Effect of dietary supplementation with Bacillus subtilis on the growth,performance, immune response and antioxidant activities of the shrimp (Litopenaeus vannamei)

The objective of this study was to evaluate the effect of dietary supplementation of a probiotic bacterium, Bacillus subtilis, on the growth, immune response and antioxidant activities of shrimp (Litopenaeus vannamei). Shrimps with an average initial weight of 2.11±0.17 g were randomly assigned to four groups with three replicates. The control group was fed a basal diet, and three treated groups were fed diets supplemented with B. subtilis at doses of 1 × 10⁴, 5 × 10⁴ and 10 × 10⁴ colony‐forming unit (CFU) g^?1 feed respectively. After 40 days of culture, 10 shrimps from each replicate were taken randomly for the determination of immune response and oxidization resistance indices. The results showed that the shrimps fed with B. subtilis at a dose of 1 × 10⁴, 5 × 10⁴ CFU g^?1 feed showed significantly better growth than that of the control diet. The phenoloxidase activities showed a tendency to increase with an increased dose of B. subtilis in diets but there was no significant difference among the three treated groups. In addition, phenoloxidase activities were found to be significantly higher (P<0.05) in the groups treated with B. subtilis than that of the control group. Shrimps treated with 5 × 10⁴ CFU g^?1 feed probiotic bacterium showed the highest lysozyme activity and it was significantly higher (P<0.05) than the other groups. However, there was no significant difference in acid phosphatase and alkaline phosphatase activity across all the groups. The total antioxidant capacity, superoxide dismutase and glutathione peroxidase activities in the probiotic‐treated groups were significantly increased (P<0.05) as compared with the control groups. Both maleic dialdehyde concentration and superoxide anion activities in the probiotic‐treated groups were significantly lower (P<0.05) than those of the control. The probiotic did not affect the nitric oxide synthase and the catalase activity in any of the control and treated groups. These results indicated that the probiotic B. subtilis could significantly promote the growth rate of shrimp by increasing the immune function and antioxidant capacity. The most effective dose of B. subtilis in the diet was 5 × 10⁴ CFU g^?1 feed.     

Effects of dietary Lactobacillus delbrueckii on growth performance,body composition,digestive and absorptive capacity,and gene expression of common carp (Cyprinus carpio Huanghe var)

The present study aimed to investigate the effects of dietary supplementation of Lactobacillus delbrueckii (L. delbrueckii) on growth performance, body composition, intestinal enzyme activities and gene expression of Cyprinus carpio Huanghe var. Fish (mean 1.05 ± 0.03 g in triplicate) were conducted for 8 weeks with five treatments in triplicate. The fish in the control were fed a basal diet, and those in D2, D3, D4 and D5 were fed basal diet containing L. delbrueckii at 1 × 10 CFU/g, 1 × 10 CFU/g, 1 × 10 CFU/g and 1 × 10 CFU/g. The growth performance and the hepatic IGF‐I expression of fish increased significantly as L. delbrueckii level increased from 0 to 1 × 10 CFU/g, but decreased significantly with further increasing L. delbrueckii levels. The whole body protein, lipid contents, intestinal digestive and absorptive enzyme activities were significantly affected by dietary L. delbrueckii levels with the highest values observed in fish fed diet containing 1 × 10⁶ CFU/g L. delbrueckii. The carbohydrate content showed the opposite trend. The results suggest that supplementation of L. delbrueckii as probiotic in the diet at approximately 1 × 10 CFU/g can improve growth performance, intestinal enzyme activities and the growth‐related gene expression in Cyprinus carpio Huanghe var.     

