Immune responses and gut morphology of Senegalese sole (Solea senegalensis,Kaup 1858) fed monospecies and multispecies probiotics

The current study aimed to determine the effects of dietary probiotic supplementation on growth, gut morphology and non‐specific immune parameters in Senegalese sole (Solea senegalensis) juveniles during a 1‐month trial. Fish were fed for 1‐month two diets with 1.0 or 4.6 × 10⁶ CFU kg^?1) of probiotic A (Bacillus sp., Pediococcus sp., Enterococcus sp. and Lactobacillus sp.) and two diets with 3.5 or 8.6 × 10⁵ CFU kg^?1 of probiotic B (Pediococcus acidilactici) and tested against an unsupplemented diet (control). Growth performance, as well as respiratory burst activity, nitric oxide (NO), alternative complement pathway (ACH50), lysozyme and peroxidase activities, was not affected by the dietary treatments. Probiotic supplementation tended to increased growth homogeneity between tanks having diet A₁ the best possible alternative to decrease costs associated to size grading. Villous length and number of goblet cells of the anterior intestine did not vary among treatments. Muscle duodenal layer was significantly thicker in fish fed probiotic A compared to probiotic B, when included at the lowest level (A₂ versus B₂). The current study indicate that the use of the multispecies probiotic at 1.0 × 10⁶ CFU kg^?1 might enhance protection against pathogen outbreak and increase nutrient absorption, whereas at the highest concentration could reduced size dispersion among tanks.     

Histopathological changes in giant freshwater prawn Macrobrachium rosenbergii (de Man 1879) fed with probiotic Bacillus licheniformis upon challenge with Vibrio alginolyticus

The effect of dietary supplementation of probiotic bacterium Bacillus licheniformis on the histopathological changes in Macrobrachium rosenbergii juveniles (4.0 ± 0.02 g) challenged with known pathogenic strain of Vibrio alginolyticus are reported. Two isocaloric basal diets supplemented with probiotic bacteria B. licheniformis (1.0 × 10⁹ cfu/g feed) and other without probiotic supplementation were fed to the M. rosenbergii juveniles for 45 days. The histological observations revealed no significant changes in the hepatopancreas and gut tissues of both the experimental and the control groups which indicate that the present bacterium is a safe candidate probiont for the host. Prawns were challenged with V. alginolyticus after 45 days of feeding with probiotic diet. The histopathological studies of the hepatopancreas revealed that M. rosenbergii fed with probiotic‐supplemented diet showed less changes as compared to the prawns fed with control diet on second and fourth day of post‐experimental challenge with V. alginolyticus. Histopathological observations revealed that the gills of the prawns fed with control diet were severely affected in comparison to the prawns fed with probiotic‐supplemented diet after challenging with V. alginolyticus. Results from this study revealed the improved protection by dietary incorporation of B. licheniformis in reducing the histopathological manifestations due to V. alginolyticus infection in freshwater prawn.     

Commercial Bacillus probiotic supplementation of rainbow trout (Oncorhynchys mykiss) and brown trout (Salmo trutta): growth,immune responses and intestinal morphology

Probiotic administration is associated with the enhancement of host resistance to environmental and nutritional stressors, improving survival and growth rates. This study was carried out to evaluate the effects of dietary supplementation of Bacillus subtilis and Bacillus cereus toyoi on growth performance, innate immune responses and gut morphology of two trout species feeding a commercial diet high in soybean meal. A commercial probiotic (4.2 × 10⁹ CFU g^?1 of additive) was supplemented to the experimental diets at 0% (control), 0.03% (P₁; 6 × 10³ CFU g^?1 of diet) or 0.06% (P₂; 1.5 × 10⁶ CFU g^?1 of diet) and fed to brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) for 9 and 20 weeks respectively. Rainbow trout showed significantly better growth performance than brown trout, regardless of the dietary treatment. No effect of dietary probiotic supplementation was detected on growth performance, body composition or innate immune parameters (plasma lysozyme, alternative complement and peroxidase activities). In both species, after 9 weeks, intestinal lamina propria and submucosa were widened, with increased presence of inflammatory cells, significantly higher in groups fed probiotics. This inflammatory process, with villi and enterocytes noticeably damaged compared with the control group, was more pronounced in brown trout. Under the current trial conditions, the B. subtilis + B. cereus toyoi had no positive impact in either trout species, on the contrary a harmful effect was observed.     

