No abstract

The aim of this study was to evaluate the effect of dietary lipid classes (phospholipid vs. neutral lipid) and level of n-3 highly unsaturated fatty acids (HUFAs) on growth, survival and digestive enzymatic activity in Atlantic cod (Gadus morhua) larvae. Larvae were fed enriched rotifers from mouth opening and were weaned to formulated diets during a co-feeding period lasting from 17 days post hatch (dph) to 24 dph. Larvae were fed exclusively compound diets from 24 dph until the end of the experiment. Three isoproteic and isolipidic compound diets with gradually decreasing levels of DHA and EPA in the dietary phospholipid fraction (diet PL3 > PL1 > NL1) and increasing levels of total dietary neutral lipids (PL3 < PL1 < NL1) were used. Larvae fed the PL3 or PL1 had a significant higher dry weight than larvae fed the NL1 diet at the end of the experiment (45 dph). Survival did not differ significantly between treatments. A gut maturation index based on the relation between the amount of the brush border enzyme alkaline phosphatase and the cytosolic enzyme leucine-alanine aminopeptidase showed that the enterocyte maturation on 35 and 45 dph was better in larvae fed the PL3 and PL1 diet than larvae fed the NL1 diet. Dietary composition did not significantly affect the activity of α-amylase, but an age specific decrease in activity was observed. The dietary composition did affect the specific activity of trypsin, although showing variation in pattern between different larval ages at sampling. The activity of neutral lipase showed high variability between dietary treatments, but at the end of the experiment the specific activity of neutral lipase was positively connected to the dietary neutral lipid levels. The results from this study showed that cod larvae use DHA and EPA in the phospholipid fraction more efficiently compared to those in the neutral lipid fraction.

Dietary essential fatty acids may affect larval skeletal formation. The aim of this study was to compare effects on growth and osteological development of dietary docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) being incorporated in the phospholipid (diets PL1 and PL3) or in the neutral lipid (diet NL1) fraction of the larval diet for Atlantic cod (Gadus morhua). The diets were labelled according to the estimated percentage of total n−3 fatty acids contained in the dietary neutral lipid (NL1-1.3% of dietary dry matter) or in the phospholipid fraction (PL1-1.1% and PL3-2.3%). Larvae were weaned to the isoenergetic and isolipidic microdiets from 17 days post hatching (dph). They were co-fed enriched rotifers until 24 dph and received thereafter only the experimental diets until 45 dph (at 12 °C). Dry weight on 45 dph was significantly higher in the PL1-and PL3-larvae (mean 2.74 ± 0.2 mg DW) than in the NL1-larvae (mean 2.17 ± 0.1 mg DW). Larvae fed the PL3-diet had a significantly higher DHA content than larvae from the other treatments. No differences were found in larval content of EPA and arachidonic acid (ARA). Larvae fed both PL-diets showed a significantly faster ossification of the vertebral column compared to larvae fed the NL1-diet, according to both larval size and age. On 45 dph, PL3-larvae also had a significantly higher number of fin rays than the other groups at comparable larval sizes. Deformities (mainly kyphosis and shortened vertebrae) were observed in 11% (all groups) of the larvae on 45 dph, with no significant differences among the groups. Ossification of the vertebral column in the cod larvae was first observed in the neural arches on the anterior part of the spine (21 dph, > 6.9 mm standard length, SL), followed by the vertebrae (25 dph, > 7.9 mm SL), haemal arches (31 dph, ≥ 8.4 mm SL) and parapophysis (35 dph, > 8.7 mm SL). Ossification of all vertebral elements was observed in 45-day-old larvae ≥ 11.4 mm SL. Large variations between larvae in number of ossifying structures between 31 and 35 dph demonstrated that this was the period of most rapid skeletal change (size range 8.2-11.4 mm SL), and that the ossification process was more susceptible to fatty acid lipid source rather than to quantity of dietary fatty acids. We suggest that an optimal dietary content of n−3 HUFA in feed for cod larvae is higher than in the PL1-diet.

The aim of the present study was to compare effects of dietary n-3 highly unsaturated fatty acids (HUFA) being incorporated in the phospholipid (PL) or in the neutral lipid (NL) fraction of the larval feed, on larval growth and histology of digestive organs in Atlantic cod (Gadus morhua L.) larvae. Three isoproteic and isolipidic diets, labelled according to the percentage of n-3 docosahexaenoic acid and eicosapentaenoic acid contained in NL1 or in PL1 and PL3 of the diets, were fed to cod larvae from 17 days post hatching (dph) to 45 dph.In the liver, hepatocytes and their nuclei were smaller in NL1 larvae compared with the PL larvae; the mitochondrial membrane structures were less dense and the amount of lipids observed in the liver was significantly higher in NL1 larvae compared with the PL3 larvae. The liver and gut size was related to larval size, with no differences between the larval groups. The results demonstrated that the essential fatty acids were more beneficial for cod larvae when they were incorporated in the dietary polar PL rather than in the NL, and that the n-3 HUFA requirements in cod larvae is possibly higher than that in the PL1 diet. KEY WORDS

The aim of this study was to compare the nutritional composition and effects of short periods with cultivated copepod nauplii versus rotifers in first‐feeding. Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae were given four different dietary regimes in the earliest start‐feeding period. One group was fed the copepod Acartia tonsa nauplii (Cop), a second fed enriched rotifers (RotMG), a third fed unenriched rotifers (RotChl) and a fourth copepods for the seven first days of feeding and enriched rotifers the rest of the period (Cop7). Cod larvae were fed Artemia sp. between 20 and 40 dph (days posthatching), and ballan wrasse between 36 and 40 dph, with weaning to a formulated diet thereafter. In addition to assessing growth and survival, response to handling stress was measured. This study showed that even short periods of feeding with cultivated copepod nauplii (7 days) had positive long‐term effects on the growth and viability of the fish larvae. At the end of both studies (60 days posthatching), fish larvae fed copepods showed higher survival, better growth and viability than larvae fed rotifers. This underlines the importance of early larval nutrition.