Administration of probiotic Bacillus licheniformis induces growth,immune and antioxidant enzyme activities,gut microbiota assembly and resistance to Vibrio parahaemolyticus in Litopenaeus vannamei

This study aimed to elucidate the effects of dietary Bacillus licheniformis ATCC 11946 (BL) on the growth, immune and antioxidant activities, intestinal morphology and microbiota, and susceptibility to Vibrio parahaemolyticus (VP_AHPND) in juvenile pacific white shrimp, Litopenaeus vannamei (LV). Juvenile LV (initial weight = 0.63 ± 0.001) were fed diets containing varying BL concentrations (0 (BL0), 10⁶ (BL1), 10⁷ (BL2) and 10⁸ (BL3) CFU/g feed) for 8 weeks. Growth performance, immune and antioxidant enzyme activities, and intestinal morphology significantly improved in the probiotic‐treated groups than the untreated. Regardless of the treatment group, the two dominant phyla were Proteobacteria and Bacteroidetes, whereas the two dominant genera were Ruegeria and Vibrio. Increasing inclusion of probiotics in diets led to significant increase in beneficial bacterial genera (Ruegeria, and Pseudoalteromonas) and a significant decrease in some known opportunistic pathogens (Vibrio, Tenacibaculum, Photobacterium, Kangiella and Spongiimonas) with the BL3 group witnessing the best. A 7‐day challenge study with VP_AHPND showed significantly high protection in the probiotic‐treated groups, with the BL3, BL2 and BL1 obtaining 51%, 34% and 22% relative percentage survival, respectively. In conclusion, BL at 10⁸ CFU/g feed should be used to help in shrimp production since it attained the most significant improvement.     

Dietary supplementation with autochthonous Bacillus cereus improves growth performance and survival in tambaqui Colossoma macropomum

The aim of this study was to evaluate the effect of dietary supplementation with the autochthonous probiotic bacteria Bacillus cereus on growth performance, haematological parameters and survival of tambaqui (Colossoma macropomum). Tambaqui fingerlings (0.94 ± 0.02 g) were fed for 120 days the following diets: basal (without probiotic) and three supplemented diets (4.2 × 10⁴, 3.9 × 10⁶ and 3.3 × 10⁸ CFU/g). Growth performance and haematological parameters were evaluated every 30 days. Thereafter, fish were challenged against Aeromonas hydrophila and survival was evaluated. Probiotic B. cereus improved weight and length gains (p < 0.05), and increased neutrophils and thrombocyte counts (p < 0.05) in tambaqui supplemented with 3.9 × 10⁶ CFU/g diet. Challenged fish fed unsupplemented diet presented the lowest survival rate (33.4%) while fish fed diets supplemented at 4.2 × 10⁴, 3.9 × 10⁶ and 3.3 × 10⁸ CFU/g B. cereus had 88.8%, 80.5% and 80.5% relative per cent survival respectively. These results demonstrated that B. cereus supplemented as probiotics to C. macropomum for 120 days improved physiological and haematological responses, leading to enhanced survival in this fish species.     

Probiotic effect of Streptomyces spp. on shrimp (Litopenaeus vannamei) postlarvae challenged with Vibrio parahaemolyticus

The effect of Streptomyces strains RL8 and N7 on the growth, survival and histological structure of the hepatopancreas of Litopenaeus vannamei was determined. Shrimp post‐larvae of 0.02 ± 0.01 g were fed with diets supplemented with Streptomyces spp. RL8 and N7 at 10⁸ CFU g^?1 of feed for 30 days, followed by challenge with Vibrio parahaemolyticus. Toxicity was also assessed by recording the mortality associated with the use of 1‐100 g/L of cell mass and 10⁸‐10¹⁰ CFU/g of feed of these strains in Artemia salina and L. vannamei, respectively. The group treated with Streptomyces sp. RL8 had significantly better weight gain (0.62 ± 0.18 g) and survival rates (84.44 ± 5.7%) after challenge, whereas the one fed with Streptomyces sp. N7 showed significantly higher survival rate (57.77 ± 6.8%) than the control group (0.55 ± 0.20 g and 11.11 ± 9.0%, respectively). The hepatopancreas of Streptomyces‐fed shrimps showed better histological integrity with significantly lower degree of atrophy and necrotic tubules than their unfed counterpart. No toxicity associated with these strains was found. Consequently, they can be excellent probiotic candidates to improve the physiological status and prevent infectious diseases of cultured L. vannamei.     

