L. Robaina

Soybean and lupin seed meals as protein sources in diets for gilthead seabream (Sparus aurata) : nutritional and histological implications

The use of vegetable protein sources in diets for freshwater fish has been studied in more detail than for marine fish species. Two experiments were conducted to compare the effect of the partial substitution of fish meal by two different vegetable protein sources, soybean and lupin seed meals. Mean feed intake and growth were not significantly influenced by type or level of plant protein in the diet. Feed utilization indexes such as feed efficiency, protein efficiency ratio and protein productive values were not significantly affected by the type of plant protein in the diet, although a general reduction of these values was observed with increased inclusion of soybean meal. Histological studies showed an increased deposition of lipid and decreased glycogen deposits in the liver with increased levels of dietary soybean meal. Protein digestibility coefficients for lupin seed meal diets were similar to the control and 10% higher than those for the soybean meal diets. A significant reduction in trypsin activity was observed in fish fed the lupin seed meal diets, and for soybean meal diets when the substitution level reached 30%. Diets including plant protein showed a higher peak of ammonia excretion rate, which appeared 2 h later than that of the fish meal diet. Highest values of dissolved ammonia were registered in fish fed a soybean meal-based diet. These results suggest that properly treated lupin meals could be an important alternative dietary protein source for gilthead seabream.

Vegetable lipid sources for gilthead seabream (Sparus aurata): effects on fish health

Abstract Commercial feeds for gilthead seabream are highly energetic, containing fish oil as the main lipid source. The steady production and raising prices of fish oil encourage the inclusion of vegetable oils in fish feeds. Fish oil could be at least partially substituted by vegetable oils in diets for marine species, being this substitution resulted in good feed utilization and maintenance of fish health, since imbalances in dietary fatty acids may alter the immunological status and stress resistance in fish. In order to evaluate the effect of vegetable oils on gilthead seabream health, fish were fed different isonitrogenous and isocaloric diets for 101 days (Experiment I) and 204 days (Experiment II). In Experiment I, diets were formulated to contain 60% of the fish oil used in the control diet (FO) as soybean oil (Diet 60SO), rapeseed oil (60RO), linseed oil (60LO) or a blend of those oils (Mix). In Experiment II, the same diets plus two which contained 80% of the fish oil as soybean oil (80SO) and linseed oil (80LO), respectively, were assayed. At the end of both experiments, basal levels of different immunological parameters were determined, including both humoral immunity (alternative complement pathway activity and serum lysozyme activity) and cellular immunity (circulating neutrophil activity and phagocytic index of head kidney macrophages). In addition, response to a confinement stress was assayed in terms of variations in plasma cortisol. The effect of dietary vegetable oils on fatty acid composition of head kidney macrophages and circulating red blood cells (RBC) was also studied. No effects of dietary vegetable oils were found in fish fed the experimental diets for a medium period. Feeding dietary vegetable oils for a long period did not affect lysozyme or neutrophil activity. However, in Experiment II, the inclusion of soybean oil reduced both serum alternative complement pathway activity (from 249 IU/ml (FO2) down to 153.8 IU/ml (60SO2)) and head kidney phagocytic activity (from 25.75% (FO2) down to 14.58% (80SO2). Inclusion of rapeseed oil reduced phagocytic activity. Fish fed vegetable oil-containing diets showed different patterns of stress response, especially those fish fed the linseed oil diets that showed a significant increase in plasma cortisol level after stress. The fatty acid composition of head kidney macrophages reflected the fatty acids content of the respective diets, but a selective incorporation of essential fatty acids into these cells was observed. The same trend was found in circulating red blood cells, indicating the important role of essential fatty acids on these cells. Sixty percent of fish oil can be replaced by a blend of different vegetable oils without affecting gilthead seabream health. However, if single vegetable oil is used to replace 60% of fish oil, fish health can be affected in terms of immunosuppression or stress resistance. Rapeseed oil affected head kidney macrophages activity, soybean oil affected serum alternative complement pathway activity and linseed oil altered stress response of fish.

