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A study was undertaken to determine the dietary protein level for optimal growth performance and body composition of juvenile Senegalese sole. Five experimental extruded diets were formulated to contain increasing levels of protein [430, 480, 530, 570 and 600 g kg−1 dry matter (DM)] and a constant lipid level, ranging from 100 to 130 g kg−1 DM. Triplicate groups of 35 sole (initial body weight: 11.9 ± 0.5 g) were grown over 84 days in 60-L tanks supplied with recirculated seawater. Fish were fed by means of automatic feeders in eight meals per day. At the start and end of the trial, whole-body samples were withdrawn for proximate composition analysis. At the end of 84 days of experimental feeding, daily weight gain and specific growth rate in fish fed diets P43 and P48 were significantly lower than those found in fish fed higher protein level diets (P53, P57 and P59). Similarly, feed efficiency was also significantly lower in fish fed diet P43 than in fish fed all other dietary treatments. Sole juveniles fed lower protein level diets (P43 and P48) showed a significantly lower protein content than fish fed the higher dietary protein level treatments (P53, P57 and P60). Changes within the tested dietary protein levels did not affect significantly protein productive value or total nitrogen (N) losses in fish. However, daily N gain was significantly higher ( P < 0.05) in fish fed diets P53 and P60 than in fish fed the lowest protein level diet (P43). Data from the present study indicate that diets for juvenile Senegalese sole should include at least 53% crude protein to maintain a good overall growth performance. Based on a second-order polynomial regression model, the daily crude protein requirement for maximum whole-body N gain as estimated here for Senegalese sole juveniles was 6.43 g kg−1 body weight day−1 which corresponds to a value of 1.03 g N intake kg−1 body weight day−1. If the present data are expressed on a dietary crude protein concentration basis, the allowance for maximum protein accretion (N gain) would be met by a diet containing a crude protein level of 600 g kg−1. [ABSTRACT FROM AUTHOR]

A large effort has been dedicated in the past years to the development of nutritional balanced inert diets for marine fish larvae in order to suppress the nutritional deficiencies of live feed. In this study growth performance, Artemia intake, protein digestibility and protein retention were measured for Senegalese sole ( Solea senegalensis Kaup), in order to provide insight into how protein utilization affects growth performance. Three feeding regimes were tested: ST – standard live feed; ArtRL – live feed and 20% Artemia replacement with inert diet (dry matter basis) from mouth opening; ArtRH – live feed and 58% Artemia replacement with inert diet from mouth opening. Artemia intake and protein metabolism were determined at 6, 15 and 21 days after hatching using 14C-labelled Artemia protein and subsequent incubation in metabolic chambers. At the end of the experiment, sole fed exclusively with live feed were significantly larger than sole from Artemia replacement treatments. Protein digestibility decreased during sole ontogeny, and more sharply in ArtRH sole. Concomitantly retention efficiency increased during ontogeny but with a slight delay in ArtRH sole. Senegalese sole larvae growth and protein utilization is depressed when co-fed high levels of inert diet and Artemia, mostly during metamorphosis climax. [ABSTRACT FROM AUTHOR]

The digestion, absorption and post absorptive metabolism of a radiolabelled triacylglycerol (TAG; triolein) and a free fatty acid (FFA; oleic acid), delivered by tube feeding, was studied in herring Clupea harengus larvae, using metabolic chambers and video analysis. In general, a large amount of the delivered lipid was evacuated. Most of the evacuation occurred between 2 and 6 h after tube feeding although a group of larvae responded by rapidly evacuating the lipid (>50% before 2 h). The volume of the tube-fed lipid affected its utilization. A small volume of triolein (9·2 nl, representing c. 6% of gut filling capacity) resulted in a lower proportion of fast evacuating larvae and improved utilization (lower evacuation and higher absorption: body incorporation and catabolism) compared with 50·6 nl ( c. 17% of gut filling capacity). Increases in the volume of tube fed triolein enhanced only marginally label absorption and led to a steep rise in evacuation. At a comparable high volume (50·6 nl), oleic acid, which does not require digestion, was better absorbed and less evacuated than triolein. The video observation of the lipid digestive process revealed a considerable gut contractile activity that appeared effective in processing the tube fed lipid. Also, the gut wall seemed very sensitive to physical pressure. Signs of chemical degradation during lipid digestion were also noted. The metabolic studies, together with video image analysis, suggested that the limiting step for the utilization of high dietary lipid levels may have been the lipid absorption into the enterocytes and transport into the body, rather than lipid digestion. The results support the notion that the rate of lipid digestion and absorption in fishes is slower than that of mammals. [ABSTRACT FROM AUTHOR]