Soy protein concentrate as a protein source for Senegalese sole (Solea senegalensis Kaup 1858) diets: effects on growth and amino acid metabolism of postlarvae

The objective of this work was to evaluate the effect of a dietary amino acid imbalance, originating from the use of a soy protein concentrate (SPC) as the major protein source, on the growth performance and amino acid metabolism of Senegalese sole (Solea senegalensis) postlarvae. Senegalese sole (85.6±24.6 mg wet weight) were fed one of two experimental diets: one based on fish meal (FM) and another based on SPC. Diets were isonitrogenous (around 56% crude protein) and isoenergetic. Diet acceptability was very good and the growth rate was 6.9% day^?1 for sole eating the FM diet and 6.0% day^?1 for sole eating the SPC diet. Mass‐specific ammonia excretion and the activities of selected amino acid metabolic enzymes (ALAT, ASAT and GDH) did not present significant differences between treatments, although this may have been due to the high variability found for these parameters in the SPC treatment. This variability may suggest different capacities of individual fish to adapt to the possible methionine dietary deficiency. The utilization of amino acids as a substrate for lipogenesis does not seem to be affected by the dietary protein source, since NAPDH‐generating enzymes (G6PD and ME) had similar activities in both treatments. Amino acid metabolism in Senegalese sole postlarvae seems to be slightly affected by the dietary protein source. Nevertheless, the changes induced by the SPC diet do not seem to impair growth, at least at the high dietary protein level used in this experiment.     

Cross‐effects of dietary probiotic supplementation and rearing temperature on growth performance,digestive enzyme activities,cumulative mortality and innate immune response in seabass (Dicentrarchus labrax)

Probiotic influence on fish immune response and digestive capacity is extensively discussed in aquaculture. In this experiment, a feeding trial was carried out for 100 days to evaluate the cross‐effects of probiotic supplementation and rearing temperature (17, 20 and 23°C) in juvenile seabass (Dicentrarchus labrax). The experimental diet was supplemented with a commercial probiotic blend (Biomin AquaStar Growout) at 3 g/kg diet (5.23 × 10⁸ CFU/kg diet), and tested against a non‐supplemented diet (control). Growth performance and innate immune responses were analysed at 70 and 100 days of feeding, whereas digestive enzyme activities were determined at 100 days of feeding. At the end of the feeding trial, fish were subjected to a handling stress and cumulative mortality was recorded. Digestive enzyme activities were influenced by temperature, with α‐amylase and lipase activities peaking at the higher temperature (23°C) and trypsin at the lower temperature (17°C). Immune parameters showed a significant temperature versus feeding duration effect, with complement system (ACH50) and peroxidase peaking at 70 and 100 days of feeding, respectively. Poststress cumulative mortality was higher at the lowest temperature (17°C), especially in fish fed the control diet. In conclusion, water temperature was the main variable affecting the studied parameters, whereas the dietary probiotic supplementation had influence on the chymotrypsin activity and survival rate in seabass reared at 17°C.     

Influence of dietary administration of a probiotic strain Shewanella putrefaciens on senegalese sole (Solea senegalensis,Kaup 1858) growth,body composition and resistance to Photobacterium damselae subsp piscicida

Probiotics are currently being supplemented to cultured fish due to their benefits for fish performance. Herein, we tested the health protection and nutritional effects of probiotic Shewanella putrefaciens (Pdp11 strain), both fresh and lyophilized cells, on Senegalese sole (Solea senegalensis) juveniles. Pdp11 was incorporated into fish feed at concentration of 10⁹ cells g^?1, and then provided to juvenile sole for 2 months. Growth rates were significantly higher in fish fed the fresh probiotic compared with fish fed the control diet. Growth of fish receiving lyophilized bacteria was not improved when compared with controls. Body compositions (protein, total lipids and fatty acids profile) were similar for each dietary treatment. At the end of the study, fish were challenged by intraperitoneal inoculation with a pathogenic strain of Photobacterium damselae subsp. piscicida. Relative percentages of survival (RPS) ranged between 25% and 43.8% for fish receiving both probiotic supplemented diets. Both fresh and lyophilized Pdp11 cells conferred protection against P. damselae subsp. piscicida. However, only fresh Pdp11 enhanced Senegal sole performance. These findings should be taken into account for industry purposes in which lyophilized Pdp11 might be easier to manage.     

