Plant Protein-based Diets Research Articles

Modulation of the IgM gene expression and IgM immunoreactive cell distribution by the nutritional background in gilthead sea bream (Sparus aurata) challenged with Enteromyxum leei (Myxozoa)

The aim of the present work was to determine if a plant protein-based diet containing vegetable oils (VO) as the major lipid source could alter the distribution of IgM immunoreactive cells (IRCs) and the IgM expression pattern in the intestine and haematopoietic tissues of gilthead sea bream (GSB) (Sparus aurata) challenged with the myxosporean Enteromyxum leei. In a first trial (T1), GSB fed for 9 months either a fish oil (FO) diet or a blend of VO at 66% of replacement (66VO diet) was challenged by exposure to parasite-contaminated water effluent. All fish were periodically and non-lethally sampled to know their infection status. After 102 days of exposure, samples of intestine and head kidney were obtained for IgM expression and immunohistochemical detection (IHC). Additional samples of spleen were taken for IHC. Fish were categorized as control (C, not exposed), and early (E), or late (L) infected. The 66VO diet had no effect on the number of IgM-IRCs in any of the tissues or on IgM expression in C fish, whereas the infection with E. leei had a strong effect on the intestine. A combined time-diet effect was also observed, since the highest expression and IRCs values were registered in the posterior intestine (Pi) of E-66VO fish. A positive correlation was found between IgM expression and the presence of IgM-IRCs in the Pi. The effect of the time of infection was studied more in detail in a second trial (T2) in which samples of Pi were taken at 0, 24, 51, 91 and 133 days after exposure to the parasite. A significant increase of the IgM expression was detected only in parasitized fish, and very late after exposure. These results show that the duration of the exposure to the parasite is the most determinant factor for the observed intestinal IgM increased phenotype which gets magnified by the feeding of a high VO-based diet.

Microarray analysis of differential utilization of plant-based diets by rainbow trout

Microarray analysis was conducted using liver samples from two families of rainbow trout that differed in their growth responses when compared between individuals fed a fishmeal or plant protein-based diet. Differential expression relating to dietary utilization between the two families found significant changes in expression of 33 expressed sequence tags (ESTs). Eight of the differentially expressed ESTs had identified mammalian homologs that had been previously researched with identified cellular interactions and functions. Utilizing pathway analysis software to analyze sequences annotated with known mammalian genes, we were able to map gene pathways and process interactions. From this information, we were able to infer that the metabolic changes associated with utilization of plant protein versus fishmeal were associated with differential regulation of genes related to cell oxidative stress, proliferation, growth and survival. Furthermore, we inferred from the changes we observed in immune response gene expression that ingestion of this plant-based diet upregulated the expression of genes involved in immunoregulatory processes.

Factors affecting nutrient digestibility in rainbow trout (Oncorhynchus mykiss) fed a plant protein-based diet supplemented with microbial phytase

Factors influencing apparent digestibility coefficient (ADC) of nutrients from a plant protein–based diet supplemented with microbial phytase were investigated in a series of experiments with rainbow trout (Oncorhynchus mykiss). The influence of phytase level, water temperature, feed particle size and addition of a protease/non-starch polysaccharidase (PNSP) enzyme cocktail were tested in a phytase-supplemented (2000 FTU kg−1) diet. Finally, the influence of Ca/P ratio, addition of 1,25-hydroxycholeocalciferol, or inclusion of lactic acid (LA) in diets with and without phytase was evaluated. Addition of microbial phytase improved ADC of dry matter (DM), protein, ash and minerals (P, Ca, Mg, Fe and Zn) (P < 0.05). Reducing feed particle size potentiated the effect of phytase on P and ash ADC, as did the addition of a PNSP enzyme cocktail; the latter also significantly improved DM ADC in both control and phytase-supplemented diets. Increasing the Ca/P ratio reduced the effect of phytase on P and ash ADC. Addition of 1,25-dihydroxycholecalciferol and LA had no effect on DM, P and ash ADC in control diets and tended to reduce the phytase-induced increase in P ADC.