Corn gluten and meat and bone meals as protein sources in diets for gilthead seabream (Sparus aurata): Nutritional and histological implications

Abstract Two experiments were conducted to compare the effect of the partial substitution of fish meal by two different protein sources, corn gluten (CGM) and meat and bone meals (MBM) in diets for juveniles gilthead seabream. Growth, feed efficiency, protein efficiency ratio and protein productive values were not significantly affected by the source of dietary protein, although higher values were observed with diets containing increasing levels of meat and bone meal. No differences were found in fish proximate composition at the end of the experiment. Histological studies of liver tissue showed no liver alteration in fish fed diets including increasing levels of corn gluten meal. On the contrary, an increased deposition of lipids, nuclei polarization and isolated necrotic focus were found in hepatocites of fish fed diets exceeding 20% of meat and bone protein. Apparent protein digestibility (ADC) in diets containing CGM showed similar results to those obtained with the control diet. However, a significant reduction in digestibility was observed when MBM was used as partial substitute of fish meal protein. A negative correlation between dietary ash content and protein digestibility was observed. Higher amounts of nitrogen were excreted as levels of CGM and MBM increased in the diets, being significantly higher in the case of 40% substitution either with CGM or MBM protein.

Adaptation of lipid metabolism, tissue composition and flesh quality in gilthead sea bream ( Sparus aurata ) to the replacement of dietary fish oil by linseed and soyabean oils

Linseed (LO) and soyabean (SO) oils were evaluated as fish-oil (FO) substitutes in the diets of marketable-sized gilthead sea bream (Sparus aurata). Practical diets were designed factorially with the lipid added as follows (%): FO 100, LO 60+FO 40, LO 80+FO 20, SO 60+FO 40, SO 80+FO 20. The effects of experimental diets on growth, fatty acids patterns in liver and muscle, flesh quality variables and activities of selected enzymes involved in lipid synthesis and catabolism were determined at the end of a 7-month trial. Fatty acid composition of liver and muscle generally reflected the fatty acid composition of the diets. The n-3 PUFA levels were significantly reduced by the inclusion of vegetable oils. This tendency was more pronounced for EPA than for docosahexaenoic acid. The n-3:n-6 fatty acid ratio reached the lowest values in fish fed the SO diets; this was associated with a higher liver lipid deposition. No differences were found in fillet texture and pH. However, under conditions of forced peroxidation, muscles from fish fed the SO diets had lower peroxidation levels. Vegetable oil substitution decreased lipogenesis in liver and this effect was greatest at the highest substitution level. In contrast, muscle beta-oxidation enzymes had increased activities with vegetable oil substitution. Thus, the lower hepatic lipogenesis was correlated with an increased lipid utilisation in muscle. It is concluded that growth and lipid metabolism were affected by experimental diets.

Effect of vitamin E and C dietary supplementation on some immune parameters of gilthead seabream (Sparus aurata) juveniles subjected to crowding stress

Abstract High stocking density is an aquaculture-related situation which causes crowding stress in fish and potentially affecting the immune system. Protection against disease can be induced through immunostimulation, enhancing defence mechanisms. Vitamins C and E are among the most important nutrients influencing the immune system, although the effect of these vitamins in the amelioration of stress in fish has not been studied in detail. An experiment was carried out to study the effect dietary supplementation of vitamin C or vitamin E on the immune system of fish under a crowding stress situation in a commercial farm. A commercial diet for this species was supplemented with vitamin C or vitamin E and these diets were assayed at high stocking density (over 40 kg m−3) and the results were compared with those from fish fed the commercial diet and held at farm conditions (20 kg m−3). Some biological and immunological parameters were studied at the end of the experimental period. Fish held at high stocking density showed lower final weight than fish held at lower stocking density. These also showed higher plasma cortisol levels (over 6 ng cortisol ml−1 plasma for all the diets assayed) than those fish held at lower density (1.13 ng cortisol ml−1 plasma). High stocking density produced higher serum lysozyme activity values in fish fed the commercial diet compared with those fish held at lower density (67.49 and 36.84 units ml−1, respectively). This effect was not observed in fish held at high stocking density but fed vitamin C and vitamin E supplemented diets (lysozyme activity: 21.97 and 19.71 units ml−1, respectively). High stocking density also appeared to decrease serum alternative complement activity. In those fish fed the vitamin E supplemented diet, levels were similar to fish held at low stocking density, suggesting the role of this vitamin in this defense mechanism.