Effects of dietary supplementation of citrus by‐products fermented with a probiotic microbe on growth performance,innate immunity and disease resistance against Edwardsiella tarda in juvenile olive flounder,Paralichthys olivaceus (Temminck & Schlegel)

Two consecutive studies were conducted to evaluate the dietary supplementation of citrus by‐products (CB) fermented with probiotic bacteria on growth performance, feed utilization, innate immune responses and disease resistance of juvenile olive flounder. In Experiment I, five diets were formulated to contain 0% (control) or 3% four different CB fermented with Bacillus subtilis (BS), Enterococcus faecium (EF), Lactobacillus rhamnosus (LR) and L. plantarum (LP) (designated as CON, CBF‐BS, CBF‐EF, CBF‐LR and CBF‐LP, respectively). During 10 weeks of a feeding trial, growth performance and feed efficiency were not significantly different among all the fish groups. However, fish fed CBF containing diets had significantly higher survivals than the CON group. Disease resistance of fish against Edwardsiella tarda was increased by the fermentation of CB. In Experiment II, we chose the BS as a promising probiotic and formulated five diets to contain 0%, 2%, 4%, 6% and 8% CBF‐BS. Growth performance was not significantly affected by the CBF‐BS supplementation during 6 weeks of a feeding trial. Innate immunity of fish was significantly enhanced by CBF‐BS supplementation. Myeloperoxidase and lysozyme activities were increased in a dose‐dependent manner by dietary CBF‐BS inclusions. In a consecutive challenge test against E. tarda, an increased disease resistance was found by CBF‐BS supplementation. These studies indicate that the fermentation process of CB with probiotic has beneficial effects on innate immunity and thereby increases disease resistance of olive flounder against E. tarda. Bacillus subtilis can be used as a promising probiotic microbe for by‐product fermentation in fish feeds.     

Effects of dietary supplementation with β‐glucan and synbiotics on growth,haemolymph chemistry,and intestinal microbiota and morphology in the Pacific white shrimp

The goal of this study was to investigate the effects of dietary supplementation with β‐glucan and microencapsulated probiotics (Bacillus subtilis or Pediococcus acidilactici) on growth performance, body composition, haemolymph constituents, and intestinal morphology and microbiota of the Pacific white shrimp Litopenaeus vannamei. Four treatment diets [basal diet (C), β‐glucan‐containing diet (β‐glu), β‐glucan plus B. subtilis‐containing diet (β‐glu+Bs), and β‐glucan plus P. acidilactici‐containing diet (β‐glu+Pa)] were fed to L. vannamei for 90 days. Shrimp fed the β‐glu and β‐glu+Pa diets exhibited similar growth performance and body protein content, which were significantly higher than those of shrimp fed the control diet (P < 0.05). No significant differences in haemolymph triglyceride, cholesterol, protein, haemolymph urea nitrogen or chloride were detected among the experimental diets. However, dietary β‐glucan alone increased the haemolymph glucose level and osmolarity (P < 0.05). Synbiotic supplementation had greater effects on intestinal microbiota and morphology than dietary β‐glucan alone. For example, β‐glu+Bs increased the number of intestinal lactic acid bacteria and decreased the number of Vibrio spp. (P < 0.05), and β‐glu+Pa increased the height of intestinal villi.     

Effects of dietary inclusion of various concentrations of Scutellaria baicalensis Georgi extract on growth,body composition,serum chemistry and challenge test of far eastern catfish (Silurus asotus)

Effects of various concentrations of Scutellaria baicalensis (SB) extract in diets on growth, body composition, serum chemistry and disease challenge test of far eastern catfish (Silurus asotus) were determined and compared with a commercially available immune enhancer. Eight experimental diets were prepared in triplicate: control (Con) diet without supplementation of SB and SB‐0.25, SB‐0.5, SB‐1, SB‐2, SB‐3 and SB‐5 diets containing SB at concentrations of 0.25, 0.5, 1, 2, 3 and 5%, respectively. In addition, 0.1% of a commercial immune enhancer product (CP) was also tested. No significant difference in weight gain of fish was found. Feed consumption, feed efficiency ratio and protein retention of fish were not affected by the experimental diets. At the end of the 8‐week feeding trial, 10 externally normal fish from each tank were infected by Vibrio anguillarum or Strepotococcus iniae. Cumulative mortality of fish fed the Con diet was higher than that of fish fed the all other diets in 10 and 25 days after V. anguillarum or S. iniae infection. Results of this study indicated that dietary inclusion of SB extract was effective in improving survival of eastern catfish after V. anguillarum and S. iniae infection, but the various concentrations of SB did not affect fish performance.     

