Evaluation of corn gluten meal as a protein source in diets for gilthead sea bream (Sparus aurata L.) juveniles

A 12‐week growth trial was conducted to evaluate corn gluten meal as an alternative protein source to fish meal in diets for gilthead sea bream juveniles. The experimental diets were formulated to be isonitrogenous and isoenergetic and to have 20%, 40%, 60% and 80% of fish meal protein, the only protein source in the control diet, replaced by corn gluten meal. At the end of the growth trial only the group fed the diet with 80% corn gluten protein exhibited significantly reduced growth and feed efficiency compared with the fish meal‐based diet. This was most likely due to a dietary amino acid deficiency in that diet. A trend was noticed for feed efficiency to improve with the replacement of fish meal protein in the diets up to 60%. There were no significant differences among groups in protein and energy retention (as percentage of intake). At the end of the trial whole body water content of the experimental groups was significantly lower and the lipid content of groups including 60% and 80% corn gluten protein was significantly higher than that in the control. No other differences were observed in whole body composition among groups. Apparent digestibility coefficients (ADC) of the diets were evaluated in a separate trial. The ADC of dry matter of the experimental diets was significantly higher than in the control diet; there were no significant differences among diets in the ADC of energy and protein, except for the ADC of protein of diet with 80% corn gluten protein, which was significantly lower than the control. The results of this study indicate that corn gluten meal can replace up to 60% fish meal protein in diets for gilthead sea bream juveniles with no negative effects on fish performance.     

Phosphorus requirement of European sea bass (Dicentrarchus labrax L.) juveniles

A growth trial was conducted to estimate the phosphorus requirement of European sea bass juveniles. Six experimental isonitrogenous and isoenergetic semi‐purified diets (casein based) were formulated to contain 0.48%, 0.65%, 0.77%, 0.86%, 1.05% and 1.25% phosphorus (diets D1, D2, D3, D4, D5 and D6 respectively). Dicalcium phosphate was used as dietary phosphorus source. Twelve groups of 25 fish of 10 g initial body weight were allocated to 55‐L tanks in a thermoregulated water recirculating system. Each experimental diet was assigned to duplicate groups of these fish. The trial lasted for 10 weeks and fish were fed two times a day, 6 days a week, to apparent visual satiation. At the end of the trial, final weight of fish fed diet D1 was significantly lower than that of the other groups, except of fish fed diet D4. Mortality of fish fed diet D1 was significantly higher than that of fish fed the other diets, except for diet D6. Feed efficiency and protein efficiency ratios were significantly lower with diet D1 than with the other diets. Nitrogen retention (% nitrogen intake) of fish fed diet D1 was significantly lower than in the other groups, except that of fish fed diet D4. Energy retention (% energy intake) was not significantly different among groups. At the end of the trial there were no differences in whole body composition among groups. Whole body phosphorus content averaged 0.72% (on a fresh weight basis) and was not significantly affected by dietary phosphorus content. Phosphorus retention averaged 6.1 g kg^?1 weight gain and was not significantly different among groups. Phosphorus retention (% phosphorus intake) was significantly higher in fish fed diets D2 and D3 than in fish fed higher dietary phosphorus levels. Expressed per unit body weight per day, phosphorus retention was not significantly different among groups fed diets D2 to D6, while phosphorus losses linearly increased with dietary phosphorus intake. Results of this trial indicate that the phosphorus requirement of sea bass juveniles was satisfied with a diet containing 0.65% of phosphorus.     

Evaluation of micronized lupin seed meal as an alternative protein source in diets for gilthead sea bream Sparus aurata L. juveniles

A 12‐week growth trial was performed to evaluate the effect of lupin seed meal as a protein source in diets for gilthead sea bream (Sparus aurata) juveniles. Six experimental diets were formulated to be isonitrogenous and isoenergetic and to contain 10%, 20% and 30% of raw lupin (Lupinus angustifolius) seed meal protein or 20% and 30% lupin (L. angustifolius) seed meal processed by infrared radiation (micronized) in place of fish meal protein, the only protein source of the control diet. Fish accepted all diets well and no significant differences in feed utilization among groups were noticed during the trial. Final weight of fish fed the experimental diets was identical or higher than the control group. Final weight of fish fed diets including 20% micronized lupin protein was even significantly higher than that of fish fed the fish meal‐based control diet. Moreover, at the same dietary lupin seed meal protein inclusion levels, final weight of fish fed diets including micronized lupin was significantly higher than with raw lupin. A trend was also noticed for a decrease of final weight with the increase in lupin seed meal in the diets. At the end of the trial no significant differences in proximate whole‐body composition, hepatosomatic and visceral indices were observed among groups. It is concluded that lupin seed meal can replace up to 30% fish meal protein in diets for gilthead sea bream juveniles with no negative effects on growth performance. Furthermore, micronization of lupin seeds improves its dietary value for gilthead sea bream juveniles. At the same dietary lupin inclusion levels, diets including micronized lupin seeds promote significantly higher growth rates than raw lupin seeds.     