Growth, feed utilization and body lipid content of gilthead seabream (Sparus aurata) fed increasing lipid levels and fish meals of different quality

The present study shows the effects of feeding gilthead seabream, 70 to 400 g, with nine diets containing three different lipid levels (15, 22 and 28% on a dry weight basis), combined with two types of fish meal of different quality. In addition, feed processing effects (extruded vs. pelletized) were also compared for the diet containing 22% lipid. The diets prepared with the high quality fish meal promoted better growth than those prepared with the low quality one. Protein utilization was enhanced by a sparing effect of dietary lipid at 22%. This lipid level needed to be increased up to 28% with low quality meal to effectively spare dietary protein. A significant increase in fish growth with higher dietary lipid levels, in both high and low quality fish meal diets, was only related to a significant increase in total body lipid content in high quality fish meal diets, and an excess of lipid may have been the cause of hepatocyte abnormalities in fish fed the highest lipid levels. The effect of pellet processing was apparent in low quality fish meal diets, where a significantly better growth performance was obtained in fish fed the extruded diet. There were no significant differences among all treatments in feed intake, and values were similar to those suggested by commercial fish feed producers, for similar fish size and water temperatures. Values for feed conversion ratio (FCR) were lower than 1.6 for all diets.

Increase of the dietary n - 3/n - 6 fatty acid ratio and addition of phosphorus improves liver histological alterations induced by feeding diets containing soybean meal to gilthead seabream, Sparus aurata

Abstract In a previous study, several histological alterations were found in the liver of gilthead seabream fed with a diet containing 30% soybean meal (SBM). In the current study, SBM containing diets were supplemented with either potassium phosphate, zinc sulfate or phytase ( Aspergillus ficuum ), or increasing the dietary n −3/ n −6 fatty acids ratio to meet that of a fish meal based diet. Diet composition did not affect fish growth, feed efficiency (FE) or protein productive value (PER). Phosphorous supplementation significantly reduced hepatosomatic indexes (HSI), although it did not alter liver lipid content. Both phosphorous supplementation and correcting the dietary n −3/ n −6 fatty acid ratio significantly altered the lipid and protein content in fish muscle. Only these two treatments and principally the corrected dietary n −3/ n −6 fatty acid ratio, improved the liver histological alterations observed in fish fed with SBM based diets.

Influence of fish meal quality and feed pellet on growth, feed efficiency and muscle composition in gilthead seabream (sparus aurata)

Abstract The effect of fish meal quality on growth, feed efficiency, protein digestibility and fillet composition was studied in a growth experiment with gilthead seabream. The experiment included a comparison of pelleted feed with extruded feed. The fish were fed three extruded diets which varied in the quality of the fish meal used in the respective feeds: low quality fish meal, good quality fish meal, and a mixture (50%) of the two fish meal qualities. Fish meal quality was judged by protein digestibility as measured with mink as the test animal and by the content of biogenic amines. A fourth experimental group was fed a pelleted feed with the same mixed fish meal blend. The experiment started with 70 g seabream and lasted for 3 months until the fish reached about 160 g. All groups showed good growth and feed efficiency during the experimental period, with daily specific growth rates (SGR) of 0.90–1.00% and feed efficiencies (FE; fish weight gain per feed offered) from 0.58 to 0.66. The fish fed the feed with low quality fish meal showed significantly poorer feed efficiency than the other groups, and there was a significant correlation between feed efficiency obtained in seabream and the protein digestibility as measured with mink. No difference was observed among groups fed the extruded diets, for growth, fillet composition or amount of liver or viscera, although a significant correlation was obtained between SGR and protein digestibility in mink. Fillet lipid content was higher in fish fed the extruded feed, compared with those fed the corresponding pelleted diet. Protein digestibilty in seabream showed no difference among the extruded feeds, while the pelleted feed was significantly lower.