Ontogenetic changes in the capacity of Senegalese sole (Solea senegalensis Kaup, 1858) larvae to digest and metabolise Artemia protein and amino acids (AA) were studied using 12, 22 and 35 days after hatching (DAH) larvae that were fed Artemia metanauplii radiolabelled with a [U-14C] protein hydrolysate. About 82% and 18% of the label was incorporated into the Artemia trichloroacetic acid (TCA) precipitate (mostly protein) and soluble (mainly free AA) fractions, respectively. The digestibility of Artemia was high at all tested ages, with label absorption varying between 77% and 83% at 24 h after feeding (HAF). A rapid digestion, absorption and catabolism of Artemia AA were noted, with most of the absorption into the body occurring during the first 3 HAF. Traces of label were already found in the metabolic-CO2 trap at 1 HAF. Furthermore, label was largely and almost immediately incorporated into the TCA precipitate fraction (mostly protein) of gut and body tissues. Slight differences were noted in diet utilization between larvae at different ages. At 12 DAH larvae had a lower catabolism and evacuation of the label, as well as the highest accumulation in the gut. However, except for the amount of catabolised label, the results were not significantly different from those for 35 DAH larvae. Moreover, no significant differences were found in the amount of label incorporated into the body, although it seemed to be higher in 12 DAH larvae. Taken together, these results reveal a higher absorption and a significantly higher retention of the absorbed label in 12 DAH larvae. In addition, 12 DAH larvae appeared to have a slower absorption of the label, which, in continuously feeding larvae, might result in overall lower food absorption efficiency. Therefore, it seems that young larvae have the ability to compensate for a possible lower digestive capacity with higher body retention of absorbed AA. This study confirms that sole larvae, even young stages, have a high capacity for digesting live preys. [ABSTRACT FROM AUTHOR]

Abstract: In this study, two different dietary protein levels were tested (500 and 600 g/kg) in meagre juveniles of approximately 2 g, to determine whether a higher body protein diet would favour muscle growth. Results showed that meagre survival and growth were not affected by different levels of dietary protein. However, a higher content of protein was observed in the body composition of meagre fed the P60 diet (656 g/kg versus 624 g/kg). When fish were 82 days after hatched (DAH), protein retention efficiency was significantly higher in fish that were fed the P50 diet (37.1% versus 32.5%). Muscle cellularity changed considerably from the beginning to the end of the trial. The contribution of fibre hyperplasia to muscle growth was reduced although still accounted for 30% in 96 DAH meagre. Several differences were found in the frequency of fibres with areas between 1,000 μm2 and 2,200 μm2 between younger and older meagre, but no effect was found associated with dietary protein. This study suggests that neither growth nor muscle cellularity of fast‐growing juvenile meagre is positively affected by an increased dietary protein levels. [ABSTRACT FROM AUTHOR]