Replacement of fishmeal by increasing levels of plant protein blends in diets for Senegalese sole ( Solea senegalensis) juveniles

A growth trial was conducted to evaluate the growth potential and nutrient utilization of Senegalese sole fed diets containing increasing replacement levels of dietary fishmeal (FM) by mixtures of plant protein (PP) sources. Six extruded isonitrogenous and isolipidic diets (55% crude protein and 8% crude fat on a dry matter basis) were fed to juvenile sole (mean initial body weight: 8 g ± 0.06) during 92 days. A reference diet containing FM as the main protein source (Control) was compared with five PP based-diets with increasing PP levels: 25% (PP25), 35% (PP35), 45% (PP45), 60% (PP60) and 75% (PP75). PP45, PP60 and PP75 diets were supplemented with crystalline amino acids to simulate the level present in the Control diet. The environmental impact of the tested diets was assessed through the determination of N and P budgets and calculating approximate Fish-in:Fish-out (Fi:Fo) ratios. Fish fed PP25 and PP75 reached a final body weight and daily growth index (DGI) similar to the Control group (P > 0.05). Diet PP45 displayed the lowest DGI (0.8 vs 1.3%), lowest protein efficiency ratio (1.03 vs 1.8) and highest FCR (1.7 vs 1.01). The dietary treatments with highest percentage of FM replacement (PP60 and PP75) displayed similar FCR values as the Control (1.2–1.0). Apparent digestibility coefficients (ADCs) of protein varied between 77 and 85% and were not significantly affected by the PP inclusion level. Whole body protein and energy content did not differ significantly among treatments, but protein gain was significantly higher in the Control group compared to PP35, PP45 and PP60 groups. The results indicate that Senegalese sole can effectively cope with plant protein-based diets, but growth rate and nutrient gain mainly depend on the selection of adequate plant protein blends, rather than on the plant protein incorporation level. Sole fed the highest PP level (PP75) showed good growth performance, efficient dietary nutrient utilization and a lower Fi:Fo ratio compared to the Control. The present results clearly show that increasing FM replacement level can have a positive environmental impact as reduces P fecal waste and the fishmeal used per kg of sole produced.

Impact of dietary plant protein levels on the volatile composition of Senegalese sole (Solea senegalensis Kaup, 1858) muscle

The present study evaluates the possible effects of dietary protein sources on Senegalese sole muscle volatile compounds. Senegalese sole juveniles (8g mean IBW) were fed with six extruded diets containing different protein sources: a control diet contained fish meal as the main protein source and five plant protein-based diets, in which fishmeal was replaced by increasing levels of a blend of vegetable proteins: soybean, pea, potato, wheat and corn gluten at five graded levels. The volatile profiling of the raw fish fillets was evaluated using automated HS-SPME coupled to GC–MS. Thirty-five compounds were identified and the most abundant in all samples were quantified. 1-Penten-3-ol, hexanal, 1-octen-3-ol and (E)-2-nonen-1-ol were present in the highest concentrations. Among the 20 compounds quantified, no major differences were observed in muscle volatile profile of fish fed with the different diets (p>0.05). These findings indicated that fish meal substitution by plant proteins has no major effects on sole’s muscle volatile composition.

Encapsulation of microbial phytase: Effects on phosphorus bioavailability in rainbow trout (Oncorhynchus mykiss)

