Use of probiotics to enhance growth,stimulate immunity and confer disease resistance to Aeromonas salmonicida in rainbow trout (Oncorhynchus mykiss)

An 8‐week feeding trial was conducted to evaluate the effects of dietary probiotics on growth, non‐specific immune responses and disease resistance in juvenile rainbow trout, Oncorhynchus mykiss. Fish averaging 5.8 ± 0.8 g (mean ± SD) were fed one of the five experimental diets; one control (Cont), and four other diets were prepared by supplementing single probiotics 1 (Bacillus subtilis; SP₁, 0.5%), single probiotics 2 (Bacillus licheniformis; SP₂, 0.5%), multi‐probiotics (B. subtilis + B. licheniformis; MP, 0.5%) and oxytetracycline (OTC) at 5 g OTC kg^?1 diet. After 8 weeks of the feeding trial, weight gain and specific growth rate of fish fed SP₁, SP₂ and OTC diets were significantly higher than those of fish fed Cont diet (P < 0.05). Superoxide dismutase (SOD) and lysozyme activities of fish fed SP₁, SP₂ and MP diets were significantly higher than those of fish fed Cont diet (P < 0.05). There were no significant differences in SOD and lysozyme activities among fish fed SP₁, SP₂, MP and OTC diets. In challenge test with Aeromonas salmonicida for 15 days, fish fed SP₁, SP₂ and MP diets showed significantly higher cumulative survival rate than those of fish fed Cont diet (P < 0.05). However, there were no significant differences in cumulative survival rate among fish fed SP₁, SP₂, MP and OTC diets. Although there was a little advantage in fish fed MP diet in terms of non‐specific immune responses, single or multi‐probiotics are equally effective statistically. These results indicate that single or multi‐probiotics had equal beneficial effects as an antibiotic replacer on growth performance, non‐specific immune responses and disease resistance in juvenile rainbow trout.     

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.     

Effects of alternative dietary oils on immune response,expression of immune‐related genes and disease resistance in juvenile Nile tilapia,Oreochromis niloticus

The expression of immune‐related genes and immune responses to Aeromonas hydrophila were investigated on Oreochromis niloticus (6.07 ± 0.07 g), by feeding them six different diets for 8 weeks to apparent satiation. Diets contained fish oil (60g/kg FO), virgin coconut oil (60g/kg VCO) and corn oil (60g/kg CO) as sole lipids or blends of 30g/kg FO + 30g/kg VCO (3FVCO), 30g/kg FO + 30g/kg CO (3FCO) and 30g/kg VCO + 30g/kg CO (VO). Fish fed 3FCO recorded higher final weight, percentage weight gain (%WG) and specific growth rate (%SGR) but not significantly higher than all other groups. Triglyceride was higher in fish fed 3FCO than 3FVCO and CO (p ? 0.05), whereas total immunoglobulin (TIg) was not significant (p ? 0.05) between groups. Lysozyme activity was significantly higher in fish fed diet CO while groups FO, 3FCO and VCO recorded the least activities (p ? 0.05). Although alternative complement activity (ACH₅₀), complement proteins (C3 and C4), was not influenced, antibody titre production was significantly higher in fish fed diet 3FCO and lower in group CO. mRNA expression of IL‐1β was significantly upregulated in fish fed VO while the expression of C‐type lysozyme and TGF‐β was not significantly influenced across treatments, although group fed FO recorded higher expression levels, respectively. Lower mortalities of fish were recorded in groups fed 3FCO and VO after 14 days postchallenge with A. hydrophila disease indicating the enhancing effects of vegetable oils to boost immune response and resistance to disease. The study concludes that alternative lipid sources with high polyunsaturated fatty acids (PUFAs‐ALA and LA) (CO) and blend of saturated fatty acids (SFA)(VCO) can partially and or exclusively replace FO with an improved effect on tilapia and resistance to A. hydrophila in tilapia.     

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.     