Preliminary evaluation of pea seed meal in diets for gilthead sea bream (Sparus aurata) juveniles

Juvenile gilthead sea bream with a mean initial body weight of 5 g were fed for 12 weeks with experimental diets containing 10% and 20% fishmeal protein (sole protein source in the control diet) replaced by processed pea seed meals. The processed pea seed meals were dehulled, defibred, extruded and microground pea seed meal (PSM1) or whole pea treated by infrared radiation and ground (PSM2). Apparent digestibility coefficients of the experimental diets were determined in a separate trial. At the end of the growth trial there were no significant differences in growth performance, feed utilization or whole-body composition among experimental groups. There were no differences in apparent protein digestibility among experimental groups (except for fish fed PSM1 at the lowest inclusion level). Both dry matter and energy digestibility of the diets, including PSM2 and with the highest inclusion level of PSM1, were significantly lower than those of the control diet. The results of this study suggest that pea seed meal may replace up to 20% fishmeal protein in diets for gilthead sea bream juveniles without affecting fish performance. Further studies should focus on technological treatments to increase utilization of pea seed meal carbohydrate, as both apparent dry matter and energy digestibility were affected by dietary inclusion level and by pea seed meal processing method.     

Effect of diets containing a purified soybean trypsin inhibitor on growth performance,digestive proteases and intestinal histology in juvenile sea bream (Sparus aurata L.)

Juvenile sea bream were fed on diets containing 0.0, 2.0 or 4.0 g kg^?1 of a soybean trypsin inhibitor (SBTI) for 30 days. The growth performance, total protease activity and intestinal histology were studied after 0, 15 and 30 days of dietary treatment. No significant differences were found in the weight gain, specific growth rate (SGR) and feed conversion rate in fish fed on inhibitor‐supplemented diets when compared with those fed on an inhibitor‐free diet. Only the SGR at day 15 decreased significantly with protease inhibitor inclusion, although this effect was not observed at day 30. In relation to proteolytic activity at day 15, the total protease activity in the distal intestine decreased in fish fed on inhibitor‐supplemented diets. Zymograms of these extracts showed that the SBTI reduced the intensity of some proteolytic fractions in the distal intestine. A noticeable reduction in the protease activity of the intestinal content in fish fed on the highest level of soybean inhibitor (4.0 g kg^?1) was also observed. However, at day 30, the inhibition effect on these active bands was not detected, and the total protease activity was similar to that in fish fed on an inhibitor‐free diet. Histological examination revealed no perceptible differences in the intestinal structure between any of the diet groups. In addition, all fish were maintained under experimentation for 10 more days and fed on an inhibitor‐free diet to determine whether the possible effects caused by the protease inhibitor could be reverted. The administration of SBTI‐supplemented diets did not affect sea bream growth performance or intestine histology after 30 days, and only a decrease in the total alkaline protease activity was found at day 15.     

Effects of dietary mannan oligosaccharides in early weaning diets on growth,survival, fatty acid composition and gut morphology of gilthead sea bream (Sparus aurata,L.) larvae

Early weaning of marine fish larvae with dry diets delays gut maturation and reduces growth rates. In juvenile and adult forms of several marine fish species, inclusion of dietary mannan oligosaccharides (MOS) improves gut integrity and functionality, but the effects of MOS inclusion in gilthead sea bream (Sparus aurata, L.) larval diets have not been addressed yet. Thus, this study assesses the effects of dietary MOS inclusion on survival, growth performance, gut morphology, feed acceptance and quality of gilthead sea bream larvae. For that purpose, 16 days post‐hatched gilthead sea bream larvae were fed four graded levels of MOS (Biomos^®, Alltech, Nicholasville, KY, USA) in weaning diets as follows: 0 g kg^?1 MOS, 0.5 g kg^?1 MOS, 1.5 g kg^?1 MOS and 2 g kg^?1MOS. Dietary MOS did not affect feed acceptance in gilthead sea bream larvae (P > 0.05). MOS supplementation was correlated in a dose‐dependent way with higher larval survival (P = 0.026). After 15 days of feeding, dietary MOS increased whole larvae (P < 0.01) arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid. Gilthead sea bream larvae fed 2 g kg^?1 MOS presented higher gut occupation with goblet cells after feeding compared with larvae fed the other dietary treatments. Overall, the results suggest that inclusion of MOS in early weaning diets for gilthead sea bream improves essential fatty acid utilization and may promote growth and final survival.     

