Diets For Sea Bass Research Articles

Effects on mortality and stress response in European sea bass, Dicentrarchus labrax (L.), fed mannan oligosaccharides (MOS) after Vibrio anguillarum exposure

The effects of dietary mannan oligosaccharides (MOS; 4 g kg(-1) ; Bio-Mos, Alltech Inc, USA) in diets for European sea bass, Dicentrarchus labrax (L.), juveniles in relation to disease and stress resistance, combining intestinal infection with Vibrio anguillarum and stress challenge by confinement, were assessed in this study. After 8 weeks of MOS supplementation, fish were exposed to a pathogen challenge test against V.anguillarum by direct gut inoculation combined with a confinement stressor panel. Cumulative mortality of fish fed MOS caused by anally inoculated V.anguillarum decreased from 66% to 12.5% and from 54.1% to 25% in infected and infected + stressed fish, respectively, compared to fish fed control diet. Results for European sea bass revealed a positive effect of MOS dietary inclusion on disease resistance, in terms of cumulative mortality, against gut inoculated V.anguillarum, as well as reduced effects of stress on microbiota diversity. Both of these findings, together with the enhanced innate immune response and the higher gut mucus production and density of eosinophil granulocytes in gut mucosa obtained in previous studies after MOS supplementation (Torrecillas etal. 2007, 2011a,b) suggest that general reinforcement of the innate immune system, and particularly of the intestinal barrier efficiency, is the main defence mechanism of European sea bass fed MOS against pathogenic microorganisms.

Replacement of Menhaden Fish Meal Protein by Solvent‐Extracted Soybean Meal Protein in the Diet of Juvenile Black Sea Bass Supplemented with or without Squid Meal, Krill Meal, Methionine, and Lysine

AbstractThree experiments were conducted to determine the extent to which menhaden fish meal protein (FMP) can be replaced by solvent‐extracted soybean meal protein (SBP) in the diet of juvenile black sea bass Centropristis striata. Diets were formulated replacing FMP by SBP at 0, 10, 20, 30, 40, 50, and 60% (experiment 1) and 0, 60, 70, 80, 90, and 100% (experiment 2), with supplementation with squid meal, krill meal, and attractants in both experiments. Experiment 3 was designed to replace FMP by SBP at 40, 50, 60, 70, and 80% without supplemental squid and krill meal and at 60% and 70% with supplemental methionine and lysine. Diets were fed twice daily to triplicate groups of fish (N = 15 per group) in 75‐L tanks containing recirculating seawater. Fish were fed for 6, 10, and 8 weeks in experiments 1, 2, and 3, respectively. No significant differences in body weight gain, feed efficiency, and survival were observed among treatments in experiment 1. In experiment 2, no significant differences in percent weight gain were observed among fish fed diets replacing FMP at 0, 60, and 70%. In experiment 3, body weight gain was not significantly different for fish fed supplemental methionine and lysine in 70% SBP diets compared with fish fed 0% SBP diets. No significant differences were observed in whole‐body n‐3 polyunsaturated fatty acids among treatments in experiment 2. Broken‐line regression of the specific growth rate data suggested that the maximum level of FMP replacement with SBP in black sea bass diets was 67.6–68.4% with 75 g/kg squid meal and 50 g/kg krill meal in the diet and 57.2–58.0% without squid and krill meal supplementation.

Level of L-ascorbyl-2-monophosphate-Mg as a Vitamin C Source in Practical Diets for the Asian sea bass, Lates calcarifer