Effects of two dietary probiotics (Bacillus subtilis or licheniformis) with two prebiotics (mannan or fructo oligosaccharide) in Japanese eel,Anguilla japonica

A 12‐week feeding trial was conducted to investigate the effects of two dietary probiotics; Bacillus subtilis KCTC 2217 or Bacillus licheniformis KCCM 11775 with two prebiotics; mannan oligosaccharide (MOS) or fructooligosaccharide (FOS) in Japanese eel. Fish averaging 12.8 ± 0.47 g (mean ± SD) were randomly distributed into five treatments with triplicate tanks. A basal control diet (CON) and four synbiotic diets supplementing B. subtilis + MOS (BSM), B. subtilis + FOS (BSF), B. licheniformis + MOS (BLM), and B. licheniformis + FOS (BLF). Weight gain and specific growth rate of fish fed all synbiotic diets were higher than those of fish fed CON. Immune‐related gene expression of heat shock protein 70 and immunoglobulin M of fish fed BSF and BLM were significantly higher than those of fish fed CON. Fish fed BSF and BLM had significantly higher intestinal villi length than those of fish fed BLF and CON (p < .05). Disease resistance against Aeromonas hydrophila of fish fed all synbiotic diets were significantly higher than those of fish fed CON (p < .05). Therefore, these results indicated that dietary B. subtilis with FOS (BSF) and B. licheniformis with MOS (BLM) could have beneficial effects on intestinal morphology, and immune‐related gene expression in Japanese eel.     

Beneficial effects on growth,haematic indicators,immune status,antioxidant function and gut health in Juvenile Nile tilapia (Oreochromis niloticus) by dietary administration of a multi‐strain probiotic

The present study was conducted to administer a commercial multi‐strain probiotic (MP), Yilibao (Bacillus velezensis:Bacillus cereus:Lactobacillus casei = 2:2:1), in Nile tilapia, Oreochromis niloticus. In terms of aerobic Bacillus spp. counts, we produced five diets containing 0, 0.34, 1.68, 3.36 and 6.72 g/kg of MP dry product (Control, T1, T2, T3, T4). Seven hundred and fifty tilapia juveniles (13.26 ± 0.01 g) distributed into 25 tanks in five replications were fed their diet for eight weeks. Results showed that fish fed T3 and T4 diets displayed significantly higher final body weight and weight gain (p < .05). Further, all MP‐treated fish exhibited remarkably decreased plasma lipid profiles (cholesterol, triglycerides) (p < .05) and fish fed T3 and T4 diets displayed significantly higher plasma myeloperoxidase activity and complement C3 content (p < .05). Additionally, fish fed T3 and T4 diets exhibited significantly promoted total antioxidant capacity, glutathione peroxidase activity, glutathione level and declined malondialdehyde content in the plasma and/or liver (p < .05). Moreover, significantly elevated chymotrypsin activity, villus height and intraepithelial lymphocytes counts were found in fish fed T3 and T4 diets (p < .05). As fish fed T3 and T4 diets surpassed the other treatments in growth, immune–antioxidative status and gut health, the recommended dose for tilapia is 3.36–6.72 g/kg.     

Effect of <Emphasis Type="Italic">Cratoxylum formosum</Emphasis> on innate immune response and disease resistance against <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> in tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

The effect of aqueous extract of Cratoxylum formosum on innate immune response and disease resistance in tilapia Oreochromis niloticus was investigated. The fish were fed diets containing 0% (control), 0.5% (diet 1), 1% (diet 2), and 1.5% (diet 3) of C. formosum aqueous extract for 30 days. At the end of the experimental period, parameters of innate immune response including phagocytosis of blood leukocytes, lysozyme activity in plasma, and respiratory bust activity were examined. Feeding the fish with diet 2 and diet 3 for 20 days enhanced phagocytic activity and for 30 days stimulated lysozyme and respiratory burst activities. Diet 1 increased the phagocytic activity at 30 days, but did not affect the other measured parameters. All parameters were not significantly changed (P > 0.05) in the control group throughout the experiment. Following 30 days of feeding, fish were infected with S. agalactiae. The cumulative mortalities of bacterial-infected tilapia that were fed diet 1, diet 2, and diet 3 were 56, 12, and 10%, respectively, compared with 85% in the control group. These results indicate that the aqueous extract of C. formosum may elevate the innate immune response and enhance disease resistance in tilapia.     