Comparison of the swimming performance of farmed and wild gilthead sea bream, Sparus aurata

Farmed gilthead sea bream, Sparus aurata, frequently escape from the sea cages and interact with wild populations. The impact of these interactions on the wild populations will depend, in part, on differences in performance of the bream. This study compared the swimming performance of the wild and farmed fish in a current channel. The absolute critical swimming speed (U_crit) increased with increasing size while the relative U_crit decreased. Even at the same length there were noticeable performance differences between the individuals. The wild sea bream have significantly higher (P<0.05) absolute U_crit performance (0.86±0.01 m s⁻¹) than the farmed fish (0.79±0.01 m s⁻¹) and significantly higher (P<0.05) relative U_crit performance (4.52±0.05 BL s⁻¹) than the farmed fish (4.21±0.05 BL s⁻¹). The present study suggests that cultured sea bream may not have the ability to compete with wild sea bream in native seawaters.     

Biochemical differences in lateral muscle of wild and farmed gilthead sea bream (series Sparus aurata L.)

Red and white muscle from specimens of wild and farmed gilthead sea bream (Sparus aurata) were analyzed for histochemical ATPase activity, total protein content, fatty acids, trace element concentrations and myosin isoforms. The fibre type composition of muscle samples was confirmed histochemically by the ATPase reaction, which did not show any differences between the two groups of animals. Myosin ATPase activities, myosin and protein yields were significantly higher in white muscle than in the red muscle and for the red muscle the latter two parameters were higher in wild fish. Fatty acid profiles revealed differences between the two groups of animals, probably because of the fatty acid composition of the diets. Zinc, copper and iron concentrations were higher in red muscle than in white muscle; muscles from wild fish were significantly richer in trace elements. No separation of fast and slow heavy chains of myosin could be obtained on SDS-gel electrophoresis, but two dimensional electrophoresis revealed the presence of three light chains in white muscle (LC1F, LC2F, LC3F), and two main types in red muscle (LC1S, LC2S). Small, variable percentages of LC3F were found in the red muscle samples, especially in the wild fish. It is concluded that the different environmental conditions, experienced by wild and farmed fish, have significantly influenced the biochemical composition of their lateral muscle.     

Recent advances in European sea bass and gilthead sea bream nutrition

European sea bass (Dicentrarchus labrax) and gilthead sea bream(Sparus aurata) are amongst the most important finfish speciescultured in the Mediterranean region. Production of these species isnowadays a well-controlled process, but knowledge of their nutritionalrequirements is still very limited. Nevertheless, a considerable amountof data has been accumulated in recent years, and the purpose of thispaper is to review the recent advances on the nutritional requirementsof sea bass and sea bream. The optimum protein to energy ratio of thediets of sea bass and sea bream seem to be higher than for salmonids,and there is some evidence that high dietary lipid levels have nobeneficial effects on fish performances. Although the essential aminoacid requirements were estimated by the ideal protein method, data basedon the dose-response method is only available for a few amino acids.Essential fatty acid requirements were estimated for sea bream juvenilesbut data is lacking for sea bass. Vitamin and mineral requirements ofthese species are practically unknown. Although the importance ofbroodstock nutrition on gonadal development, spawning and egg quality isrecognized, few studies were done to elucidate these aspects. The recentdevelopment of microparticulate diets for larvae will contribute to theaccurate evaluation of their nutritional requirements.     