This study was undertaken to investigate the effects of adding microbial phytase to plant protein-based diets for rainbow trout (Oncorhynchus mykiss). A plant protein-based basal diet was formulated to be isonitrogenous, isolipidic and isoenergetic to a nutrient-dense, fish meal-based control diet (Starter salmonid diet; Ontario Ministry of Natural Resources (MNR), University of Guelph). The basal plant protein-based diet was supplemented with 3000FTU microbial phytase kg−1 included either in a free form or encapsulated in chitosan-alginate microcapsules. A second control group was fed the basal plant protein-based diet supplemented with monosodium phosphate to NRC requirements. Apparent digestibility coefficients (ADC) were determined for dry matter, energy, protein, ash, P, Ca, Mg, Mn, Cu, Zn and Fe. The above diets were fed to triplicate tanks of rainbow trout for 56 days; growth and feed efficiency were monitored at 2-week intervals. At the start of the study and at 28-day intervals, fish were sampled to determine composition of the whole carcass and tissues and blood concentration of inorganic P. Proteolytic enzyme activity in intestine was measured on days 0, 4 and 28. Feeding the fishmeal-based control diet increased (P<0.001) ADC for a number of macro- and micro-nutrients, growth rate, feed efficiency, and tissue ash and P concentrations compared with the plant protein-based diet; however, supplementation of the plant protein-based diet with microbial phytase improved (P<0.001) the ADC for energy, protein (P<0.05), ash, P and a number of macro- and micro-nutrients. Fish growth, feed efficiency, concentrations of tissue ash and P, and retention of P (P<0.001) and N (P<0.05) were also increased by supplementation of the plant protein-based diet with microbial phytase; values for these parameters approached those of the fish meal control diet in the final 28 days of the experiment. In the same period, inclusion of microbial phytase resulted in lower (P<0.05) total, solid and dissolved P excretion versus all other treatment groups. There was no effect (P>0.05) of phytase supplementation on proteolytic enzyme activity. Encapsulation of microbial phytase tended (P<0.10) to diminish its ability to liberate P. The data suggest that microbial phytase can effectively increase the apparent digestibility and bioavailability of a range of nutrients from plant protein-based diets for rainbow trout, resulting in increased growth performance and tissue mineralization. Encapsulation of phytase reduces this effect, likely due to hindered interaction between the enzyme and dietary phytate-P.

Dietary protein source or energy levels have no major impact on growth performance, nutrient utilisation or flesh fatty acids composition of market-sized Senegalese sole

A growth trial was conducted to test three isonitrogenous diets (59% crude protein, dry matter basis) for Senegalese sole during the ongrowing stage. A control diet (S-15) based on a commercial diet for sole (15% crude fat, 23 kJ g −1 energy) was compared with a plant protein based diet (S-15PP) with similar energy content. This plant-based diet was supplemented with arginine, threonine, methionine and lysine to reach the levels of the S-15 diet. A low-energy diet, S-8, was formulated with the very same feed ingredients as S-15, but dietary fish oil was reduced (8% crude fat, 21 kJ g − 1 ). Triplicate groups of 20 fish with a mean initial body weight of 180 g were reared at 19 °C and fed the experimental diets using automatic feeders that distributed 4 meals a day, during 8 months. At the end of the experiment all groups reached commercial size (> 300 g). Dietary treatments did not affect mean final body weight. Daily growth index was generally low (0.4–0.5) and feed conversion ratio (FCR, range 2.5–2.9) did not vary significantly between treatments. Fish fed S-8 ingested fewer lipids, but its whole body or tissue lipid was equal to fish fed the S-15 and the S-15PP diets. Sole fed the S-15PP diet showed reduced plasma taurine and increased liver vacuolisation due to excess lipid storage. This diet also induced the highest Hepatosomatic index (HSI) and viscerosomatic index (VSI). Muscle, liver or skin total lipid content did not vary significantly amongst treatments. Whole body lipid content and plasma triglycerides were significantly lower in the S-15PP than in the S-15, and cholesterol showed the same trend. Protein gain (23–27 g/kg/day), whole body protein content (18–19% wet weight) and muscle protein content (19%) were not affected by the dietary treatments. Results indicate that replacement of dietary fish meal by a mixture of plant protein sources did not adversely affect growth, feed or protein utilisation of large-sized sole, but increased vacuolization and necrosis signs in hepatocytes. This could probably be avoided by an addition of taurine in the high PP diets. The cardiovascular protection and health beneficial properties associated with fish consumption can be achieved with sole either fed low-fat diets or plant protein based-diets, as confirmed by the still high levels of n- 3 and DHA registered in the flesh of those fish.