Dietary supplementation of probiotics and influence on feed efficiency,growth parameters and reproductive performance in female rainbow trout (Oncorhynchus mykiss) broodstock

The aim of this study was to determine the effects of dietary probiotics on reproductive performance, growth, haematological and biochemical parameters of female rainbow trout broodstock. A total of 60 broodstocks with an average initial weight of 2,267.4 ± 54.9 g were divided into four groups and three replicates in raceway ponds. Fish were fed with diets containing 0 (control), 1 × 10⁹ (P1), 2 × 10⁹ (P2) and 4 × 10⁹ (P3) CFU probiotic per kg diet twice a day for 8 weeks before spawning season. Results revealed that higher levels of dietary probiotics (P3) enhanced protein efficiency ratio and decreased feed conversion ratio (p < .05). There were no significant differences in haematological and other growth parameters among different treatments. According to the results, probiotic‐fed treatments had the lowest levels of cholesterol (237.7 ± 4.3 mg/dl) and the highest levels of total protein (11.3 ± 0.3 g/dl) and albumin (6.9 ± 0.3 g/dl), so that differences were found between P3 and control groups in all cases (p < .05). Based on the observations from reproductive parameters, the highest egg diameter, working and relative fecundities, fertilization and hatching rates, eyed eggs survival and alevins survival rates up to the absorption of the yolk sac were observed in P3 treatment (p < .05). Moreover, eyeing, hatching and yolk sac absorbing stages in P3 treatment were earlier than those in other treatments (p < .05). The results of present study demonstrated that probiotic supplementation improved reproductive performance and some growth and biochemical parameters in female rainbow trout broodstock and the best performance was observed in fish fed 4 × 10⁹ CFU probiotic per kg diet. Due to an increase in egg production and egg size in probiotic‐fed treatments, this feed additive can be used as a suitable ingredient to increase high‐quality egg production in rainbow trout breeders.     

Isolation and identification of Vibrio campbellii as a bacterial pathogen for luminous vibriosis of Litopenaeus vannamei

Outbreak of luminescent disease was reported from Litopenaeus vannamei shrimp farms in Zhangpu County, Southern China during May–July 2011. The clinical signs included fluorescent, less food consumption and high mortality. Bacteria were isolated from the infected shrimps. The pathogen, a luminescent bacterium named VH1 was identified as Vibrio campbellii based on MLSA analysis (16S rDNA, rpoD and toxR). The haemolysin (hly) gene specific in V. campbellii was detected in strain VH1. Pathogenicity test using immersion infection confirmed that strain VH1 was virulent to L. vannamei postlarvae and juveniles, and the LC₅₀ value was 1.55 × 10⁶ CFU mL^?1 and 1.7 × 10⁶ CFU mL^?1 respectively.     

Effects of an Enterococcus faecium‐based probiotic on growth performance and health of Pirarucu,Arapaima gigas

Intensive fish farming has resulted in an increased concern for disease outbreaks. Probiotic use is one of the strategies being developed to improve fish health and productivity. Measures of probiotic colonization, growth performance, haematological characteristics and parasite load were used to evaluate the effect of diets supplemented with Enterococcus faecium on growth and health of Arapaima gigas juveniles. A completely randomized design with four treatments (diet with E. faecium at 1 × 10⁶ CFU/g and 1 × 10⁸ CFU/g, control diet and diet with the culture medium MRS) and three replicates was used. Ninety‐six Arapaima juveniles were distributed in 12 cages fed with the specified diet for 68 days. Colonization of the intestinal tract by lactic acid bacteria reduced the total number of heterotrophic bacteria in fish fed with probiotics compared to controls. Fish fed a supplemented diet containing 1 × 10⁸ CFU/g presented higher values of weight gain, survival and fish growth uniformity, and lower values of feed conversion ratio. The prevalence of Trichodina sp. could have affected the survival of fish in the control group. Reduction in parasite load and an increase in haematocrit, the number of erythrocytes, thrombocytes, neutrophils and monocytes were also observed in fish fed the diet containing 1 × 10⁸ CFU/g. Enterococcus faecium presented a probiotic effect in A. gigas juveniles and can be recommended for use at a concentration of 1 × 10⁸ CFU/g to modify the gut microbiota, improve growth performance and haematology and reduce parasitic load.     

