DIGESTIVE AND ASSIMILATION CAPACITY OF MARINE FISH LARVAE WITH RESPECT TO DIETARY LIPID/PROTEIN RATIOS AND LIPID QUALITY

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Digestive physiology and food intake in marine fish larvae with respect to dietary neutral lipids

Publication . Morais, Sofia Jacinto

A growth depressing effect of high dietary neutral lipid levels in marine fish larvae has been reported. This may be the result of a decrease in the efficiency or activity of digestive enzymes, a reduction in absorption efficiency and/or a decrease in food intake. In this thesis, work was carried out on commercially valuable species (Atlantic herring, Senegalese sole, European seabass and gilthead seabream), to investigate the effects of neutral lipid level and source (fatty acid composition) on some of these key factors influencing larval growth. The results seem to collectively indicate that lipid transport from the enterocytes into the body may be more problematic in larval stages dealing with high neutral lipid diets than lipid digestion, although both factors are likely to intervene. Food intake did not appear to be strictly regulated by total lipid content of the diet and lipid source may have an important role in controlling ingestion. Therefore, the neutral lipid level in diets for marine fish larvae has a significant impact in several factors influencing growth but clearly it cannot be dissociated of its fatty acid composition, which appears to play a central role on the nutritional and physiological effects of dietary lipid, at the ingestion, digestion and absorption levels.

2005Doctoral thesis

Open access

A new method for the study of essential fatty acid requirements in fish larvae

Publication . Morais, Sofia; Conceicao, Luis

This study describes a methodology with potential application in the estimation of essential fatty acid (EFA) requirements of fish larvae. Senegalese sole (Solea senegalensis) larvae were fed, from 16 days after hatching (DAH), on Artemia enriched with different oils, inducing graded dietary concentrations of DHA: (1) soyabean oil, containing no measurable amounts of DHA (NDHA); (2) fish oil, inducing a medium DHA level (MDHA, 3 g DHA/100 g fatty acids); and (3) a mixture of Easy DHA Selco and Microfeed, resulting in high DHA content (HDHA, 8 g/100 g). At 28 DAH a metabolic trial was conducted where larvae were tube fed [1-(14) C]DHA, in order to determine its absorption, retention in the gut and body tissues, as well as its oxidation. At 23 DAH the HDHA treatment induced a significantly higher larval growth, while at 32 DAH significant differences were only found between the NDHA and HDHA treatments. The absorption of tube-fed [1-(14) C]DHA was extremely high (94-95%) and independent of feeding regime. However, in larvae fed NDHA Artemia, a significantly higher amount of label was retained in the gut compartment and a concurrently lower retention was measured in the body. A significantly higher proportion of the absorbed DHA label was oxidized in larvae fed HDHA, compared to NDHA. Based on these results, we suggest that increasing dietary supply of DHA above the larval requirement level results in its increased oxidation for energy purposes and we propose potential applications of the tube feeding methodology using radiolabelled EFA in conjunction with dose-response studies.

2009-05Journal article

Open access