Supplementation effect(s) of organic acids and/or lipid to plant protein-based diets on juvenile yellowtail, Seriola quinqueradiata Temminck et Schlegel 1845, growth and, nitrogen and phosphorus excretion

A feeding experiment was conducted to investigate the effect of organic acids and/or lipid supplementation on growth, utilization and environmental loading of nitrogen (N) and phosphorus (P) in juvenile yellowtail fed fishmeal (FM) and plant protein (PP) diets. Six diets as FM (FM-based), FM+P (FM with inorganic P), FM+L (FM with lipid), PP+CA (PP with citric acid), PP+L+CA (PP with lipid and citric acid) and PP+L+FA (PP with formic acid) were formulated. Yellowtails were fed each of the diets in duplicate groups; once a day, 6 days a week to near satiation at water temperature 19.0–25.0 °C for 16 weeks. Fishmeal with inorganic P gave the best growth while PP+L+FA the lowest. However, growth increased in PP+CA and PP+L+CA. Addition of lipid significantly increased N and P retention resulting in significant reduction in N and P excretion. Citric acid and FA supplementation to PP diets also increased retention of P; hence, its excretion was lowered. Thus, CA, FA and lipid in juvenile yellowtail diets can help to partially replace FM with PP sources and reduce inorganic P use to minimize environmental loading from aquafeeds.

Do plant-based diets for Atlantic cod (Gadus morhua L.) need additions of crystalline lysine or methionine?

Atlantic cod (Gadus morhua), initial weight 15 g, were fed ten experimental diets for 15 weeks. The diets were based on a mixture of plant proteins (PP) and fish meal (FM), where PP constituted 65% of dietary protein. PP mixtures were chosen to reach as low levels of lysine and methionine as possible. The diets were supplemented with increasing amounts of lysine (19.2–31.9 g kg−1 diet) or methionine (9.4–12.3 g kg−1 diet), in a regression design. No growth difference among diet groups was found in the plant-based diets. Increased dietary lysine resulted in decreased liver size, plasma triacylglycerol concentration (TAG) and lipid productive value (LPV). Methionine additions did not result in changed Hepatosomatic index (HSI), LPV or plasma TAG. Feed conversion ratio (FCR) and protein utilization were neither affected by lysine nor methionine. Plasma and muscle concentrations of free lysine and methionine correlated with dietary levels 5-h post feeding. Overall conclusion was that cod maintain growth rates in plant-based diets if dietary protein was high, without additional supplements of crystalline lysine or methionine. Lysine intake significantly influenced lipid metabolism, showing the necessity to add lysine in plant protein-based diets to hinder increased lipid deposition. No such effects were found because of lack of methionine additions.

Supplementation of fishmeal and plant protein-based diets for rainbow trout with a mixture of sodium formate and butyrate

Two experiments were conducted to evaluate the effects of adding an organic acid salt blend (OAB, 10g acid moiety kg−1 of a mixture of sodium formate and butyrate, ratio 2:1) and plant proteins (soybean meal and pea protein concentrate) to diets for rainbow trout (Oncorhynchus mykiss) reared in freshwater. The experiments were designed according to a 2×3 factorial design, where the factors were: two protein sources (fish or plant meals) and three methods of applying OAB to the diets (none, before, or after extrusion). In Exp. 1, duplicate groups of 0.95-kg trout were used to assess the effect of OAB on digestibility of nutrients. The supplementation of OAB before extrusion in the plant protein-based diet significantly reduced the digestibility of dry matter, organic matter, crude fat, and most amino acids. Supplementation of OAB after extrusion reduced the digestibility of crude fat both in the fishmeal and plant protein-based diets. Partly replacing fishmeal with plant proteins reduced the digestibility of dry matter, organic matter, crude fat, phosphorous and several amino acids. In Exp. 2, triplicate groups of 0.23-kg trout were used to evaluate the effect of OAB on growth performance and gut health. Supplementation of OAB in both fishmeal and plant protein-based diets before extrusion significantly increased feed conversion ratio, and middle intestine to body weight ratio. Partly replacing fishmeal with plant proteins significantly increased feed conversion ratio. There was no effect of dietary treatment on morphology in the distal intestine. In conclusion, supplementing diets with a sodium formate and butyrate blend did not improve growth rate or feed utilization of rainbow trout. Replacing 36% fishmeal with a combination of soybean meal and pea protein concentrate negatively influenced the nutrient digestibility and feed conversion ratio, but did not affect the growth rate of rainbow trout.