Effect of polysaccharides extracts of algae Ulva rigida on growth,antioxidant, immune response and resistance of shrimp,Litopenaeus vannamei against Photobacterium damselae

This study was carried out to investigate the effect of water‐soluble polysaccharides extract of algae Ulva rigida (WPU) as dietary supplement on growth performance, antioxidant enzyme activity, lysozyme and phenoloxidase activity, and resistance of shrimp (Litopenaeus vannamei) subjected to bacterial infection with Photobacterium damselae. Three replicate groups of shrimp (1.0 g) were fed four diets containing four levels, 0 or control, 0.5, 1 and 1.5 g/kg of WPU for 8 weeks over the growth trial. Thereafter, 30 shrimps from each dietary treatment were infected with bacteria P. damselae to evaluate disease resistance of infected shrimp. The results of this study showed that WPU was effective as a growth promoter for L. vannamei. The best growth rate was observed in shrimp fed 1.5 g/kg of WPU diet. Regarding antioxidant defences, the diets supplemented with three levels of WPU stimulated glutathione peroxidase and catalase activates in experimental shrimps. MDA content of L. vannamei‐fed diet containing WPU 1.5 and WPU 1.0 was lower than WPU 0 and WPU 0. 5 diets. Also, lysozyme and phenoloxidase activities of shrimp receiving WPU at 1.0 and 1.5 level were significantly higher than those fed WPU 0 and WPU 0.5 diets. In addition, using WPU extract in all diets decreased mortality in L. vannamei in a dose‐dependent manner after challenge with P. damselae. These results suggest that incorporation of water‐soluble polysaccharides from green algae U. rigida at 1.5 g/kg doses improves growth and antioxidant activity and enhances the immune responses in shrimp L. vannamei.     

Effects of dietary Bacillus pumilus on growth performance,innate immunity and digestive enzymes of giant freshwater prawns (Macrobrachium rosenbergii)

The present study was conducted to investigate the effects of Bacillus pumilus on the growth performance, innate immunity and digestive enzymes of the giant freshwater prawn, Macrobrachium rosenbergii. Prawns (mean weight: 1.81 ± 0.01 g) were fed different levels of B. pumilus at doses of 0, 1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ CFU/g to produce one control group and three experimental groups (G1, G2 and G3), respectively. After a 60‐day experimental feeding period, the results showed that the final weight, weight gain rate (WGR) and specific growth rate (SGR) were significantly higher in experimental groups than in the control (p < 0.05), whereas these improvements did not differ significantly (p > 0.05) among experimental groups. The improvements in phagocytic activity, respiratory burst (RBs) activity and the activity of catalase (CAT), nitric oxide synthase (NOS) and acid phosphatase (ACP) were significantly higher in G2 and G3 than in the control and G1 (p < 0.05). Further, the activity of CAT, NOS and ACP significantly increased with an increase in the dietary level of B. pumilus (p < 0.05). The activity of phenoloxidase (PO) in G3 was significantly higher than that in the control (p < 0.05). The activity of amylase was significantly higher in the groups G2 and G3 than that in the control group. G3 improved the activity of protease compared with the control (p < 0.05). In conclusion, the results of this study indicated that the potential use of B. pumilusat a dose of 1 × 10⁸ CFU/g feed could improve the growth, immunity and digestive enzymes of M. rosenbergii.     