Abstract: Formulation of diets according to fish amino acid (AA) qualitative requirements may improve fish growth. Two diets with different AA profiles were tested on 16‐day‐old meagre during 20 days. The first diet had an AA profile closer to meagre larval AA requirements (BAL), whereas the second had a different AA profile (UNBAL). Results showed that larvae fed the diet with higher similarities to the AA profile of meagre carcass had a higher final weight (19.8 ± 0.5 mg versus 13.4 ± 1.8 mg) and lower ammonia excretion after being fed (0.6 ± 0.1 ml/(g DW. larvae. h) and 0.8 ± 0.1 ml/(g DW larvae. h)). A higher mean fibre area was obtained in 36 DAH larvae fed the BAL diet (224.8 ± 33.3 μm2 versus 158.8 ± 34.5 μm2) as well as higher larval weight. When fibre area distribution was analysed, a higher frequency of larger fibres was observed in 36 DAH BAL larvae, suggesting that fibre hypertrophy had a higher importance in this treatment. In conclusion, this study shows that meagre larvae fed a diet with an AA profile closer to their requirements had lower nitrogen losses and higher final weight, as result of higher muscle hypertrophy. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of dietary protein hydrolysates (PH) on larval growth performance, skeleton quality and proteome expression, triplicate groups of white seabream ( Diplodus sargus) larvae were co-fed from first-feeding with live feed and three microencapsulated diets differing in the molecular weight of their PH fraction (Control - inclusion of CPSP-90; H - inclusion of a high amount in 0.5-30 kDa hydrolysates; L - inclusion of a high amount in <0.5 kDa hydrolysates). At 15 days after hatching (DAH), proteome expression changes were assessed in entire larvae by two-dimensional gel electrophoresis and the quality of larval skeleton was analysed at 28 DAH through double staining of cartilage and bone. Dietary PH fractions tested affected growth, the larvae fed diet L being significantly larger than those fed diet H, but it did not affect the incidence of deformed larvae, nor the number of deformities per fish. Two-dimensional analysis of larvae proteome allowed the detection and the comparative quantification of a total of 709 protein spots having a pI between 4 and 7, around half of which had an expression significantly affected by dietary treatment, the main difference being between proteome of Control larvae with those of both groups L and H. From these spots, 52 proteins involved in diverse processes such as cytoskeletal dynamics, energetic, lipoprotein, amino acid (AA), and nucleotide metabolisms, protein chaperoning and degradation, and signal transduction, were identified. This study revealed that the molecular weight of the dietary protein hydrolysate fraction had a minor impact on skeletal deformities in white seabream larvae, but affected growth performance and had a strong impact on larvae whole body proteome. [ABSTRACT FROM AUTHOR]

Temperature is a factor known to have a marked influence on metabolism and consequently on development, inducing ontogenetic plasticity in fish larvae. In this study, three different temperatures (15, 18 and 21°C) were assayed during Solea senegalensis embryonic development prior to hatching. After hatching all larvae were reared at the same temperature (21.0 ± 0.1°C) until 30 days. We observed that lowering the incubation temperature from 21 to 15°C reduced the incidence of skeletal deformities from 80 to 60%. Intermediate incubation temperature (18°C), resulted in larvae that displayed a rate of abnormalities close to that observed at 15°C (64%). A similar typology of deformities was observed in fish from all rearing temperatures, with caudal vertebra being the most affected structures and with a low incidence of cranial and appendicular deformities. The effect of temperature in developmental plasticity will lead to osteological abnormalities mainly affecting the caudal vertebrae at 18°C (30%) and particularly the preural vertebra at 15°C (55%). Our results, clearly demonstrate a significant effect of water temperature during egg incubation on the skeletal development of Senegalese sole, indicating that 18°C is the most appropriated temperature. These findings highlight the importance of tightly controlling temperature regimes during the early development of S. senegalensis, and the need for optimizing rearing protocols in order to avoid skeletal disorders or impaired growth. [ABSTRACT FROM AUTHOR]

Fish larvae present high amino acid requirements due to their high growth rate. Maximizing this growth rate depends on providing a balanced amino acid diet which can fulfil larval amino acid nutritional needs. In this study, two experimental microencapsulated casein diets were tested: one presenting a balanced amino acid profile and another presenting an unbalanced amino acid profile. A control diet, live feed based, was also tested. Trials were performed with larvae from 1 to 25 days after hatching (DAH). Microencapsulated diets were introduced at 8 DAH in co-feeding with live feed and at 15 DAH larvae were fed the microencapsulated diets alone. Results showed a higher survival for the control group (8.6 ± 1.3% versus 4.2 ± 0.6% and 3.2 ± 1.8%) although dry weight and growth were similar in all treatments. The proportion of deformed larvae as well as the ammonia excretion was lower in the group fed a balanced diet than in the unbalanced or control groups (38.3% deformed larvae in control, 30% in larvae fed unbalanced diet and 20% on balanced diet group). Furthermore, larvae fed the microencapsulated diets presented higher docosahexaenoic acid and arachidonic acid levels. This study demonstrates that dietary amino acid profile may play an important role in larval quality. It also shows that balanced microencapsulated diets may improve some of the performance criteria, such as skeletal deformities, compared to live feeds. [ABSTRACT FROM AUTHOR]