Nutrient digestibility profile of premium (category III grade) animal protein by-products for temperate marine fish species (European sea bass, gilthead sea bream and turbot)

Three trials, with classical experimental designs for in vivo digestibility studies, were conducted to determine the apparent digestibility coefficient (ADC) of protein (ADCp), lipid (ADCl), energy (ADCe) and amino acids (AA) in selected animal by-products fed to European sea bass, Dicentrarchus labrax (Trial 1), gilthead sea bream, Sparus aurata (Trial 2), and turbot, Psetta maxima (Trial 3). In each trial, five experimental diets [including a reference diet (RD)] where fish meal (FM) was used as the sole protein source were fed ad libitum to the fish for a period of 4 weeks. Test diets were based on the FM RD and obtained by replacing 30% of the RD with a category III designated European animal by-products (fit for human consumption), namely: steam hydrolysed feather meal (HFM), enzyme-treated feather meal (EFM), poultry meat meal (PMM) and spray-dried haemoglobin meal (SDHM). Faecal material was collected using the 'Guelph system', and nutrient and energy digestibility coefficients were related to the measurement of chromic oxide (Cr₂O₃) incorporated into the diet at a rate of 0.5%. Without any exception, FM diets yielded the best digestibility values for all macro-nutrients and by all fish. Among the test ingredients, ADCp was consistently higher for PMM and SDHM in the three species (85.5%, 91.1% in sea bass; 79.2%, 82.8% in sea bream; and 78.4%, 74.8% in turbot). Conversely, ADCp of HFM and EFM were less efficiently digested (67.2%, 68.2% in sea bass; 21.5%, 21.7% in sea bream; and 46.6%, 36.0% in turbot). However, the novel processing method applied to feather meal did not considerably influence the digestibility of most of the nutrients in this feedstuff. The current investigation yielded valuable numerical ADC for EAA considered to be of prime importance in generating balanced diet formulations.     

Compensatory growth response of European sea bass (Dicentrarchus labrax L.) under cycled starvation and restricted feeding rate

The compensatory growth response of the European sea bass (Dicentrarchus labrax) that faced cycling starvation and restricted ration was assessed. Juveniles (10.5 g) were stocked into 15 tanks at a density of 25 fish per tank. Five different feeding regimes were tested on triplicate groups of fish: C_Satiation: control fed for 60 days without deprivation, C_Restricted: 25% restricted feeding, S‐R: 1 day starvation then 4 days C_Restricted feeding, R‐F: 1 day C_Restricted feeding then 4 days C_Satiation feeding, and, finally, S‐F: 1 day starvation then 4 days C_Satiation feeding. The specific growth rate of fish in the C_Satiation (2.5 ± 0.06% day^?1), S‐F (2.5 ± 0.11% day^?1) and R‐F (2.4 ± 0.18% day^?1) were significantly higher than that of C_Restricted (2.2 ± 0.05% day^?1) or S‐R (2.0 ± 0.01% day^?1). Fish in S‐F group were able to achieve catching up with the C_Satiation. There was no significant difference in feed conversion rates but R‐F and S‐F consumed approximately 34% more feed than C_Satiation following the first re‐feeding day. Although, the highest lipid content was observed in C_Satiation (14.4%), S‐R (33.3% dry matter) had the highest water content compared with the C_Satiation and C_Restricted (37.8% and 36.9% dry matter respectively). In conclusion, it may be concluded that sea bass has rapid response to cycling starvation/re‐feeding and that a 25% restricted feeding ratio is insufficient to invoke a compensatory growth response in sea bass.     

Effects of dietary mannan oligosaccharides on growth,body composition and intestine of the sea bass (Dicentrarchus labrax L.)

The effect of Bio‐Mos incorporated into feed formulation on the growth, feed utilization, body composition and histological response of sea bass (Dicentrarchus labrax) was investigated. Final fish weight, feed conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), protein productive value (PPV) and energy utilization (EU) of sea bass feed Bio‐Mos supplemented diet and the control diet were determined at the end of experiment. Data present mean ± SD from triplicate determination (n = 3) for a 75‐day feeding trial. Different concentrations (0.5, 1.0, 2.0. 3.0 and 4.0 g kg diet^?1) of Bio‐Mos supplementation and a control without Bio‐Mos incorporation were fed to the fish, feed in the form of dry diets. Average final weight was significantly higher at 1.0 g kg diet^?1 of Bio‐Mos and lowest in control fish group; SGR significantly higher at the 1.0 g kg diet^?1 of Bio‐Mos. In addition,, PER, PPV and EU showed the same trend. The chemical body composition, crude protein, dry matter, crude fat and ash were significant (P ≤ 0.01) compared to control groups. We concluded that 1.0 g kg diet^?1 of Bio‐Mos improved the growth, feed efficiency, histology intestine and survival of sea bass.     