Clostridium butyricum as probiotic for promoting growth performance,feed utilization,gut health and microbiota community of tilapia (Oreochromis niloticus × O. aureus)

The feeding trial was conducted to evaluate the potentials of Clostridium butyricum in the diet of tilapia. Fish (~14 g) were fed with basal diet supplemented with 0 (Control), 0.5 (C‐1), 1 (C‐2), 2 (C‐3), 4 (C‐4) and 8 (C‐5) g/kg commercial probiotic‐containing C. butyricum (1.5 × 10⁸ CFU/g) for 8 weeks. The results showed that weight gain significantly increased, and feed conversion ratio decreased in the C‐2, C‐3 and C‐4 groups (p < .05). The protein retention (except C‐1 group), lipid retention and apparent digestibility coefficient (ADC) of dry matter in probiotic supplementation groups were significantly enhanced, and ADC of protein in the C‐4 group was also improved (p < .05). The supplementation of probiotic significantly increased villus height in anterior intestines and reduced the numbers of intestinal Escherichia coli (p < .05). High‐throughput sequencing showed that top three phyla namely Planctomycetes in all probiotic‐containing groups, Proteobacteria in the C‐1 and C‐2 groups and Chloroflexi in the C‐3 group had higher level than the NC group. The cumulative mortality was reduced by dietary probiotic after challenging with Aeromonas hydrophila (p < .05). In conclusion, C. butyricum can be supplemented at 1–2 g/kg feed for promoting the growth, feed utilization, gut health and microbiota of tilapia.     

Response of Pacific white leg shrimp (Litopenaeus vannamei) on exposure to aflatoxin in feed

A research was accomplished to find the response of Litopenaeus vannamei to different levels of aflatoxin in feed. Two hundred live L. vannamei were collected from a shrimp breeding station located on the south of Tiab, in Hormozgan province. Aflatoxin contaminated diets with 0.18, 96.21, 184.74, 711.35, 977.11 and 1605.61 µg/kg were prepared and shrimps in six experimental groups with three replicates in each group for 28 days were fed with these diets. The results showed that activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) in haemolymph and histological alternation index (HAI) value of hepatopancreas in treatement groups were significantly higher than control group (p < 0.05). Decreased total protein and fat in haemolymph and increased protein in muscle of treatment shrimps were observed compared with the control group (p < 0.05). The HAI value of 977.11 and 1605.61 μg/kg groups were significantly higher than the control and other groups (p < 0.05). Histological study results showed that calculated HAI (more than 100) in these groups as a result of necrosis lesion observed in hepatopancreas. Moderate to severe alteration was recognized in group fed by 711.35 µg/kg aflatoxin. Minor aflatoxin levels (0.18, 96.21 and 184.74 µg/kg) caused inappreciable tissue alteration. This study demonstrated body composition, haemolymph parameters and histology of hepatopancreas were affected in the aflatoxin‐contaminated feed when the concentration was over 955.14 µg/kg.     

Effects of Pediococcus pentosaceus supplementation on growth performance,intestinal microflora and disease resistance of white shrimp,Litopenaeus vannamei

Litopenaeus vannamei is economically important shrimp species in worldwide aquaculture. This study was conducted to assess the effect of different levels of probiotic Pediococcus pentosaceus (PP) on growth performance, feed utilization, digestive enzyme activity, intestinal microflora count and body composition of L. vannamei. Four diets containing different concentrations [0 (PP0), 10⁶ (PPI), 10⁷ (PPII) and 10⁸ (PPIII) CFU/g] of PP were formulated. After 8 weeks feeding trial, the experimental shrimps were challenged with Vibrio anguillarum and noted the surveillance. At the end of the feeding trial, the obtained results revealed a significant increase (p < .05) in final body weight, final length, weight gain (WG), survival rate, protease and amylase activities, lactobacillus sp. and Bacillus sp. intestinal count, total haemocyte counts (THC) and lysozyme activity in PPIII group when compared with the other groups. Similarly, WG, amylase activity, Bacillus sp. count, THC and lysozyme activity were significantly enhanced in case of PPII compared to the control group (p < .05). Interestingly, FCR and Vibrio sp. counts were significantly decreased in case of PPIII group when compared to the other groups (p < .05). Also, significant level of surveillance was noted in the challenging test with V. anguillarum. These results suggested that the P. pentosaceus improved the growth performance, digestive enzyme activity, immunity and tolerance against V. anguillarum of L. vannamei.     

