This study was carried out to evaluate the effects of dietary phospholipid on the development and rearing performance of pikeperch (Sander lucioperca) larvae. From day 10 post-hatching, fish larvae were weaned onto three isoproteic and isolipidic formulated diets with different phospholipid (PL) levels: 1.4 (PL1), 4.7 (PL5) and 9.5% (PL9) of dry matter, as soybean lecithin. Neutral lipid (NL) with inversed gradient was incorporated in diets. Survival, growth and deformities were monitored until day 34 post-hatching, as well as intestinal enzyme activities, leucine alanine peptidase (leu-ala), aminopeptidase N (AN) and alkaline phosphatase (AP), which were used as indicators of digestive tract maturation. This study showed that PL supplementation significantly improved growth but not survival. The increase in dietary PL from 1.4 to 9.5% led to a 50% increase in larval final weight suggesting that high PL levels are needed during larval stages of pikeperch. The incidence of deformities was not affected by dietary phospholipid level. The specific activity of brush border membrane enzymes (AN and AP) increased with dietary phospholipid levels, indicating an earlier or more efficient maturation of digestive structures. A gut maturation index based on the ratio of segmental activity of the brush border membrane enzyme AP related to segmental activity of a cytosolic enzyme, leu-ala, was significantly higher in PL5 and PL9 groups compared to PL1 group indicating that 1% phospholipid incorporation in diet was not sufficient to induce good enterocyte maturation. Diet fatty acid composition was affected by phospholipid incorporation, dietary n − 3 HUFA concentration decreasing with the incorporation of PL. Fatty acid composition in larvae reflected that of corresponding diet. The best results in growth and development obtained in the PL9 group seemed related to the PL entity, independently of its fatty acid composition. The results of this study indicate that pikeperch larvae have a relatively high PL requirement (at least 9.5% of the diet, dry weight).

This work describes the ontogeny of the digestive tract in thick lipped grey mullet (Chelon labrosus) larvae reared until day 36 post-hatching with the semi-extensive technology in mesocosms. Diet was constituted by live preys, rotifers, Artemia and wild zooplankton, then compound diet was added from day 20 (p. h.). Linear growth, weight growth and digestive enzymes specific activities were studied during larval ontogeny. Pancreatic enzymes (trypsin and amylase) and intestinal enzymes (leucinealanine peptidase "Leu-ala", aminopeptidase N "AN" and alkaline phosphatase "AP") were assayed in larvae sampled throughout the rearing trial to evaluate gastrointestinal maturation along the development. The trypsin specific activities were very high during the first two weeks and then declined as observed in marine fish species. A following increase in trypsin specific activity from day 20 was attributed notably to ingestion of particle compound diet. In contrast to the pattern generally described in fish larvae, amylase specific activity showed a continuous increase. This could be attributed to the fact that C. labrosus is an omnivorous species and suggests that the fish might be able to use efficiently diets containing higher levels of starch or other carbohydrates since the end of larval development. Relative expression of intestinal brush border membrane enzymes (AP and AN) and cytosolic enzyme (Leu-ala), showed an abrupt increase of both AP/leu-ala and AN/leu-ala ratios at day 8 (p. h.), indicating that maturation of intestinal tract in C. labrosus larvae is particularly precocious. It is assumed that larvae of C. labrosus might support early co-feeding and weaning strategies, which could reasonably be initiated since mouth opening.

Allometric growth and ontogeny were studied in thick-lipped grey mullet Chelon labrosus reared in mesocosms from 1 to 71 day post hatching (dph). Multivariate allometric analysis of morphometric growth distinguished three distinct developmental stanzas separated by two morphometric metamorphosis lengths (L m1 = 4.46 ± 0.06 mm; L m2 = 28.56 ± 1.04 mm). Body mass growth also showed three distinct episodes separated by two inflections, correlated with morpho-functional changes. First episode concerned pre-flexion larvae and ended around 4.5 mm-L T (14-dph), coinciding with estimated L m1 . It was distinguished by reduced growth, but intense morphogenesis and differentiation processes. Organogenesis and allometric changes indicated that development priorities concerned feeding efficiency, by improving detection ability (sensory system development), ingestion capacity (head growth) and assimilation performance (digestive system differentiation), together with respiration efficiency (gill development). Second episode concerned post-flexion larvae and, ended around 8.6 mm-L T (25-dph). It was distinguished by fast growth of trunk and tail, acquisition of adult axial muscle distribution and completion of gill filament development, improving locomotion and oxygenation performances. It cor-responded to transition towards metamorphosing stage as indicated by later isometric growth, musculature maturation and acquisition of juvenile phenotype. Metamorphosis seemed to end at L m2 , suggesting to avoid zootechnic handling before this size.

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A commercial microencapsulated diet was used as a total or partial replacement of live prey for feeding larvae of winter flounder Pseudopleuronectes americanus (Walbaum), a potential alternative finfish species for coldwater marine aquaculture. Growth performance (morphometric measurements and biochemical composition) and nutritional condition (RNA/DNA ratios) of larvae fed live prey (Brachionus plicatilis Müller), a microencapsulated diet or a mixed diet of live prey and microcapsules were compared. Newly hatched larvae were unable to digest microencapsulated diet; live prey at initial feeding was required for their survival and growth. Larvae offered a mixed diet showed slower growth than larvae fed exclusively with live prey. However, at the onset of stomach differentiation, RNA/DNA ratios (indicators of protein synthesis potential) of the larvae fed both diets became similar. We suggest that, at that stage (size 5.5–6.3 mm), enzymatic activity had developed enough to allow digestion of inert food. As the RNA/DNA ratio is a good indicator of nutritional condition, it appears to be an interesting tool for the assessment of diet adequacy in marine larval feeding technology.