The stable vitamin C derivative, L-ascorbyl-2-monophosphate-Mg (AMP), was used as a supplement in practical diets for Asian sea bass, Lates calcarifer. Optimum growth, liver ascorbic acid (AA) saturation, and wound healing were determined. Sea bass (78.9±0.4 g) were fed a maintenance diet without vitamin C supplement for 25 days, then distributed into fifteen 1500-l oval fiberglass tanks at 30 fish each and fed one of five practical diets containing 0, 50, 100, 200, or 400 AMP mg/kg diet for 14 weeks. Fish fed the AMP-free diet exhibited clinical signs of vitamin C deficiency and significantly poorer final average weight, specific growth rate, protein efficiency ratio, feed conversion ratio, and hematocrit level (p<0.05). The level of AA in the sea bass brain increased as the level of dietary AMP increased. The AA concentration in the liver was similar at all AMP dietary levels. Body calcium of sea bass fed the AMP-free or 50 mg diets was significantly lower (p<0.05) than in fish fed the other diets. AMP enhanced wound healing regardless of supplement level, but fish fed the highest dietary AMP (400 mg/kg diet) exhibited histopathological changes in the liver. The dietary level of 50 mg AMP/kg diet was adequate for optimum growth, liver AA saturation, and prevention of clinical signs of vitamin C deficiency in 80-220 g sea bass. However, 100 mg AMP per kg diet was necessary for optimum body calcium.

Replacement of fishmeal with rice protein concentrate in practical diets for European sea bassDicentrarchus labraxreared at winter temperatures

As no information is available regarding the efficacy of using rice protein concentrate (RPC) to replace fishmeal (FM) in diets for European sea bass (Dicentrarchus labrax), a trial was conducted to determine the optimum inclusion for European sea bass juveniles. Diets were formulated to replace 25%, 50% and 75% of fishmeal with RPC. Additional high level inclusion diets (50% and 75%) were supplemented with lysine and methionine to determine if these were limiting factors. Fish (18.0 ± 0.06 g) were fed the experimental diets for 12 weeks. The final mean weight and specific growth rate (SGR) were significantly higher in fish fed the control diet (diet FM) and low level RPC (diet RPC25) than in fish fed the other diets. The supplementation of the amino acids had a positive effect on growth, elevating the final weight of the high level RPC (RPC75 + AA) group above that of the non-supplemented group (RPC75). However, this was still not comparable to fish fed FM and RPC25 diets. No significant differences in body composition were observed. A digestibility study demonstrated an inverse relationship between elevating inclusion levels of RPC and apparent digestibility coefficients (ADCs) for dry matter and lipid, with significantly lower values than the control being observed with RPC inclusions above 25%. The mesenteric fat index followed this trend. Circulating leucocyte levels, leucocyte ratios and serum lysozyme activity remained unaffected by dietary treatment. However, compared with the control group, fish fed RPC75, RPC50 + AA RPC75 + AA displayed significantly lower haematocrit values. The present study demonstrates that the inclusion of RPC at 140 g kg−1 (effectively replacing 25% of FM content) does not compromise European sea bass growth performance, body quality or basic haematological parameters. It is suggested that future studies including higher levels test the efficacy of additional amino acid supplementation (e.g. tryptophan).

Predation of the juvenile stages of diadromous fish by sea bass (Dicentrarchus labrax) in the tidal reaches of an English chalk stream

Abstract The first incidence of predation by the sea bass (Dicentrarchus labrax) on lamprey ammocoetes and salmonid smolts is reported. These preliminary findings suggest that there is a need for further investigation to determine if juvenile diadromous fish form a significant component of the diet of sea bass, and to identify whether the likelihood of enhanced abundance of sea bass in protected nursery areas presents a particular threat to the conservation of Atlantic salmon (Salmo salar). This will require further sampling of the stomach contents of sea bass and estimates of the sea bass population in nursery areas to be determined, linked with an assessment of the impact of such predation on the conservation status of particular stocks of diadromous fish. © 2011 Crown copyright. Reproduced with the permission of her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Apparent digestibility coefficients of several protein sources, and replacement of fishmeal by porcine meal in diets of Japanese seabass, Lateolabrax japonicus, are affected by dietary protein levels