Effect of Lactococcus lactis and Enterococcus faecium on growth performance,digestive enzymes and immune response of grouper Epinephelus coioides

The effect of dietary administration of Lactococcus lactis MM1 and Enterococcus faecium MM4, two strains of lactic acid bacteria isolated from the gut of juvenile grouper Epinephelus coioides, on the growth, feed utilization, digestive enzymes and immune response of juvenile E. coioides was evaluated. The fish were fed for 60 days with three different diets: control diet (without probiotic), diet P1 supplemented with 1.0 × 10⁸ CFU g^?1L. lactis or diet P2 with 1.0 × 10⁸ CFU g^?1E. faecium. Although growth and feed intake decreased slightly, significant improvement of feed utilization was observed in fish fed diet P1 and diet P2 for 60 days. The hepatopancreatic protease activities in the two probiotic treatments were significantly higher than that in the control. The phagocytic activity, serum superoxide dismutase activity and complement component 4 (C4) and IgM levels were not significantly affected by diet P1 and diet P2. Serum complement component 3 (C3) levels in the two treatments were significantly higher than that in the control. Significant increased serum lysozyme activity was observed in fish fed the diet P1, while significant decreased lysozyme activity was observed in fish fed the diet P2 compared with the fish fed the control diet. There was a significant interaction effect between diet and administration date for the complement C4. The study demonstrates potential for L. lactis MM1 and E. faecium MM4 to improve the feed utilization and modulate the immune function in E. coioides.     

Effect of a Dietary Mixture of Beneficial Bacteria on Growth Performance,Health Condition,Chemical Composition,and Water Quality of Nile Tilapia,Oreochromis niloticus Fingerlings

ABSTRACT

Effects of dietary supplementation of Bifidobacterium longhum, Bifidobacterium thermophilum, Bacillus subtilis, and Lactobacillus acidophilus on growth performance, health condition, body chemical composition, and water quality of Nile tilapia (Oreochromis niloticus) fingerlings were evaluated. Five experimental treatments in triplicate were fed a diet containing 30% crude protein supplemented with variable inclusion of bacterial mixture: control, T1, T2, T3, and T4 containing 0, 1.0, 2.0, 3.0, and 4.0 g bacterial mixture/kg diet, respectively. Fish fed the T4 diet had the highest final body weight, weight gain, specific growth rate, thermal growth coefficient, feed intake, and the best feed conversion ratio. No significant differences in body chemical composition of fish were observed in terms of dry matter, crude protein, lipid, ash, and energy content among all treatments. Probiotic supplementation showed no noticeable differences on haematological and biochemical blood parameters, except for packed cell volume, albumin, albumin/globulin ratio, aspartate transaminase, glucose, uric acid, triglycerides, and cholesterol. Conclusively, Nile tilapia fingerlings diet supplemented with evaluated probiotic with an optimal dietary supplementation of 4 g/kg diet improved growth performance and fish health without a negative impact on water quality. This supplementation could therefore be used as a probiotic in Nile tilapia fingerlings diet.     

Autochthonous probiotic Lactobacillus sp. in the diet of bullfrog tadpoles Lithobates catesbeianus improves weight gain,feed conversion and gut microbiota

Dietary supplementation with probiotics in animal production is an alternative to antibiotics. In frog culture, studies involving native strains of probiotic bacteria and their effects on the performance and intestinal histology of farmed animals are scarce. Therefore, this study aimed to evaluate a diet supplemented with Lactobacillus sp. in tadpoles of Lithobates catesbeianus. This randomized test was performed with two dietary treatments: non‐supplemented control diet and diet supplemented with Lactobacillus sp., with nine replications. The growth performance of Lactobacillus sp., including its bacterial enzymatic activity and stability in feed, as well as colonization and histology of the intestinal tract, was evaluated after 42 days of experimentation. Animals fed with a supplemented diet showed higher weight gain and concentration of lactic acid bacteria in the gut and lower feed conversion. No significant difference was observed in survival, total heterotrophic bacterial count or histological change in the gut between the two treatments. The Lactobacillus sp. strain was able to colonize the intestinal tract and feed and remain at a high concentration of 10⁷ and 10⁶ CFU g^?1, respectively. It produced several enzymes, which might have contributed to the greater weight gain and lower feed conversion in the supplemented animals, thus demonstrating its probiotic potential for use as a dietary supplement in bullfrog tadpoles.     