A Comparison between dietary effects of Cuminum cyminum essential oil and Cuminum cyminum essential oil,loaded with iron nanoparticles,on growth performance,immunity and antioxidant indicators of white leg shrimp (Litopenaeus vannamei)

This study evaluates the effect of dietary cumin essential oil's (CEO) and cumin essential oil's loaded iron nanoparticles (CEO‐loaded NPs) on growth performance, haematological parameters and antioxidant status of white leg shrimp. Shrimps with the initial weight of 3.38 ± 0.014 g were allocated into 15 fibreglass tanks (300 L, 60 shrimps per tank) and were fed with five experimental diets containing 0 g/kg CEO (the control diet), 5 g/kg CEO, 10 g/kg CEO, 5 g/kg CEO‐NPs and 10 g/kg CEO‐NPs for 56 days. After 56 days of culture, the shrimps fed with CEO and CEO‐loaded NPs supplemented diets showed a more significant increase in growth performance (p < .05) than in the control diet. Total haemocyte count (THC) value, large‐granule cells (LGC), hyaline cells (HC)%, superoxide dismutase (SOD) and Alkaline phosphatase (AKP) activity were significantly higher (p < .05) in the shrimps fed with CEO and CEO‐loaded NPs supplemented diets than the shrimps fed with the control diet. Glutathione peroxidase (GPX) enzyme activities along with the glucose and cholesterol concentrations significantly decreased in the shrimps fed with the CEO and CEO‐loaded NPs supplemented diets more than those fed with the control diet. The results suggest that the dietary CEO‐loaded NPs can improve the growth performance, the health status and the antioxidant capacity of L. vannamei.     

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.     

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.     

Effects of potential probiotic Bacillus subtilis KADR1 and its subcellular components on immune responses and disease resistance in Labeo rohita

The present study was conducted to determine the effects of Bacillus subtilisKADR1 and its subcellular components on immunity and disease resistance in Labeo rohita against Aeromonas hydrophila infection. Fish were fed diet containing different concentrations of live bacterial cells (DI‐10⁶, DII‐10⁸ and DIII‐10¹⁰ CFU/g) and another group of fish were immunized intraperitoneally with cellular components (WCPs, CWPs and ECPs) of Bacillus subtilisKADR1. After 4 weeks of trial, fish were challenged intraperitoneally with Aeromonas hydrophila cell suspension and survival percentage was recorded. Significantly higher post‐challenge survivability was recorded in fish groups fed 10⁸ CFU/g of KADR1 (80.24%; RPS = 75.76%) or immunized with WCPs (77.77%; RPS = 72.73%), compared with the control (18.51%). Analysis of immunological parameters viz. serum lysozyme, phagocytosis, serum total protein, respiratory burst, serum IgM levels, superoxide dismutase and alternative complement pathway activity reflected significant enhancement (p < .05) of immune response in fish fed 10⁶, 10⁸ and 10¹⁰ CFU/g of live cells, or immunized with cellular components of Bacillus subtilisKADR1, with the highest values were observed DII fed group, followed by the group immunized with WCPs. Our results suggest that dietary administration of Bacillus subtilisKADR1 at 10⁸ CFU/g can effectively enhance the immune responses and disease resistance in Labeo rohita against Aeromonas hydrophila.     