Effect of broodstock diets on lipid classes and their fatty acid composition in eggs of gilthead sea bream (Sparus aurata L.)

Total lipid content, total lipid fatty acids, lipid classes and their fatty acid compositions were studied in eggs of gilthead sea bream from two different broodstocks. The two broodstock diets used had the same total lipid content, but differed with respect to their fatty acid levels. The lipid class composition of eggs from different origins was not significantly different. The predominant polar lipids were phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, and the main neutral lipid classes were cholesterol esters and triacylglycerols. The fatty acid composition of total lipids and main lipid classes in the two groups of eggs showed marked differences, reflecting the influence of fatty acid levels in the broodstock diets.     

Intestinal bacterial flora of Mediterranean gilthead sea bream (Sparus aurata Linnaeus) as a novel source of natural surface active compounds

Microbial communities play different functions in the digestive tract of fish and represent a source of bioactive compounds. This study was aimed to detect the presence of biosurfactant (BS)‐producing bacteria in the intestine of gilthead sea bream (Sparus aurata L.) to select strains candidate for biotechnological applications in aquaculture. A total of 100 bacterial strains were isolated from the guts of three groups of fish and analysed by different qualitative screening tests and the tensiometric analysis. BSs were extracted, characterized by thin‐layer chromatography (TLC) and their antibacterial activity against bacterial pathogens of interest in aquaculture was determined. A total of 17 out of 100 strains, affiliated to the genera Pseudomonas (11 isolates), Acinetobacter (1 isolate), Sphingomonas (4 isolates) and Aeromonas (1 isolate), displayed a stable emulsion production with the E₂₄ index from 0% to 44%, a surface tension reduction from 8.3 to 30 mN/m and 11 of them exhibited antibacterial activity against fish pathogens. The TLC analysis indicated that the intestinal BSs consisted of compounds ascribed to the class of glycolipids–rhamnolipids. This is the first study reporting on the isolation and selection of BS‐producing bacteria from fish gut, a natural novel source of surface active compounds with potential biotechnological applications in aquaculture.     

Validation of processed animal proteins (mono‐PAPS) in experimental diets for juvenile gilthead sea bream (Sparus aurata L.) as primary fish meal replacers within a European perspective

Experimental diets were formulated to evaluate a “pure” poultry meat meal (PMM) source in diets formulated for juvenile gilthead sea bream (Sparus aurata L.). The digestible protein contribution of fish meal in a control diet was substituted by 25%, 50% and 75% of a processed poultry meat meal (PMM) on a digestible crude protein (DCP) basis and by 5% and 10% for an enzyme‐treated feather meal (EFM) and also a spray‐dried haemaglobin meal (SDHM), respectively. In a consecutive trial, diets were designed to assess the value of a “pure” (defatted) poultry protein substituting the fish meal (FM) protein content. Experimental diets included: a control diet, two test diets where 75% of FM was replaced by a full‐fat PMM (PMM75) or a defatted grade of PMM (dPMM75) and two test diets where 50% of FM was substituted for defatted PMM (dPMM50) or a 50:50 blend of soya bean meal and defatted PMM (SBM/dPMM) to produce a composite product. This soya bean/dPMM blend was tested to enhance the nutritional value of this key plant ingredient commonly employed in sea bream diets that can be deficient in specific amino acids and minerals. In the first trial, gilthead sea bream grew effectively on diets containing up to the 75% replacement of FM attaining a mean weight of 63.6 g compared to 67.8 g for the FM control fed group. For the consecutive trial, the fishmeal‐based control diet yielded the highest SGR followed by dPMM50 and SBM/dPMM blend inclusion but was not significant. Carcass FA profiles of gilthead sea bream conformed to the expected changes in relation to the dietary FA patterns, with the 18:1n‐9 representative of the poultry lipid signature becoming more apparent with PMM inclusion. The ratio of n‐3/n‐6 fatty acids was greatly affected in sea bream fed the full‐fat PMM at 75% inclusion due to fish oil exclusion. Defatted dPMM, however, allowed more of the fish oil to be used in the diet and reducing this latter effect in sea bream carcass, hence restoring the higher total omega‐3 HUFA fatty acids namely EPA and DHA and n‐3/n‐6 ratio. It is concluded that poultry meat meal can be modestly incorporated into formulated diets for sea bream and can be used in conjunction with soya bean meal without any fundamental changes in performance and feed efficiency.