Age and Diet Affect Gene Expression Profiles in Canine Liver Tissue

BackgroundThe liver plays a central role in nutrient and xenobiotic metabolism, but its functionality declines with age. Senior dogs suffer from many of the chronic hepatic diseases as elderly humans, with age-related alterations in liver function influenced by diet. However, a large-scale molecular analysis of the liver tissue as affected by age and diet has not been reported in dogs.Methodology/Principal FindingsLiver tissue samples were collected from six senior (12-year old) and six young adult (1-year old) female beagles fed an animal protein-based diet (APB) or a plant protein-based diet (PPB) for 12 months. Total RNA in the liver tissue was extracted and hybridized to Affymetrix GeneChip® Canine Genome Arrays. Using a 2.0-fold cutoff and false discovery rate <0.10, our results indicated that expression of 234 genes was altered by age, while 137 genes were differentially expressed by diet. Based on functional classification, genes affected by age and/or diet were involved in cellular development, nutrient metabolism, and signal transduction. In general, gene expression suggested that senior dogs had an increased risk of the progression of liver disease and dysfunction, as observed in aged humans and rodents. In particular for aged liver, genes related to inflammation, oxidative stress, and glycolysis were up-regulated, whereas genes related to regeneration, xenobiotic metabolism, and cholesterol trafficking were down-regulated. Diet-associated changes in gene expression were more common in young adult dogs (33 genes) as compared to senior dogs (3 genes).ConclusionOur results provide molecular insight pertaining to the aged canine liver and its predisposition to disease and abnormalities. Therefore, our data may aid in future research pertaining to age-associated alterations in hepatic function or identification of potential targets for nutritional management as a means to decrease incidence of age-dependent liver dysfunction.

The nutritional background of the host alters the disease course in a fish–myxosporean system

The aim of the present work was to determine if a practical plant protein-based diet containing vegetable oils (VO) as the major lipid source could alter the disease course when challenged with the myxosporean Enteromyxum leei, a wide-spread parasite in the Mediterranean basin causing heavy economic losses. Gilthead sea bream (Sparus aurata) fed for 9 months either a fish oil (FO) diet or a blend of VOs at 66% of replacement (66VO diet) were challenged by exposure to parasite-contaminated water effluent. All fish were periodically and non-lethally sampled to obtain biometrical data and to know their infection status. After 102 days of exposure, fish were euthanized and haematological, biometrical, histological, immunological, glutathione and anti-oxidant data were obtained from tissue, blood and serum samples. Anorexia appeared in both exposed groups, but feed intake reduction was higher in 66VO fish. The signs of disease (lower growth, condition factor, specific growth rate, haematocrit) as well as the disease course were worse in fish from 66VO group, with a higher prevalence and intensity of infection, a higher percentage of fish harbouring the parasite in the entire intestinal tract, and a faster establishment of the parasite. Parasite intensity of infection was negatively correlated with growth parameters and haematocrit in both groups, and with complement, lysozyme and hepatic total glutathione in 66VO fish.

Proline and hydroxyproline metabolism: implications for animal and human nutrition.

Proline plays important roles in protein synthesis and structure, metabolism (particularly the synthesis of arginine, polyamines, and glutamate via pyrroline-5-carboxylate), and nutrition, as well as wound healing, antioxidative reactions, and immune responses. On a per-gram basis, proline plus hydroxyproline are most abundant in collagen and milk proteins, and requirements of proline for whole-body protein synthesis are the greatest among all amino acids. Therefore, physiological needs for proline are particularly high during the life cycle. While most mammals (including humans and pigs) can synthesize proline from arginine and glutamine/glutamate, rates of endogenous synthesis are inadequate for neonates, birds, and fish. Thus, work with young pigs (a widely used animal model for studying infant nutrition) has shown that supplementing 0.0, 0.35, 0.7, 1.05, 1.4, and 2.1% proline to a proline-free chemically defined diet containing 0.48% arginine and 2% glutamate dose dependently improved daily growth rate and feed efficiency while reducing concentrations of urea in plasma. Additionally, maximal growth performance of chickens depended on at least 0.8% proline in the diet. Likewise, dietary supplementation with 0.07, 0.14, and 0.28% hydroxyproline (a metabolite of proline) to a plant protein-based diet enhanced weight gains of salmon. Based on its regulatory roles in cellular biochemistry, proline can be considered as a functional amino acid for mammalian, avian, and aquatic species. Further research is warranted to develop effective strategies of dietary supplementation with proline or hydroxyproline to benefit health, growth, and development of animals and humans.

