Nutritional physiology during development of Senegalese sole (Solea senegalensis)

CCMAR-Centre of Marine Sciences, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
Aquaculture (Impact Factor: 1.83). 08/2007; 268:64-81. DOI: 10.1016/j.aquaculture.2007.04.030

ABSTRACT The Senegalese sole, a species with a complex metamorphosis, difficulties in weaning and with occasional problems of malpigmentation and skeletal deformities, is a good model species to study larval nutritional physiology. In addition, the early metamorphosis and acquisition of a peculiar non-proactive bottom-feeding behaviour make early weaning an important issue in sole hatcheries. The present work reviews recent findings in different aspects of nutritional physiology during the development of Senegalese sole, in an attempt to optimize the composition of sole diets and to understand what are the limiting factors for weaning sole. Both digestive enzymes activity and tracer studies using 14C-Artemia show that sole larvae, even at young stages, have a high capacity for digesting live preys. This is reflected in a high growth potential and low mortality rates for this species during the larval stage compared to other marine fish species. Based on the observation of the digestive enzymes profile, early introduction of inert microdiets in co-feeding with Artemia does not seem to affect intestinal function. However, when co-feeding is not provided, intestinal activity may be depressed. Furthermore, early introduction of microdiets in co-feeding with Artemia may have a positive effect on survival rates, but at the expense of lower growth rates and higher size dispersal. This may reflect variation in the adaptation capacity of individual larvae to inert diets. High dietary neutral lipid (soybean oil) content results in reduced growth and accumulation of lipid droplets in the enterocytes and affects the capacity of Senegalese sole larvae to absorb and metabolise dietary fatty acids (FA) and amino acids (AA). Through tube feeding of different 14C-lipids and free FA it has been shown that FA absorption efficiency increases with unsaturation and that sole larvae spare DHA from catabolism. In addition, it was demonstrated that absorption efficiency varies according to molecular form, being highest for free FA, lowest for triacylglycerols and intermediate for phospholipids. Live preys commonly used in larviculture do not seem to have a balanced AA profile for sole larvae. Furthermore, the ideal dietary AA composition probably changes during development. Rotifers and Artemia metanauplii are apparently deficient in one or more of the following AA depending on the larval development stage: histidine, sulphur AA, lysine, aromatic AA, threonine and arginine. It has also been demonstrated that balancing the dietary AA profile with dipeptides in Artemia-fed larvae increases AA retention and reduces AA catabolism. When supplementing larval diets with limiting AA it should also be considered that sole larvae have different absorption, and retention efficiencies for individual AA, and that they have the capacity to spare indispensable AA. In addition, the absorption of free AA is faster and more efficient than that of complex proteins. Improvements in biochemical composition of inert microdiets for sole are likely to contribute to the reproducible weaning success of Senegalese sole.

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    ABSTRACT: The aim of this work was to assess the effects of a dietary supplement of vitamin C (as ascorbyl palmitate, AP) delivered through new and optimized alginate microcapsules (MA) on larval performance, antioxidant status and gene expression profiles. For this purpose, three MA (referred to as MA-1, MA-2 and MA-3) with increasing AP content ranging from 1,700 to 5,700 µg AP g−1 DW were assayed. Sole larvae were fed the three MA from first feeding to 7 days post-hatch (dph) and later replaced by Artemia from 7 to 28 dph. The experimental groups were performed in triplicate using a recirculation system. The efficiency of AP inclusion into MA was 55 %. At 7 dph, larval ascorbic acid (AA) content was proportional to the AP concentration included in MA (p<0.05). Larval growth until 7 dph was low but significantly higher in larvae fed MA-2 and MA-3. After Artemia supplying, a compensatory growth was detected in the three experimental groups whereas a faster metamorphic process and a higher weight at 28 dph in larvae fed MA with a higher AP content (MA-2 and MA-3) was observed (p<0.05). Moreover, Artemia feeding substantially increased the larval AA content during development peaking at 18 dph and decreasing at the end of metamorphosis with significantly lower AA levels in larvae fed MA-3. This reduction coincided with a higher total antioxidant capacity and lipid peroxidation whereas no differences in catalase or total glutathione peroxidase were detected. Expression data revealed that MA diets significantly modified the transcript levels of 16 genes involved in antioxidant defence (gpx1), tissue structure (col1a1 col1a2 and col1a3), stress (hsc70-1, hsc70-2, hsc70-3, gr1, gr2, pomcb), glycolytic pathway (gapdh1 and pkm), osmoregulation (cftr, nkcc2 and nkcc1) and pigmentation (mc1r). All these data reveal novel new insights about role of vitamin C during early stages of S. senegalensis to modulate growth, stress and antioxidative status in later developmental stages
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    ABSTRACT: The aim of this study was to examine patterns of food intake and production of the main digestive enzymes of Senegalese sole larvae under a fixed 12 h light:12 h dark cycle. Daily gut content, soluble protein content and digestive enzyme activities were studied at different times of day in pelagic sole larvae (onset of feeding and 6 days post-hatch; dph) and in benthonic sole post-larvae (20 and 30 dph). The larvae displayed temporal changes in food intake throughout development. Pre-metamorphic larvae ceased feeding after lights were turned off. In contrast, post-metamorphic larvae continued to feed during the day, with a higher food intake occurring during dark phase. It was demonstrated that larval digestive enzymes, mainly lipases, were active before mouth opening. Tryptic activity varied with food intake at pre-metamorphic larvae, whereas its activity levels were kept along the day in post-metamorphic larvae.
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    ABSTRACT: The aim of this work was to evaluate the genomic responses of premetamorphic sole larvae (9 days post-hatching, dph) fed diets with different lipid and triacylglycerol (TAG) content. For this purpose, two diets with high (rotifers enriched with a fish oil-based emulsion; referred to as HTAG) and low (rotifers enriched with a krill oil-based emulsion; LTAG) levels of total lipids and TAG were evaluated. Lipid class and fatty acid (FA) profiles, histological characterization of intestine, liver and pancreas and expression patterns using RNA-seq were determined. Discriminant analysis results showed that larvae could be clearly differentiated on the basis of their FA profile as a function of the diet supplied until 9 dph although no difference in growth was observed. RNA-seq analysis showed that larvae fed HTAG activated coordinately the transcription of apolipoproteins (apob, apoa4, apoc2, apoe, and apobec2) and other related transcripts involved in chylomicron formation, likely to facilitate proper lipid absorption and delivery. In contrast, larvae fed LTAG showed higher mRNA levels of several pancreatic enzymes (try1a, try2, cela1, cela3, cela4, chym1, chym2, amy2a and pnlip) and appetite modulators (agrp1) and some intra- and extracellular lipases. Moreover, KEGG analysis also showed that several transcripts related to lipid metabolism and glycolysis were differentially expressed with a higher abundance in larvae fed LTAG diet. All these data suggest that early larvae were able to establish compensatory mechanisms for energy homeostasis regulating key molecules for FA and TAG biosynthesis, FA uptake and intracellular management of TAG and FA to warrant optimal growth rates.
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