Oral administration of Escherichia coli lipopolysaccharide enhances the immune system of striped catfish,Pangasianodon hypophthalmus (Sauvage)

Lipopolysaccharide (LPS), a component of Gram negative bacteria, was reported as important immunostimulant for fish. In this study, striped catfish were fed diets containing different Escherichia coli LPS concentrations (0%, 0.01% and 0.05%) for 2 weeks and then fed control feed (0% LPS) for 4 weeks. Plasma cortisol and glucose were rather low and did not differ significantly among treatments (P > 0.05). The respiratory burst activity, lysozyme, complement, total of antibody as well as mortality in fish challenged with Edwardsiella ictaluri were recorded every 2 weeks (W2, W4 and W6). The lysozyme activity significantly increased in fish treated with LPS (P < 0.05) in W2, W4 and W6. The highest values of respiratory burst activity were observed at week 4 in fish fed 0.01% LPS. There were significant differences in total of antibody between fish fed LPS (0.01%) and control in W2, W4. The challenge test with Edwardsiella ictaluri showed that fish fed 0.01% LPS had lower cumulative mortality (40%, 33% and 42%) compared with the fish fed 0.05% LPS (50%, 40% and 47%) and control fish (40%, 57% and 53%) in the three difference sampling times respectively. These results suggest that feed supplemented with 0.01% LPS could enhance immunity of striped catfish after 2 weeks of oral administration and fish could be protected against bacterial infection during the following 4 weeks.     

Supplementation of dietary apple cider vinegar as an organic acidifier on the growth performance,digestive enzymes and mucosal immunity of green terror (Andinoacara rivulatus)

The present study was designed to investigate the effects of dietary apple cider vinegar (ACV) on digestive enzyme activity and growth performance as well as immune responses and antibacterial activity of skin mucus in green terror (Andinoacara rivulatus). Fish were fed diets supplemented with 0%, 1%, 2% and 4% of ACV (40.830 ppm acetic acid concentration) for 63 days. The final weight and weight gain values were observed to be significantly higher in fish fed with 2% of ACV compared to the control group (p < .05). ACV inclusion in the diets had significant effects on SGR (%) and FCR values (p > .05). ACV treatment resulted in a significant increase in the intestinal protease, α‐amylase, lipase and alkaline phosphatase activities compared to control (p < .05). The activities of digestive enzymes in fish fed with 2% and 4% of ACV diets were significantly higher than the other groups (p < .05). The total protein content, alternative haemolytic complement, alkaline phosphatase, total immunoglobulins and lysozyme activities of skin mucus increased significantly in fish fed with ACV diets (p < .05). In conclusion, administration of ACV enhanced digestive enzyme activity, growth performance, immune responses and the immune properties of skin mucus, and it can be used as a natural growth promoter and immunostimulant in green terror culture.     

Effects of Bacillus subtilis strains and the prebiotic Previda® on growth,immune parameters and susceptibility to Aeromonas hydrophila infection in Nile tilapia,Oreochromis niloticus

This study was conducted to evaluate the individual and combined effects of long‐term feeding of diets containing two probiotic Bacillus subtilis group strains (Aqua NZ and AP193) and the prebiotic Previda^®, a commercial hemicellulose extract, on growth performance, immune parameters and Aeromonas hydrophila susceptibility of juvenile Nile tilapia, Oreochromis niloticus. Nile tilapia of average weight 7.47 ± 0.11 g were fed diets formulated with the probiotics and/or the prebiotic, or a control diet for 8 weeks and, subsequently, challenged with A. hydrophila by intragastric gavage at a dosage of 3.9 × 10⁷ CFU per fish. Fish attained a mean weight of 59.5 ± 0.99 g at the end of the growth period. Under the conditions of the present trial, none of the diets significantly improved mean per cent weight gain (P = 0.70), thermal growth coefficient (P = 0.88) or feed conversion ratio (P = 0.87) of Nile tilapia. Except for the diet containing the prebiotic Previda^® only (P = 0.17), all other diets resulted in significantly higher fish survival compared to the control (P < 0.05). The combined effect of the prebiotic and probiotic strains emerged as the most important diet with respect to mortality reduction. The mean lysozyme and respiratory burst activities did not show any significant differences between treatments and control (P = 0.14 and 0.32, respectively). Thus, these probiotic strains used in this study have the potential to prevent disease due to A. hydrophila in O. niloticus.     