Feed intake and growth performance of Senegalese sole (Solea senegalensis Kaup, 1858) fed diets with partial replacement of fish meal with plant proteins

To be able to study nutrient requirement and utilization in any species, a diet supporting normal feed intake and growth equally well as a traditional fish meal-based diet is needed. Additionally the formulation of the diet should allow low levels of the nutrient under study. When studying the amino acid metabolism and requirements, one cannot rely on the fish meal-based diets as fish meal are nicely balanced according to requirements. Therefore the current study aimed to develop a plant protein-based diet (with low fish meal inclusion) to be used in the nutritional studies of Senegalese sole juveniles supporting feed intake and growth close to that obtained in a fish meal-based control feed. Two experiments were conducted to evaluate whether Senegalese sole juveniles would accept and utilize diets containing high plant protein inclusion. For testing the acceptance of high plant protein inclusion, two diets were formulated: a reference diet that contained fish meal as the main protein source (450 g kg−1 dry matter) whereas in the test diet, fish meal was substituted by a mixture of plant ingredients (soybean meal, corn and wheat gluten) with l-lysine supplementation. In order to improve the palatability, 50 g kg−1 squid meal was added to both diets. The indispensable amino acids (IAA) profile of the test diet was made similar to the control diet by adding crystalline amino acids. Further, automatic feeders were used to improve the feed intake. Fish (24 g initial body weight) were fed the diets for a period of 4 weeks. As fish accepted both diets equally well, a second study was undertaken to test the growth performance. Fish (6 g initial BW) were fed the diets for a period of 12 weeks. The use of automatic feeders to deliver the feed and the addition of both squid and balancing the indispensable amino acids resulted in growth performance and accretion not differing from the fish meal fed control. It can be concluded that juvenile Senegalese sole are able to grow and utilize high plant-protein diets when both diet composition and feeding regime are adequate for this species.

The effect of plant protein-based diet supplemented with dipeptide or free amino acids on digestive tract morphology and PepT1 and PepT2 expressions in common carp ( Cyprinus carpio L.)

Common carp ( Cyprinus carpio) of average body mass 0.07 ± 0.02 g were fed three formulated diets: wheat gluten protein-based diet supplemented with Lys–Gly dipeptide (PP), wheat gluten protein-based diet supplemented with free lysine and glycine (AA), and a wheat gluten protein-based control diet without lysine supplementation (CON), frozen zooplankton (Z) (restricted diet), and a commercial starter food Aglo Norse (AN). After 4 weeks of experimental feeding, fish fed AN diet showed the highest body mass and length. Significantly lower mass occurred in groups fed PP, AA, CON, and Z. Fish fed CON diet showed the lowest intestinal folds and the highest number of mucous cells. Fish fed PP diet showed a significantly higher number of gastrin/cholecystokinin (CCK) positive cells. The diameter of lipid vacuoles in hepatocyte cytoplasm of fish fed formulated diets (PP, AA and CON) was significantly higher than in fish fed zooplankton (Z) and the commercial diet (AN). Hepatocytes of fish fed AA and CON showed a higher nucleus proliferation rate than in the other experimental groups. The quantitative analysis of the number of proliferating cell nuclear antigen (PCNA) and caspase-3(rabbit polyclonal antibody CPP-32)-positive cells showed that the highest proliferation rate was accompanied by the high apoptosis in the intestine of fish fed AA and CON. After 4 weeks of experimental feeding the highest relative expression of PepT1 gene was observed in fish fed PP diet, while the lowest expression occurred in fish fed CON. Feeding carp plant protein-based diet supplemented with Lys–Gly dipeptide (PP) had a beneficial influence on fish growth and metabolism in the digestive tract as compared to fish fed control diet without lysine supplementation (CON).