A digestibility and a growth trial were conducted in this study respectively. Firstly, the apparent digestibility coefficients (ADC) of nutrients and energy in meat and bone meal, porcine meal (PM), hydrolysed feather meal, poultry by-products meal, fishmeal (FM), soybean meal and spray-dried blood meal were determined. In experiment 2, an 8-week growth trial was conducted to evaluate the effects of the substitution of FM by PM under the digestible ideal protein concept at two protein levels in the diets of Japanese seabass, Lateolabrax japonicus. A FM-based control diet (FM diet; FM: 320 g kg−1, crude protein: 434.9 g kg−1, crude lipid: 124.6 g kg−1) and three other diets were formulated to contain 115 g kg−1 PM and only 160 g kg−1 FM. Two diets were formulated on a crude protein basis without (PM diet) or with (PMA diet) essential amino acid (EAA) supplementation respectively. A low-protein diet was designed (LPMA diet, crude protein: 400.9 g kg−1, crude lipid: 96.3 g kg−1) with the same level of FM and PM but with the same digestible protein/ digestible energy and EAA profile as the FM diet. The results showed that nitrogen and total amino acid digestibility of the tested ingredients were ranged from 85.6% to 95.5% and from 87.6% to 95.5% respectively. Apparent digestibility coefficients of protein for FM and PM were 91.2% and 95.9% respectively. In the growth trial, the weight gain rate and feed conversion ratio of fish fed the PMA diet did not show a significant difference from those of the control group, but were significantly higher than those of the PM and LPMA groups (P<0.05). Growth was related linearly to lysine and methionine intakes. It was shown that PM could be utilized in the Japanese seabass diet up to 115 g kg−1 to replace about 160 g kg−1 of FM protein under an ideal protein profile. Essential amino acid deficiency (diet PM) or a lower protein level despite having an ideal amino acid profile (diet LPMA) could not support the optimal growth of Japanese seabass.

α-Tocopherol in weaning diets for European sea bass (Dicentrarchus labrax) improves survival and reduces tissue damage caused by excess dietary DHA contents

The objective of the present study was to investigate the combined effect of several dietary contents of vitamin E and polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid (DHA), on growth, survival, biochemical composition and tissue morphology of sea bass along early development. A feeding experiment was conducted in sea bass larvae using five different diets with the same proximate composition and different ratios of DHA concentrated fish oil [10, 30 and 50 g kg−1 dry weight (DW)] and vitamin E (α-tocopherol acetate) (1500 and 3000 mg kg−1 DW). DHA was readily deposited in fish tissues and associated with higher sea bass mortalities probably because of increased peroxidation risks. Besides, the elevation of dietary DHA contents up to 5% severely increased the incidence of muscular lesions and the presence of ceroid pigment within hepatocytes. However, elevation of dietary vitamin E levels markedly reduced the incidence of these symptoms in sea bass, increasing the tissue content in several PUFA and improving growth and stress resistance. Moreover, when sea bass was fed diets containing high vitamin E levels, fish showed a significant improvement in growth when dietary DHA was raised from 1% to 3%. Therefore, in sea bass larvae, a ratio of 30 g kg−1 DHA and 3000 mg kg−1 vitamin E seems to be adequate to achieve a good larval performance and to avoid muscular lesions.

Wheat gluten as a partial substitute for fish meal protein in sea bass (D. labrax) diets

Previuos investigations have shown wheat gluten meal (WGM) to be a promising candidate ingredient to replace fish meal (FM) in sea bass diets, based on its high crude protein content and biavailability and the absence of antinutritional factors in the raw material (Robaina et al., 1999; Tulli and Tibaldi, 2001)...

The Effect of Partial Replacement of Dietary Fishmeal with Fermented Prawn Waste Liquor on Juvenile Sea Bass Growth

A feeding trial was conducted for 49 days to evaluate the effect of partially substituting fishmeal with fermented prawn waste liquor (FPWL) in juvenile sea bass diets at 10%, 20%, and 30% of the total diet. Growth performance of sea bass from 16 g up to 40 g fed with FPWL-supplemented diet was not significantly different from the all fishmeal control diet. The most cost-effective diet included FPWL at 30%, with weight gain, feed conversion ratio, and protein efficiency ratio of 180%, 1.78%, and 1.2% respectively.