Effect of dietary administration of Psychrobacter sp. on the growth,feed utilization,digestive enzymes and immune responses of grouper Epinephelus coioides

A 60‐day feeding trial was conducted to assess the effect of incorporating dietary Psychrobacter sp., one predominant bacterium with antagonistic activity in the gut of fast‐growing grouper Epinephelus coioides, on the growth, feed utilization, digestive enzymes and immune responses of E. coioides at regular monthly intervals. The fish were fed with control diet (without probiont) or probiotic diet supplemented with 1.0 × 10⁸ CFU g^?1Psychrobacter sp. No significant improvement in weight gain (WG) and specific growth ratio (SGR) were observed in the probiotic group, but a significant improvement in feed conversion ratio (FCR) was observed in fish fed the probiotic diet for 60 days. Although not statistically significant, enhanced hepatopancreatic protease and lipase activities and intestinal amylase activity were observed in probiotic group at day 60. A slightly increase in phagocytic activity and phagocytic index was observed in fish fed probiotic diet for 60 days. Serum lysozyme activity showed no significant differences between the probiotic group and the control group during the whole experiment period, while an increasing trend of superoxide dismutase (SOD) activity in the probiotic group was observed. Serum complement component 3 (C3) level of the probiotic group was higher than that of control in the whole feeding period, while complement component 4 (C4) level of the probiotic group was significantly higher than that of the control at day 60. The results of the current study firstly demonstrated potential for Psychrobacter sp. as a novel probiont to improve feed utilization, digestive enzymes and innate immunity in E. coioides.     

Effects of dietary supplementation of glycyrrhizic acid on growth performance,survival, innate immune response and parasite resistance in juvenile large yellow croaker,Larimichthys crocea (Richardson)

An 8‐week feeding experiment was conducted to investigate the effects of dietary glycyrrhizic acid (GA) on growth, survival and immune response of juvenile large yellow croaker, in seawater floating net cages. GA was supplemented into the basal diet to formulate four isonitrogenous and isoenergetic practical diets containing 0.00% (the control diet), 0.01%, 0.02% and 0.04% GA of dry weight, respectively. Triplicate groups of 60 fish were fed to apparent satiation by hand twice daily. The results showed that the specific growth rate, survival rate and feed efficiency ratio revealed no significant differences among dietary treatments (P > 0.05). The phagocytic index of head kidney macrophage was significantly increased by the supplementation of 0.04% dietary GA compared to the control group (P < 0.05). Fish fed 0.04% dietary GA also showed significantly higher serum lysozyme activity than fish fed the control diet and diet with 0.01% GA (P < 0.05). The cumulative mortality rate after natural infestation of parasites (protozoan, Cryptocaryon irritans Brown) showed no significant differences among dietary treatments. These results suggested that dietary glycyrrhizic acid improved certain non‐specific immunological parameters of juvenile large yellow croaker. However, GA was not able to protect juvenile large yellow croaker effectively from protozoan infection.     

Effects of dietary soy isoflavones on growth,antioxidant status,immune response and resistance of juvenile grass carp (Ctenopharyngodon idella) to Aeromonas hydrophila challenge

The current study was conducted to evaluate the effect of dietary soy isoflavones (SI) on growth performance, antioxidant status, immune response and resistance to Aeromonas hydrophila in juvenile grass carp (Ctenopharyngodon idella). Six diets were formulated to contain 0 (control), 10, 50, 100, 500 or 1,000 mg SI per kg feed. Each diet was randomly allotted to triplicate net cages, and each net cage was stocked with 30 fish. The fish were fed one of the experimental diets to satiation twice per day for 60 days. The results showed that the WGR and DGC of the 500 mg/kg SI‐supplemented group were significantly higher than those of the non‐SI‐supplemented group (p < .05). Serum LZM and IgM activities in the SI‐supplemented groups were improved compared to the control group. SOD and GSH‐Px levels of fish fed the diet containing 500 mg/kg SI were significantly enhanced compared to those of fish fed the control diet (p < .05). Additionally, serum CAT, GSH‐Px and AKP activities in 50, 100 and 500 mg/kg SI‐supplemented groups were significantly higher than that in the control group (p < .05). The expression of most immune‐related genes (including IFN‐γ2, TNF‐α, M‐CSF2, IL‐6, IL‐12p40 and IL‐4) was significantly affected by dietary supplementation of SI. The group fed with 500 mg/kg SI had the highest 7‐day cumulative survival rate after challenge test (p < .05). The current results revealed that dietary inclusion of SI could improve the immune response and resistance against A. hydrophila and the supplementation level is suggested to be 500 mg/kg diet.     