Tissue-specific robustness of fatty acid signatures in cultured gilthead sea bream (Sparus aurata L.) fed practical diets with a combined high replacement of fish meal and fish oil1

The present study aimed to determine the tissue-specific robustness of fatty acid (FA) signatures of gilthead sea bream (Sparus aurata L.) by analyzing the changes in lipid class and FA composition of skeletal muscle, brain, liver, and mesenteric adipose tissue. Triplicate groups of fish were fed to visual satiety over a 14-mo production cycle with 2 practical plant protein-based diets formulated with either fish oil or a blend of vegetable oils (66% of fish oil replacement) to contain 53% CP and 21% crude fat on a DM basis. Growth rates (P = 0.22) and tissue lipid class composition were not altered by the dietary treatment (P = 0.34 and 0.52 for neutral lipids and phospholipids, respectively). The FA signatures of neutral lipids reflected the composition of the diet, although the output of principal components analysis revealed a divergent FA profile for liver compared with skeletal muscle, brain, and mesenteric adipose tissue. Because the theoretical EFA needs were met by the 2 diets, the FA composition of phospholipids remained almost unaltered in all tissues. Interestingly, however, the brain showed the greatest robustness and regulatory capacity to preserve the phenotype of fish fed fish oil-based diets. The FA signatures of total lipids are a combinatory result of neutral and polar lipids, and the most relevant fat storage tissues (mesenteric adipose tissue and skeletal muscle) were more easily influenced by dietary FA composition. The present study provides new insights into fish tissue FA composition and reinforces the use of FA signatures as useful criteria in determining whether EFA requirements for a wide range of physiological processes, including those of neural tissues, can be met with practical fish feeds.

Effect of plant-based feed ingredients on osmoregulation in the Atlantic salmon lens

Lenses of adult Atlantic salmon fed with a plant oil and plant protein-based diet (plant diet) were compared to lenses of fish fed a diet based on traditional marine ingredients (marine diet) with respect to biochemical composition and functionality ex vivo. After 12 months of feeding, plant diet-fed fish had smaller lenses with higher water contents and lower concentrations of histidine (His) and N-acetylhistidine (NAH) than fish fed with the marine diet. Cataract development in both dietary groups was minimal and no differences between the groups were observed. Lens fatty acid and lipid class composition differed minimally, although a significant increase in linoleic acid was observed. The lenses were examined for their ability to withstand osmotic disturbances ex vivo. Culture in hypoosmotic and hyperosmotic media led to increase and decrease of lens volume, respectively. Lenses from plant diet-fed fish were less resistant to swelling and shrinking, released less NAH into the culture medium, and accumulated His and NAH at higher rates than lenses from marine diet-fed fish. Culture in hypoosmotic medium resulted in higher cataract scores than in control and hyperosmotic medium. mRNA expression of selected genes, including glutathione peroxidase 4 and SPARC (secreted protein acidic and rich in cysteine), was affected by diet and osmotic treatment. It can be concluded that lenses of farmed Atlantic salmon are affected by the diet composition, both in biochemical composition and physiological functionality in relation to osmoregulation.

Assessment of the health and antioxidant trade-off in gilthead sea bream ( Sparus aurata L.) fed alternative diets with low levels of contaminants