Effect of autochthonous and commercial probiotic bacteria on growth,persistence, immunity and disease resistance in juvenile and adult Nile tilapia Oreochromis niloticus

Probiotics are gaining worldwide acceptance as means to improve growth and health of fish. However, the type of probiotic, dose, duration and mode of the application, age and size of the fish are among the factors involved in determining the efficacy of the applied probiotic. In this study, two trials were conducted to evaluate the effect of feeding three probiotics on growth, feed conversion (FCR) and gross yield (GY) in juvenile (28.3 g) and adult (93.4 g) tilapia compared to a control probiotic‐free diet (CON). In the first trial, an autochthonous Bacillus subtilis isolated from the gut of cultured tilapia (TPI), a commercial Lactobacillus acidophilus probiotic (COM1) and a combination of both (MIX1) were tested. In the second trial, the same treatments were tested in adults (101.8 g) only with the replacement of COM1 with another commercial probiotic (COM2) consisting of four bacterial species. Results showed that in juveniles, the MIX1 treatment had the highest (P < 0.05) mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), GY and best FCR, followed by the TPI and the COM1 treatments. Growth in adults was not affected by probiotics and was depressed by COM1. In the second trial, the COM2 treatment had the highest (P < 0.05) MWT, DGR, SGR, GY and best FCR, followed by the MIX2 and the TPI treatments. These results indicate the positive effect of the probiotics on growth and the synergetic effect of mixing more than two bacteria. The TPI had the highest gut colonization and retention after 15 days of withdrawing the probiotics followed by the MIX1 and MIX2 treatments. The COM1 and COM2 showed no proliferation. Generally, probiotics improved the immunity with the TPI causing the highest improvement. Tilapia fed with the TPI, MIX1 and MIX2 bacteria, then challenged by injecting the LD₅₀ dose (10^4.86 cfu per fish) of the pathogenic Proteus vulgaris bacterium had a higher relative percentage of survival than the COM1, and COM2 treatments. Results obtained in this study indicate the higher potential of the autochthonous probiotic bacteria and the mixture of bacteria in enhancing growth, immunity and disease resistance in tilapia than the commercial products and a tendency of fish size discrepancy in the response to probiotics.     

Growth parameters,innate immune response and resistance to Listonella (Vibrio) anguillarum of Dicentrarchus labrax fed carvacrol supplemented diets

The research was aimed to assess the effect of dietary carvacrol (0.025% and 0.05%) on sea bass (Dicentrarchus labrax) growth, immune response and resistance to Listonella anguillarum. Fish (69.2 ± 0.22 g) were fed the experimental diets for 9 weeks. Dietary carvacrol did not negatively affect fish survival, growth performance, feed intake and feed conversion ratio (P > 0.05) nor carcass yield and viscerosomatic, hepatosomatic and mesenteric fat index (P > 0.05). Serum and head kidney leucocytes were collected after 1, 4 and 8 weeks of feeding. Carvacrol significantly reduced serum proteins, immunoglobulins and lysozyme activity (P < 0.01) and moderately increased phagocytosis and pinocytosis of head kidney macrophages. The release of reactive oxygen species by leucocytes was reduced in carvacrol‐fed fish, even if significantly (P < 0.05) only in those fed 0.05% carvacrol for 1 week. Dietary carvacrol did not significantly affect the aspecific immune response, although a potential antioxidant activity might be speculated. Moreover, feeding carvacrol provided an appreciable resistance to a challenge with L. anguillarum, when a bacterial dose lower than the Lethal Dose₅₀ was used. Cumulative mortality in fish fed 0.025% carvacrol was significantly lower than that of untreated controls (75% Relative Per cent Survival).     