Use of Yeast-Fermented Canola Meal to Replace Fishmeal in the Diet of Asian Sea Bass Lates Calcarifer (Bloch, 1790)

Fishmeal is a significant protein source for aquatic feed, especially for carnivorous fish. Currently, the price of fishmeal is increasing, also it is mentioned as a competition of human food fish. Replacing fishmeal by other protein sources is therefore an important target. This study tested yeast-fermented canola meal in the diet of Asian sea bass, Lates calcarifer to determine its effects on growth, feed acceptance, feed utilization, nutrient digestibility, body proximate, minerals and their utilization. Diets consisted of a 35% fishmeal base (control) and four diets in which fishmeal protein was replaced by yeast-fermented canola meal at levels of 25, 50, 75 and 100%. For each diet, three groups of fish with an initial weight of 5 g were fed to satiation twice a day for 60 days. Feed intakes and survival rates of test fish fed the diets with up to 50% replacement were not significantly different (P > 0.05). Fish fed the diet with 100% replacement rejected the feed and all died within two weeks. Fish fed the diet in which 75% of fishmeal protein replacement had lower final mean weight, daily weight gain, protein efficiency ratio, nutrient digestibility and higher feed conversion ratio (P < 0.01) than fish fed the control, 25% and 50% replacement diets. Increasing the protein replacement level lowered body crude protein, ash, Ca, Mg, P and their utilization of Asian sea bass (P < 0.05). This seemed to relate to increasing dietary phytic acid as the inclusion level of yeast-fermented canola meal increased. It was concluded that 50% of fishmeal in the diet of Asian sea bass could be replaced by yeast-fermented canola meal without overall impact on growth. This study also showed the possibility of < 10% dietary fishmeal for this species since fish accepted a diet containing only 8.75% fishmeal.

Reduced gut bacterial translocation in European sea bass ( Dicentrarchus labrax) fed mannan oligosaccharides (MOS)

The objective of this study was to determine the effect of mannan oligosaccharides derived from the outer cell wall of a select strain of Saccharomyces cerevisiae (Bio-Mos, Alltech Inc, USA) on mucus production, selected mucus immune parameters activity, gut morphology and in vivo and ex vivo gut bacterial translocation for European sea bass ( Dicentrarchus labrax). Specimens were fed 4 g kg −1 dietary MOS level of inclusion in a commercial sea bass diet for eight weeks. At the end of this period, anterior gut mucosal folds height, width and folds surface area were increased by MOS supplementation ( P < 0.05, n = 240). Posterior gut presented shorter folds ( P < 0.05, n = 240) but wider that those fed control diet ( P < 0.05, n = 240) resulting in increased total surface area ( P < 0.05, n = 240). For rectum, feeding MOS reduced fold length ( P < 0.05, n = 240). Gut morphological analyses showed an enhancement in the number of cells secreting acid mucins by area unit, higher density of eosinophilic granulocytes (ECGs) in the mucosa for fish fed MOS together with an improvement in gut mucus lysozyme activity which could be related to the reduced in vivo and ex vivo gut bacterial translocation found. No differences were found for the skin mucus immune parameters evaluated.

Development of a Practical Soy‐Based Diet for White Seabass

AbstractTwo feeding trials were conducted to begin development of a practical soy‐based diet for white seabass Atractoscion nobilis. The first trial was designed to provide initial data on the efficacy of practical soy‐based diets. Three diets and a commercial reference diet were evaluated. Research diets were 42% protein and 12% lipid, with varying protein sources: fish meal (FM), FM plus solvent‐extracted soybean meal (SBM), or FM plus soy protein concentrate (SPC). Final weight (14.1–17.2 g), percent weight gain (307.2–401.8%), and feed conversion ratio (FCR; 1.0–1.2) followed similar trends, with fish offered the FM‐based diet significantly outperforming the other dietary treatment groups. There was no significant difference between soy‐based diets and the commercial reference diet, and no significant differences in survival due to dietary treatments were observed. The second trial was designed to evaluate varying levels of FM replacement with SPC in a series of four diets containing 42% protein and 12% lipid. The basal diet contained 40% FM and 24.6% SBM as primary protein sources. The FM was then reduced to 30, 20, and 15% of the diet using SPC as the replacement protein. Final weight (27.1–36.5 g), percent weight gain (69.0–116.6%), and FCR (1.5–2.4) followed similar trends, with performance decreasing as FM level was reduced. In general, each incremental reduction in FM resulted in significant reductions in final weight and percent weight gain and significant increases in FCR. Results from these initial trials on white seabass are encouraging because the poor response was most likely due to a nutrient imbalance or palatability problem, which can be corrected, as opposed to an allergic response. Given that the open formulations performed similarly to the commercial feed, these simple formulations can be used as a starting point for the development of practical diets for white seabass.