The aim of the present work was to analyze the effect of partial and total replacement of fish oil (FO) by a blend of vegetable oils on the health and antioxidant status of gilthead sea bream ( Sparus aurata L.) fed primarily plant protein-based diets. The study included measurements of feed-borne contaminants, gene expression analyses of detoxifying and antioxidant pathways and measures of antioxidant and innate immune descriptors. Polybrominated diphenyl ethers (PBDEs) were almost undetectable in all diets, and the loading-charges of polychlorinated biphenyls (PCBs), dioxin-like PCBs, organochlorine pesticides (OCs), and polycyclic aromatic hydrocarbons (PAHs) were at trace levels decreasing their concentrations according to the level of FO replacement with vegetable oils (0%, 33%, 66%, and 100%). Hepatic detoxifying pathways were down regulated by FO replacement, and the hepatic transcription of cytochrome P450 1A1 and aryl hydrocarbon receptor 1 was significantly reduced in fish fed the 100% vegetable oil diet. Dietary intervention did not alter the hepatic expression of the recycling glutathione reductase, whereas glutathione peroxidase-1 and phospholipid glutathione peroxidase were either down- or up-regulated by total FO replacement. This suggests that vegetable oils prime the in situ repair of peroxidized phospholipids rather than the increased turnover of membrane phospholipids from the undamaged pool of cytosolic free fatty acids. The hepatic expression of non-enzymatic antioxidants (metallothionein, glucose regulated protein 75) was down regulated in fish fed 66% and 100% vegetable oil diets. Hepatic glutathione levels and total plasma antioxidant capacity were also lowest in fish fed high levels of vegetable oils, but the concurrent increase in the GSH/GSSG ratio was interpreted as an index of reduced oxidative stress. This redox balance agrees with the enhanced respiratory burst of blood leucocytes after phorbol myristate acetate stimulation in fish feed the 100% vegetable oil. Total plasma peroxidases and plasma alternative complement pathway were not affected by dietary treatment, whereas plasma lysozyme was significantly decreased in fish fed the 66% vegetable oil diet. Taken together, the results suggest that the health and the antioxidant status of gilthead sea bream was not damaged by high levels of FO replacement in eco-friendly diets, but both the scavenging and production of reactive oxygen species were modulated in concert by complex and nutritionally mediated readjustments.

Dietary supplementation of lysine and/or methionine on performance, nitrogen retention and excretion in pacu Piaractus mesopotamicus reared in cages

A study was conducted to evaluate the effect of dietary supplementation of lysine and/or methionine on growth performance, nitrogen retention and excretion in pacu juveniles reared in cages. Five diets were prepared; four diets based on plant ingredients containing 23% digestible protein (DP), basal: Lys- and Met-deficient, 23L: basal supplemented with lysine only, 23M: basal supplemented with methionine only, and 23LM: basal supplemented with both amino acids and a protein-bound AAs diet based on fish and soybean meal, containing 30% DP. Survival, specific growth rate, protein efficiency rate and feeding cost were not influenced by the dietary treatments ( P > 0.05). Fish fed basal diet showed the lowest mean of N retention. Fish fed 30DP diet showed the best results of weight gain (WG) and apparent food conversion rate (FCR) among the dietary treatments. On the other hand, WG in the 23LM group and FCR in the 23LM and 23M groups were not significantly different from the group fed 30DP diet, and showed the highest mean of N retention. There was higher N excretion ( P < 0.05) when the fish were fed 30DP and 23L diets than the other dietary treatments. Fish fed plant protein-based diets containing 23% DP supplemented with both amino acids or methionine alone showed satisfactory growth and N retention results when compared with fish fed 30DP diet, with the advantage of lower N emissions into water. The results also evidence the pacu's great potential to be reared in cages.

Digestibility of plant protein-based diets by largemouth bassMicropterus salmoides

Commercial farming of carnivorous fish demands the reduction of environmental impact of feeds; that requires minimal use of dietary animal protein. This study investigated the digestibility of diets formulated exclusively out of plant protein, added feed attractants, by the carnivore largemouth bass, Micropterus salmoides. Juvenile largemouth bass (14.0 ± 1.0 cm) conditioned to accept artificial, dry feed were confined in polypropylene cages and fed ad libitum in three daily meals, seven experimental diets containing varying levels of vegetable and animal protein sources, added of different feed stimulants. After last daily meal, cages were transferred to cylindrical–conical-bottomed, 200-L aquaria, where faeces were collected by sedimentation into refrigerated containers, preserved and later analysed for chemical composition. Soybean meal can be used as partial substitute of animal protein in diets for largemouth bass; the poultry by-product meal shows as a good option as animal protein source in these rations. Control treatment – 50PP : 50AP – yielded best performances; the need for the use of fish meal in the formulation for carnivorous diets is, at least, questionable. Results of the digestibility trials demonstrated the importance of determining the diet digestibility, if precision in the formulation of least-cost feeds for carnivorous fish is the ultimate goal.