Effects of dietary probiotic Lactobacillus plantarum and whey protein concentrate on the productive parameters,immunity response and susceptibility of Nile tilapia,Oreochromis niloticus (L.), to Aeromonas sobria infection

Immunostimulatory feed supplements have an increasingly interest in aquaculture management. Generally, an individual supplement was used in fish diets but it is expected that the use of multi‐supplements may show synergistic enhancements in fish performance, health, and immunity. Therefore, the present investigation was carried out to evaluate the use of dietary probiotic Lactobacillus plantarum and whey protein concentrate (WPC) in practical diets for Nile tilapia, Oreochromis niloticus. Hence, probiotic L. plantarum, WPC and their mixture were incorporated into a basal fish diet (300 g/kg crude protein) as follows: T1 = a basal control diet, T2 = a basal diet containing L. plantarum, T3 = a basal diet containing 1.0 g WCP/kg diet and T4, T5 or T6 = basal diets containing probiotic L. plantarum + 1.0, 2.0 or 3.0 g WCP/kg diet, respectively. Fish (15.2 ± 0.6 g) were fed on one of the tested diets up to apparent satiation twice a day for 60 days. After that, fish were intraperitoneally injected with pathogenic bacteria Aeromonas sobria and fish mortality was observed for 10 days postchallenge. Fish growth and feed intake were significantly improved by dietary probiotic L. plantarum (T2) and/or WPC (T3) over the control group (T1), and highest fish performance was observed in T5–T6 fish groups. Similarly, highest values of haematocrit, glucose, total proteins, albumin, and globulin were significantly observed in T5–T6 fish groups. Likewise, fish fed dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) showed antioxidants and immune‐stimulating activities better than the control group. Fish fed the control diet were more susceptible to A. sobria infection showing highest fish mortality (75.0%). Meanwhile, dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) enhanced significantly the fish resistance to A. sobria infection resulting in maximum values of relative percent of fish survival (73.3%–80.0%) in T5–T6 groups. The present investigation recommended the use of probiotic L. plantarum with 2.0 g WPC/kg diet to improve the growth, antioxidant, immunity responses and tolerance of Nile tilapia to A. sobria infection.     

Effects of dietary supplementation of a marine thermotolerant bacterium,Bacillus paralicheniformis SO‐1, on growth performance and immune responses of Nile tilapia,Oreochromis niloticus

This study was carried out to evaluate the effects of dietary supplementation of thermotolerant bacterium on growth and immune responses of Nile tilapia (Oreochromis niloticus). Bacillus paralicheniformis SO‐1 was isolated from marine environments and incorporated into four isonitrogenous (300g/kg crude protein; cp) and isocaloric (18 MJ/kg) diets at four concentrations: 0, 5, 10 and 20 g/kg diet. Each diet was fed to triplicate groups of Nile tilapia (41.5 ± 0.5 g average weight) at a daily rate of 3% of their biomass, three times a day for 50 days. At the end of the feeding trial, the growth rates, feed utilization efficiency (feed conversion ratio, protein efficiency ratio, protein productive value), digestive enzymes (protease, amylase and lipase) activities, immunological response (serum lysozyme activity, phagocytic activity, respiratory burst and superoxide dismutase activity) and the expression of immune‐related genes [interleukin‐1 (IL‐1), interleukin‐4 (IL‐4) and interleukin‐12 (IL‐12)] were determined. Growth rates, digestive enzymes activities and immunological parameters were significantly improved (p < 0.05) with increasing supplemental SO‐1 up to 10 g/kg. However, further increase in bacterial concentration to 20 g/kg lead to significant decline in fish performance and immune response (p < 0.05). The expression of IL‐1, IL‐4 and IL‐12 genes was significantly up‐regulated (p < 0.05) in the liver of Nile tilapia fed SO‐1‐treated diets. This study clearly demonstrated that B. paralicheniformis SO‐1 could be considered as an efficient growth promoter and immune‐stimulating probiotic for farmed Nile tilapia.     

