Influence of salinity and linoleic or ¿-linolenic acid based diets on ontogenetic development and metabolism of unsaturated fatty acids in pike perch larvae (Sander lucioperca)

Abstract

Combinations of nutritional requirements and husbandry rearing conditions during early ontogeny are poorly studied in pikeperch (Sander lucioperca). The substitution of marine oils with vegetable oils has reduced stress tolerance and caused neurophysiological changes in pike perch larvae, but effects of environmental cues are limited. Saline water influences on a range of physiological functions during early fish larval ontogeny and may affect FA metabolism, − elongation and desaturation - activity when given diets limited in LC PUFAs, but rich in shorter chain n-3 or n-6 PUFAs. Consequently, live Artemia differing in 18:2n-6 (LA) and 18:3n-3 (ALA) content by enrichment with sunflower oil (SFO) or linseed oil (LO) were fed to 10 days post hatch (DPH) larvae and reared up to isosmotic salinities (0, 5, 10 ppt) until 30 DPH. Larval tissue FA composition was examined at 15, 25 and 30 DPH. Besides, an in vivo assay was performed on 20 DPH larvae with 14C labelled FA including LA; ALA; 20:4n-6 (ARA); 20:5n-3 (EPA) or 22:6n-3 (DHA) to establish FA incorporation and metabolism. At 30 DPH, performance, digestive enzymatic activity, eicosanoid activity, skeletal anomalies and stress sensitivity were further evaluated. Results on larval FA profiles suggest a low desaturation and elongation capability over LA and ALA, with no significant effects of salinity or larval age on modulation of unsaturated fatty acid metabolism. In vivo assays revealed that regardless of salinity or diet, pikeperch possess a marked specificity to incorporate ARA and EPA compared to a poorer incorporation of DHA. Larvae exposed to a confinement stress test caused high acute mortality in all experimental groups except for a control group fed with Artemia enriched by a commercial DHA Selco emulsion. Growth performance was not significantly affected by salinity or dietary enrichment with SFO or LO, but influenced on larval enzymatic activity of pepsin, aminopeptidase, trypsin and alkaline phosphatase, while lipase activity was not significantly affected. Increased saline conditions significantly decreased hormonal prostaglandin eicosanoid PGE2, PGE3 activity with the highest activity at 0 ppt. The prevalence of severe skeletal anomalies was generally high, affecting over 75% of the larval population with negative effects by increase in salinity. The incidence of anomalies was higher on endochondral bones, namely maxillary, ranging from 58 to 83% of the population. These results agree well with those from expression of sox 9 and twist2 genes; involved in chondrocyte ossification and differentiation.