Regulation of FADS2 expression and activity in European sea bass (Dicentrarchus labrax, L.) fed a vegetable diet

Supplies of marine fish oils are limited, and continued growth in aquaculture production dictates that lipid substitutes in fish diets must be used without compromising fish health and product quality. In this study, the total substitution of a fish meal and fish oil by a blend of vegetable meals (corn, soybean, wheat and lupin) and linseed oil in the diet of European sea bass (Dicentrachus labrax) was investigated. Two groups of European sea bass were fed with fish diet (FD) or vegetable diet (VD) for 9months. VD, totally deprived of eicosapentaenoate (EPA; 20:5n-3) and docosahexaenoate (DHA; 22:6n-3), revealed a nutritional deficiency and affected growth performance. Whilst VD induced a significant increase in fatty acid desaturase 2 (FADS2) and sterol binding regulatory element-binding protein 1 (SREBP-1) mRNA levels, the desaturation rate of [1-(14)C]18:3n-3 into [1-(14)C]18:4n-3, analysed in microsomal preparations using HPLC method, did not show an upregulation of FADS2 activities in liver and intestine of fish fed VD. Moreover Western-blot analysis did not revealed any significant difference of FADS2 protein amount between the two dietary groups. These data demonstrate that sea bass exhibits a desaturase (FADS2) activity whatever their diet, but a post-transcriptional regulation of fads2 RNA prevents an increase of enzyme in fish fed a HUFA-free diet. This led to a lower fish growth and poor muscle HUFA content.

Soybean Meal and Rendered Animal Protein Ingredients Replace Fishmeal in Practical Diets for Sea Bass

A 180-day feeding trial was carried out in net cages to examine replacement of fishmeal with soybean meal supported by meat/bone meal and blood meal in practical diets for sea bass (Dicentrarchus labrax L. 1758). Triplicate groups of fish (initial body weight 110 g) were fed one of four isonitrogeneus (crude protein 46%) and isolipidic (10%) diets. A commercial sea bass diet containing 64% fishmeal as the sole animal protein served as the control. The other three diets contained 0, 20%, or 35% fishmeal and the reduced fishmeal was replaced by different levels of soybean meal, meat/bone meal, and blood meal. The final body weight of fish fed the diet containing 20% fishmeal, 50% soybean meal, 10% meat/bone meal, and 4% blood meal was significantly higher than that of the other three treatments. Results indicate that fishmeal can be reduced to 20% when soybean meal, meat/bone meal, and blood meal are used together in the diet.

Growth, feed utilization, health and organoleptic characteristics of European seabass ( Dicentrarchus labrax) fed extruded diets including low and high levels of three different legumes

Three legumes [field peas (P), chickpeas (CP) and faba beans (B)] were evaluated at two inclusion levels; 170 (L) and 350 g kg − 1 (H) in a 14-week experiment with triplicate groups of 97.9 ± 6.1 g European seabass. A control diet included wheat meal, fish meal (FM) and a mixture of plant ingredients as protein sources. Diets, processed in a twin-screw extruder, were isonitrogenous and isoenergetic. All experimental diets improved growth compared to the control. Weight gain, feed intake, FCR and SGR were improved for fish fed diet CPL, while fish fed diet CPH gave higher FCR. Protein and starch digestibility were highest for the control diet, while fish fed diets CPL and PL showed significantly lower protein ADCs and lower starch ADC ( P ≤ 0.05) for diet PH. Among H diets, significantly better fillet yield was found for fish fed diet PH, but no other differences were found in seabass fillet organoleptic characteristics. Serum glucose and cholesterol were elevated in fish fed CP diets, while protein and triacylglycerols did not show significant differences among treatments. Fish fed the test diets showed no significant evidence of either immunosuppression or immunostimulation. Histology of liver, spleen, kidney and foregut revealed no pathological abnormalities. Field peas, chickpeas and faba beans can be included in European seabass diets up to 350 g kg − 1 substituting for wheat with no negative effects on growth performance, carcass composition or organoleptic characteristics.