Growth performance,immune response and disease resistance of rainbow trout (Oncorhynchus mykiss) fed Thymus vulgaris essential oils

Efficacy of Thymus vulgaris essential oils was assessed on growth, immune response and disease resistance of rainbow trout (Oncorhynchus mykiss). Fish weighing 10 g were fed with dietary supplemented of the oils at 0.5, 1.0 and 2.0 ml/kg feed for 2 months. Fish fed with the oils at 0.5 ml/kg feed demonstrated a better weight gain and specific growth rate, compared to other treatments (p < .05). Fish fed with 1.0 ml the oils showed the highest up‐regulation of complement component 3 (C3) and (cluster of differentiation 4) (CD4) genes expression (p < .05), while lysozyme gene expression level significantly increased in fish fed with 2.0 ml of the oils. In addition, at the end of the experiment, the expression of C3 and CD4 genes were significantly up‐regulated in fish fed with 1.0 and 2.0 ml of the oils, while IL‐1ß and lysozyme genes expression levels were significantly decreased in fish fed 2.0 ml oils, towards the end of the trial (p < .05). There was a fluctuation in the levels of Alanine aminotransferase, Aspartate aminotransferase and Alkaline phosphatase in all treatments during the experiment. When treated fish were challenged with Aeromonas hydrophila, the highest survival rate was observed in 0.5 ml/kg treatment, followed by 2 and 1 mg/kg treatments. Overall, these findings demonstrated that dietary administration of T. vulgaris oils especially at 0.5 mg/kg feed can be considered as a potential component for enhancing of the growth, immune responses and disease resistance of trout against motile Aeromonas septicemia caused by A. hydrophila.     

Improvement of reproductive indices,lysozyme activity,and disease resistance in live‐bearing ornamental fish,Poecilia latipinna using Artemia supplementation with treated yeast cell,Saccharomyces cerevisiae

In the present study, the effects of Artemia supplemented with 2‐β‐mercapto‐ethanol (β‐ME) treated yeast cell, Saccharomyces cerevisiae, on growth and reproductive performance, lysozyme activity, and disease resistance to Aeromonas hydrophila of freshwater ornamental species, Poecilia latipinna, were investigated. Within 60 days, molly fish were fed with three treatments including commercial food (T1), un‐supplemented Artemia (T2), and Artemia supplemented with β‐ME‐treated yeast cell (at concentration of 4 × 10⁷ CFU/L of water) (T3). After the feeding period, the fish were exposed to 100 μl of a suspension (1.1 × 10⁷ cells/ml) of A. hydrophila (BCCM5/LMG3279) and the cumulative mortality rates were recorded for 12 days. No significant difference was found between survival rate and growth performance of P. latipinna except for weight gain that was higher in fish fed through Artemia supplemented with β‐ME‐treated yeast cell compared to control group. Fecundity rate was significantly improved in fish fed using T3 with the maximum amount of 49.5 ± 2.29 per female (p < 0.05). Besides, lysozyme activity was significantly increased in group 3 (p < 0.05). Moreover, lowest fish mortality was significantly observed in this treatment (p < 0.05). In addition, the number of colonies formed by yeast cell in T3 (634 × 10³ CFU/g intestine) showed significant difference with other treatments (p < 0.05). In sum, Artemia enriched with β‐ME‐treated yeast improved reproductive indices, immune responses, and resistance against A. hydrophila of P. latipinna.     

