sampled using a horizontal haul net (120 μm or 1 mm mesh size) through the aquatic vegetation. Among the different class sizes of larvae, one cohort was isolated (11.1 mm < L < 46 mm), in which larval pike first fed on small Cyclopoids then switched to Cladocerans until they fed on insect larvae. Length (1.2 mm/day) and weight growth were found to be fast. Between day 8 and day 13 of exogenous feeding there was a marked decrease of reserve lipids of larvae. This decrease coincided with a lower growth and seemed to be ascribable to changes from Cyclopoid (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 probably found difficulties in capturing Cyclopoid and digesting Cladocerans as their alimentary canal was not completely developed. After day 13, Cladoceran digestibility was good as the S-bend gut was formed, when triacylglycerol content of larvae increased until the experiment ceased. As indicators, of good growth, we detected increasing amounts of phospholipids throughout the whole study. The fatty acid composition of larval triacylglycerolsappeared to be very similar to the composition of zooplankton lipids. Dietary fatty acids could havebeen incorporated whithout modification into triacylglycerols and into phospholipids possibly with limited elongation/desaturation. The results suggest that pike larvae require both (n-3) FA and (n-6) FA.