Effects of in vitro lactoferricin and lactoferrin on the head kidney cells of European sea bass ( Dicentrarchus labrax, L.)

Antimicrobial, anti-inflammatory and immunomodulating properties of lactoferrin have been demonstrated in mammals and in fish. However, in vivo, lactoferrin is digested by gastric pepsin treatment into the N-terminal derived peptide named lactoferricin. This has been so far overlooked in fish in vitro studies. The aim of the present study was to assess in vitro the effects of both lactoferricin and lactoferrin on the head kidney cells of European sea bass ( Dicentrarchus labrax, L.) in order to determine their potential as dietary additives and to get some insight into their mode of action. In vitro lactoferricin decreased significantly the chemiluminescent response of head kidney cells but did not affect the zymosan-triggered chemiluminescence activity. On the other hand, a high concentration of lactoferrin directly stimulated chemiluminescence but reduced the zymosan-triggered chemiluminescence. The bactericidal activity of head kidney cells was also significantly diminished by pre-incubation with lactoferrin in a dose-dependent manner. Although no significant effect of lactoferricin or lactoferrin was evidenced on head kidney cellular viability, absent or negative effect on the priming of respiratory burst activity suggested that care should be taken when using lactoferrin in the diet of sea bass and high doses should be avoided. Hypotheses about the mechanisms of action of lactoferricin and lactoferrin are presented.

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Aquaculture ResearchVolume 40, Issue 3 p. 384-384 Free Access ERRATA This article corrects the following: A preliminary study on the utilization of hazelnut meal as a substitute for fish meal in diets of European sea bass (Dicentrarchus labrax L.) Yılmaz Emre, Hüseyin Sevgili, Murat Şanlı, Volume 39Issue 3Aquaculture Research pages: 324-328 First Published online: January 24, 2008 First published: 22 January 2009 https://doi.org/10.1111/j.1365-2109.2008.02090.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In Aquaculture Research 39:3, the following errors were published on page 325: Was incorrect and should have been feed conversation ratio (FCR)=weight gain/feed consumed Was incorrect and should have been feed conversion ratio (FCR)=dry feed consumed/weight gain On page 327, the following error was published: Because 30% was the maximum incorporation level of HM, this hampered us in estimating the level of HM that can be incorporated into European sea diets instead of FM. This sentence was incorrect and should have read: Because 30% was the maximum incorporation level of HM, this hampered us in estimating the level of HM that can be incorporated into European sea bass diets instead of FM. We apologize for these errors. Reference Emre Y., Sevgili H. & Şanlι M. (2008) A preliminary study on the utilization of hazelnut meal as a substitute for fish meal in diets of European sea bass (Dicentrarchus labrax L.). Aquaculture Research 39, 324– 328. doi: 10.1111/j.1365-2109.2007.01881.x. Wiley Online LibraryCASWeb of Science®Google Scholar Volume40, Issue3February 2009Pages 384-384 ReferencesRelatedInformation

Apparent nutrient digestibility and gastrointestinal evacuation time in European seabass ( Dicentrarchus labrax) fed diets containing different levels of legumes