Effects of cholesterol on growth,feed utilization,body composition and immune parameters in juvenile oriental river prawn,Macrobrachium nipponense (De Haan)

An 8‐week feeding trial was conducted to investigate the effects of dietary cholesterol levels on growth, feed utilization, body composition and immune parameters in juvenile oriental river prawn, Macrobrachium nipponense. Six isolipid (80 g kg^?1 crude lipid) and isoproteic (400 g kg^?1 crude protein) diets, supplemented with 0, 3.0, 6.0, 9.0, 12.0 and 15.0 g kg^?1 cholesterol, were evaluated. Growth performance and feed utilization of M. nipponense were improved as dietary cholesterol levels increased. Weight gain and specific growth rate were highest, and feed conversation ratio was lowest, when prawns were fed a diet supplemented with 9.0 g kg^?1 cholesterol. However, final body weights and survival rates of juvenile M. nipponense were not affected significantly by dietary cholesterol. Body composition of prawns, including moisture, crude protein and crude lipid, was not significantly affected by changes in dietary cholesterol. The immune parameters measured in hepatopancreas, including total antioxidant capacity, and glutathione, catalase, alkaline phosphatase and acid phosphatase activities, were at optimum levels in prawns fed with 9.0 g kg^?1 dietary cholesterol. In summary, the best growth performance, lowest feed conversation ratio, and the most enhanced antioxidant capacity and immunity parameters were attained in juvenile M. nipponense when fed a diet supplemented with 9.0 g kg^?1 cholesterol.     

Dietary supplementation of autolysed yeast enhances growth,liver functionality and intestinal morphology in African catfish

A feeding trial was conducted to evaluate the potential of dietary supplementation of autolysed brewer's yeast (AY) on African catfish. The catfish (22.5 ± 1.15 g/fish, 20 fish 33 L/tank) were fed with either of diets (390 g/kg crude protein, 140 g/kg lipid) supplemented with 0, 3, 6 or 10 g/kg AY (n = 3). After 49 days of feeding, the final body weight and metabolic growth rate of the catfish fed 3 g/kg AY (3‐AY) diet were higher than those fed the control diet (p < .05). The lowest level (p < .05) of alanine transaminase was detected in the blood of the catfish fed 3‐AY diet. The mid‐intestinal histology of the catfish revealed no significant difference (p > .05) in intestinal perimeter ratio. However, an elevated (p < .05) abundance of goblet cells and intraepithelial leucocytes were found in the intestine of catfish fed 3, 6 and 10 g/kg AY diets, with the highest level of abundance recorded in the mid‐intestine of the catfish fed 3‐AY diet. The results suggest that dietary 3 g/kg autolysed brewer's yeast supplementation improves growth performance of African catfish without deleterious effect on liver functionality and gut morphology.     

The effect of dietary methionine on growth,antioxidant capacity,innate immune response and disease resistance of juvenile yellow catfish (Pelteobagrus fulvidraco)

An 11‐week feeding trial was conducted to evaluate the effect of dietary methionine on the growth, antioxidant status, innate immune response and disease resistance to Aeromonas hydrophila of juvenile yellow catfish. Six isonitrogenous and isolipidic practical diets were formulated to contain different graded methionine levels ranging from 6.1 to 16.4 g kg^?1 of dry weight. The results indicated that growth performance and feed utilization were significantly influenced by the dietary methionine levels; fish fed the diet containing 6.1 g kg^?1 methionine level had lower specific growth rate, percentage weight gain (PWG), feed efficiency and protein efficiency ratio than those fed the other diets (P < 0.05). Fish fed the diet containing 16.4 g kg^?1 methionine level had lowest protein contents in whole body and muscle among all treatments. Triacylglycerols, cholesterol, aspartate aminotransferase, alanine aminotransferase and haemoglobin (Hb) in plasma or whole blood were significantly affected by dietary methionine levels. Fish fed the diet containing 6.1 g kg^?1 methionine level had higher superoxide dismutase, glutathione peroxidase activities and malondialdehyde values than those fed other diets. Fish fed diets containing 9.7 and 11.8 g kg^?1 methionine levels had higher lysozyme activity, total immune globulin, phagocytic activity and respiratory burst than those fed other diets. The lowest survival after A. hydrophila challenge was observed in fish fed a diet containing 6.1 g kg^?1 methionine. Quadratic regression analysis of PWG against dietary methionine levels indicated that the optimal dietary methionine requirement for the maximum growth of juvenile yellow catfish was estimated to be 11.5 g kg^?1 of the diet in the presence of 4.0 g kg^?1 cystine (corresponding to 23.5 g kg^?1 of dietary protein on a dry weight basis).     