Vegetable lipid sources affect in vitro biosynthesis of triacylglycerols and phospholipids in the intestine of sea bream (Sparus aurata).

Despite the good growth performance of several fish species when dietary fish oil is partly replaced by vegetable oils, recent studies have reported several types of intestinal morphological alterations in cultured fish fed high contents of vegetable lipid sources. However, the physiological process implied in these morphological changes have not been clarified yet, since alterations in the physiological mechanisms involved in the different processes of lipid absorption could be responsible for such gut morphological features. The objective of the present study was to investigate the activities of reacylation pathways in fish, the glycerol-3-phosphate and the monoacylglycerol pathways, in order to clarify the intestinal triacylglycerol (TAG) and phospholipid biosynthesis to better understand the morphological alterations observed in the intestine of fish fed vegetable oils. Intestinal microsomes of sea bream fed different lipid sources (fish, soyabean and rapeseed oils) at three different inclusion levels were isolated and incubated with L-[(14)C(U)]glycerol-3-phosphate and [1-(14)C]palmitoyl CoA. The results showed that in this fish species the glycerol-3-phosphate pathway is mainly involved in phospholipid synthesis, whereas TAG synthesis is mainly mediated by the monoacylglycerol pathway. Feeding with rapeseed oil reduced the reacylation activity in both pathways, explaining the high accumulation of lipid droplets in the supranuclear portion of the intestinal epithelium, whereas soyabean oil enhanced phosphatidylcholine synthesis, being associated with the increase in VLDL found in previous studies.

Effects of dietary concentrated mannan oligosaccharides supplementation on growth, gut mucosal immune system and liver lipid metabolism of European sea bass (Dicentrarchus labrax) juveniles.

The study assesses the effects of dietary concentrated mannan oligosaccharides (cMOS) on fish performance, biochemical composition, tissue fatty acid profiles, liver and posterior gut morphology and gen expression of selected parameters involved on the intestinal immune response and liver lipid metabolism of European sea bass (Dicentrarchus labrax). For that purpose, specimens of 20 g were fed during 8 weeks at 0 and 1.6 g kg(-1) dietary cMOS of inclusion in a commercial sea bass diet. Dietary cMOS enhanced fish length, specific and relative growth without affecting tissue proximate composition. However, cMOS supplementation altered especially liver and muscle fatty acid profiles by reducing levels of those fatty acids that are preferential substrates for β-oxidation in spite of a preferential retention of long chain polyunsaturated fatty acids (LC-PUFA), such as 20:4n-6 or 22:5n-6, in relation to the down-regulation of delta 6/5 desaturase gene expression found in liver. Besides, dietary cMOS supplementation reduced posterior gut intestinal folds width and induced changes on the gene expression level of certain immune-related genes mainly by down regulating transforming growth factor β (TGFβ) and up-regulating immunoglobulin (Ig), major histocompatibility complex class II (MHCII), T cell receptor β (TCRβ) and Caspase 3 (Casp-3). Thus, dietary cMOS inclusion at 0.16% promoted European sea bass specific growth rate and length, stimulated selected cellular GALT-associated parameters and affected lipid metabolism in muscle and liver pointing to a higher LC-PUFA accumulation and promoted β-oxidation.