Nutrient digestibility and gastrointestinal evacuation time for diets containing two levels of legumes were determined in European seabass (initial wt. 150 g). Seven isonitrogenous (44 g crude protein 100 g − 1 ) and isoenergetic (20 kJ g − 1 ) extruded diets were tested. Experimental diets contained 15 g or 30 g 100 g − 1 of each legume including faba bean meal, (FB15, FB30), chickpea meal (CP15, CP30), field pea meal (FP15, FP30) and a control, wheat meal containing, diet. Inclusion of faba beans in diets significantly enhanced apparent digestibility coefficients (ADCs) of dietary protein and energy at both inclusion levels. Starch digestibility was significantly lower for the control and FP30 diet and significantly higher for the FB15 diet. Fat digestibility coefficients were elevated significantly for FB15, FB30, CP15, FP15 and FP30 diets, compared to the CP30 and the control diet. The incorporation of faba bean and chickpea greatly affected gastrointestinal evacuation time compared to fish fed the control diet. Longer passage times were observed when these legumes were included in the diet. Glucose serum peak value was delayed for FB30 and a slower decreasing rate was observed for the legume diets. The addition of legumes had a positive effect on physical properties of the pellets by increasing the hardness while water activity remained within the safety limits. The findings of this study suggest that the legumes tested are potential candidates for carbohydrate replacement (wheat) and, to a lesser extent, for protein substitution in diets for European seabass.

Estuarine colonization, population structure and nursery functioning for 0-group sea bass (Dicentrarchus labrax), flounder (Platichthys flesus) and sole (Solea solea) in a mesotidal temperate estuary

The function of the Mondego estuary as a fish nursery habitat was investigated from June 2003 to June 2004 by comparing the timing of estuarine colonization with juveniles of sea bass Dicentrarchus labrax, flounder Platichthys flesus, and sole Solea solea, while also analysing their population structure, growth and diet composition. Differences in the onset of estuarine colonization were observed, since sole juveniles were the first to enter the estuary (in January), followed by flounder in April and sea bass in June. The estuarine population of these species consisted of several age-groups, although the majority of individuals belonged to age-groups 0 and 1. The growth rates determined for 0-group fish were within the range of those reported for other European estuarine systems. Some differences were also recognized regarding the timing of estuarine colonization and the length of the growing season. Diet of 0-group sea bass consisted mainly of Crustacea, Polychaeta and Mollusca. Flounder juveniles fed chiefly on Amphipoda (especially Corophium spp.), with Polychaeta, Isopoda and Decapoda also being common prey. The diet of 0-group sole was dominated by Polychaeta, with Amphipoda, Mollusca and Decapoda ranking highest, with other important benthic organisms also being present. Dietary overlap among these species was relatively low.

Immune stimulation and improved infection resistance in European sea bass ( Dicentrarchus labrax) fed mannan oligosaccharides

The objective of this study was to determine the effect of two levels of inclusion of mannan oligosaccharides derived from the outer cell wall of a select strain of Saccharomyces cerevisiae (Bio-Mos, Alltech Inc, USA) on growth, feed utilization, immune status and disease resistance of European sea bass ( Dicentrarchus labrax). Specimens of 35 g at initial density of 3 kg/m 3 were fed during 67 days at 0‰, 2‰ and 4‰ dietary MOS level of inclusion in a commercial sea bass diet. Food conversion rate, specific growth rate, whole body biochemical composition, phagocyctic index of head kidney macrophages, NBT index, lysozyme and alternative complement pathway (ACP) activities as well as gut and liver histological structure were evaluated. Growth significantly increased at both MOS dietary inclusion levels. Histological features of the liver showed lower lipid vacuolization and regular-shaped morphology of hepatocytes around the sinusoidal spaces denoting a better utilization of dietary nutrients. No differences were found on gut histological evaluation. Statistical differences ( P < 0.05) on the phagocytic index were denoted with the inclusion of 4‰ Bio-Mos group. A positive correlation was found between the levels of lysozyme and alternative complement pathway activities in blood and the level of inclusion of MOS in diets. After the feeding trial, a cohabitation challenge test and direct gut inoculation were also performed with the pathogen Vibrio alginolyticus in a ratio 3:1. Twenty-one days post-challenge the number of cohabitant fish infected in the control group reached 33% comparing with none on the 0.4‰ MOS group. Finally, new fish were infected with V. alginolyticus by gut canalisation. After 24 h post-infection no significant difference was denoted between groups and 48 h post-infection total infected fish in the control group was twice that of the 2‰ and 4‰ MOS groups.