Dietary nucleotide‐rich yeast supplementation improves growth,innate immunity and intestinal morphology of Pacific white shrimp (Litopenaeus vannamei)

An 8‐week feeding trial was conducted to evaluate the effects of dietary nucleotide (NT)‐rich yeast supplementation on growth, innate immunity and intestinal morphology in Pacific white shrimp (Litopenaeus vannamei). Four isonitrogenous and isolipidic practical diets were formulated to contain 0 (control), 10, 30 and 50 g/kg of NT‐rich yeast, respectively. A total of 480 shrimp with an average initial body weight of 1.86 ± 0.02 g were randomly allocated into four groups, with four replicates per group and 30 shrimp each replicate. The results indicated that shrimp fed the diet containing 50 g/kg NT‐rich yeast had significantly higher weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) than those fed the control diet, and the lowest feed conversion ratio (FCR) was observed in the shrimp fed the 50 g/kg NT‐rich yeast supplemental diet. However, there was no significant difference in survival among all treatments. The crude protein of whole shrimp in the 50 g/kg NT‐rich yeast group was higher than that in the control group. Total protein, triglyceride concentrations, the activities of aspartate aminotransferase and alanine aminotransferase in serum were significantly influenced by the dietary NT‐rich yeast supplementation. The activities of serum phenoloxidase (PO) and lysozyme (LZM) of shrimp fed the diet containing 50 g/kg NT‐rich yeast were higher than those in shrimp fed the other diets. Relative expressions of alp and lzm significantly upregulated in the 30 g/kg NT‐rich yeast group compared to the control group. The intestinal fold height and fold width in the 30 g/kg NT‐rich yeast group were significantly higher than those fed the control diet; and the highest microvillus height occurred in the shrimp fed the 50 g/kg NT‐rich yeast diet. In summary, dietary 30–50 g/kg NT‐rich yeast supplementation promotes growth performance, enhances innate immunity and improves intestinal morphology of Litopenaeus vannamei.     

Dietary indispensable amino acids profile affects protein utilization and growth of Senegalese sole larvae

In diet formulation for fish, it is critical to assure that all the indispensable amino acids (IAA) are available in the right quantities and ratios. This will allow minimizing dietary AA imbalances that will result in unavoidable AA losses for energy dissipation rather than for protein synthesis and growth. The supplementation with crystalline amino acids (CAA) is a possible solution to correct the dietary amino acid (AA) profile that has shown positive results for larvae of some fish species. This study tested the effect of supplementing a practical microdiet with encapsulated CAA as to balance the dietary IAA profile and to improve the capacity of Senegalese sole larvae to utilize AA and maximize growth potential. Larvae were reared at 19 °C under a co-feeding regime from mouth opening. Two microdiets were formulated and processed as to have as much as possible the same ingredients and proximate composition. The control diet (CTRL) formulation was based on commonly used protein sources. A balanced diet (BAL) was formulated as to meet the ideal IAA profile defined for Senegalese sole: the dietary AA profile was corrected by replacing 4 % of encapsulated protein hydrolysate by CAA. The in vivo method of controlled tube-feeding was used to assess the effect on the larvae capacity to utilize protein, during key developmental stages. Growth was monitored until 51 DAH. The supplementation of microdiets with CAA in order to balance the dietary AA had a positive short-term effect on the Senegalese sole larvae capacity to retain protein. However, that did not translate into increased growth. On the contrary, larvae fed a more imbalanced (CTRL group) diet attained a better performance. Further studies are needed to ascertain whether this was due to an effect on the voluntary feed intake as a compensatory response to the dietary IAA imbalance in the CTRL diet or due to the higher content of tryptophan in the BAL diet.