Combined effects of dietary malic acid and Bacillus subtilis on growth,gut microbiota and blood parameters of Nile tilapia (Oreochromis niloticus)

The study investigated effect of dietary supplementation with malic acid, Bacillus subtilis and a mixture of the two (3 × 2 factorial trial) on Nile tilapia (Oreochromis niloticus) health. Treatment groups (T1–T6) were fed diets containing three levels of malic acid (0.0, 5.0 and 10.0 g/kg), each of which was supplemented with 0 and 1.1 × 10⁵ cfu/g B. subtilis, respectively. Each treatment group was assigned randomly to triplicate groups of 35 fish (5.26 ± 0.06 g) in 18 tanks for 84 days. The results indicated that survival was higher in all dietary treatments as compared to the control fed fish. The highest values of FBW, WG and SGR (%), PER, PPV and ER were recorded in groups T4 and T6, which were fed diets supplemented with 5 g malic acid/kg and 1.1 × 10⁵ cfu/g B. subtilis and 10 g malic acid/kg and 1.1 × 10⁵ cfu/g B. subtilis, respectively. The best value of FCR was obtained in groups T4 and T6. The lowest total bacterial count in the gut and faeces was detected in fish from group T6. The values of haematocrit, haemoglobin, red blood cells, white blood cells, total protein, albumin and globulin were significantly higher (p < .05) in fish from groups T4 and T6 (diets supplemented with malic acid and B. subtilis). As compared to the control fed fish, te mixture of these substances are promising as immune enhancher in aquacultured fish.     

Dietary supplementation with Bacillus subtilis LT3‐1 enhance the growth,immunity and disease resistance against Streptococcus agalactiae infection in genetically improved farmed tilapia,Oreochromis niloticus

A feeding trial was conducted to investigate the effect of different levels of Bacillus subtilis LT3‐1 in diets on growth, immune parameters, intestinal morphology and disease resistance in genetically improved farmed tilapia, Oreochromis niloticus. Fish (46.91 ± 0.17 g) were fed with a basal diet supplemented with B. subtilis LT3‐1 at 0 (B0), 3.8 × 10¹⁰ (B1), 7.6 × 10¹⁰ (B2), 1.14 × 10¹¹ (B3) and 1.52 × 10¹¹ (B4) CFU kg^?1 for 6 weeks. The results showed that the weight gain of fish in B1 group was significantly enhanced compared to that in B0 group (p < 0.05). The addition of B. subtilis significantly affected serum biochemical indices (total protein, albumin, aspartate aminotransferase, alkaline phosphatase). Besides, the haematocrit, total counts of red and white blood cells, as well as the serum catalase and lysozyme activities, were increased, whereas the serum malondialdehyde, the serum immunoglobulin M and complement three contents were reduced. Parameters for intestinal morphology suggested a healthier intestine for the fish fed B. subtilis‐supplemented diets than fish fed the control diet. The survival rate after Streptococcus agalactiae challenge increased in tilapia fed with B. subtilis. The present study demonstrated B. subtilis can effectively improve growth, immunological status and resistance against S. agalactiae infection in tilapia farming.     

Effect of dietary lipid level on growth,lipid metabolism and health status of the Pacific white shrimp Litopenaeus vannamei at two salinities

Three isonitrogenous diets containing 60 g kg^–1, 90 g kg^–1 or 120 g kg^–1 lipid were formulated and fed to the Litopenaeus vannamei (2.00 ± 0.08 g) under two salinities (25 or 3 psu) in triplicate for 8 weeks. Shrimp fed 90 g kg^–1 lipid had higher weight gain and specific growth rate than shrimp fed the other two diets regardless of salinity, and the hepatosomatic index increased with increasing dietary lipid at both salinities. The shrimp at 3 psu had significantly lower survival and ash content, higher condition factor, weight gain and specific growth rate than the shrimp at 25 psu. Increasing dietary lipid level induced the accumulation of serum MDA regardless of salinity, and at 3 psu, it reduced the serum GOT and GPT activities and the mRNA expression of TNF‐α in intestine and gill of L. vannamei. The hepatopancreatic triacylglycerol lipase (TGL) and CPT‐1 mRNA expression showed the highest value in shrimp fed 90 g kg^–1 lipid diet at 3 psu. This study indicates that 120 g kg^–1 dietary lipid may negatively affect the growth and induce oxidative damage in shrimp, but can improve immune defence at low salinity; 60 g kg^–1 dietary lipid cannot afford the growth and either has no positive impact on the immunology for L. vannamei at 3 psu.