Effects of dietary Yucca meal on growth,haematology, non‐specific immune responses and disease resistance of juvenile Nile tilapia,Oreochromis niloticus (Linnaeus, 1758)

A 10‐week feeding trial was conducted to determine the effects of dietary yucca meal supplementation on growth, haematology, non‐specific immune responses and disease resistance in juvenile Nile tilapia, Oreochromis niloticus. Six isonitrogenous and isoenergetic experimental diets were formulated to contain 0% (YMS₀), 0.1% (YMS_0.1), 0.3% (YMS_0.3), 0.5% (YMS_0.5), 1% (YMS_1.0) and 2% (YMS_2.0) dietary yucca meal on the dry weight basis. Results of this study showed a higher growth performance for YMS_0.1 group with significant differences with YMS_0.5, YMS_1.0 and YMS_2.0 groups. In addition, whole‐body protein content of fish fed the YMS_0.1 diet was significantly higher as compared to YMS₀. Plasma lysozyme activity significantly increased in YMS_0.1 group comparing to YMS₀ and YMS_0.5 groups. Respiratory burst activity of phagocytic blood cells was significantly enhanced when fish were fed the YMS_0.1 diet. Results also showed that yucca meal supplementation had moderate effects on glutamic oxaloacetic transaminase and cholesterol levels. After the 14‐day challenge test with Aeromonas hydrophila, cumulative survival of fish fed YMS_0.1 diet was significantly higher than that of fish fed diet YMS₀, YMS_1.0 and YMS_2.0. These results suggest that the optimum dietary yucca meal inclusion level in the diet of juvenile Nile tilapia could be between 0.1% and 0.14% (23.9~33.4 mg kg^?1 saponin) as a feed additive to promote growth, enhance the non‐specific immune responses and increase disease resistance.     

Effects of three carbohydrate sources on water quality,water consumption,bacterial count,growth and muscle quality of Nile tilapia (Oreochromis niloticus) in a biofloc system

This study compared the effect of three sources of carbohydrates: sugar, wheat and malt flours, on water quality, water consumption, bacterial load, growth and flesh quality of Nile tilapia. Adults (120.6 ± 0.64 g) were stocked in 1.2‐m³ fibreglass tanks at a rate of 25 fish/m³. Carbohydrates were added to the biofloc tanks at a C:N ratio of 20:1. Water flow in the non‐biofloc control tanks was adjusted to 0.6 L/day. The 105‐day experiment was conducted in triplicates. Results showed that biofloc treatments (BFT) with zero water exchange had significantly higher mean total ammonia, nitrites, nitrates, alkalinity, total suspended solids and lower pH than the control treatment. The sugar BFT had the highest floc volume. Growth parameters and feed conversion ratio did not differ significantly among treatments. However, tilapia in the malt flour and control treatments had close values. Gross fish yield was higher (p < .05) in the control than the BFT treatments. Water consumption/kg tilapia produced in the control was 42 times higher than the BFT groups. Protozoa dominated the biofloc biota, and wheat flour was the best in harbouring higher bacterial populations in the gut. Protein content and ∑n‐3 fatty acids were highest in the wheat flour biofloc, while malt flour biofloc had the highest lipids. The sugar biofloc had the highest n‐3/n‐6 ratio. Tilapia muscles in the malt flour and control treatments had the highest protein and lipid contents respectively. Tilapia muscles in the wheat flour BFT had the highest ∑n‐3 fatty acids and n‐3/n‐6 ratio. It can be concluded that farming tilapia in BFT using malt or wheat flours as carbon sources is more economical in saving great amount of water with minimal discharge of pollutants without affecting tilapia growth or flesh quality.     

Dietary supplementation with biofloc promotes growth,improves immune and antioxidant status,and upregulates NF‐κB/Nrf2 signalling molecules and stress resistance in Rhynchocypris lagowskii Dybowski

Bioflocs are rich in a variety of probiotics and bioactive compounds, which have been documented to promote growth, regulate antioxidant status and enhance the immune system. A 60‐day experiment was conducted to investigate the effects on growth, antioxidant and immune status, NF‐κB/Nrf2 signalling molecules and stress resistance in juvenile Rhynchocypris lagowskii Dybowski fed different dietary biofloc supplementations. Four hundred fifty R. lagowskii were fed five experimental diets containing graded levels of biofloc from 0 to 160 g/kg (referred to as B0, B4, B8, B12 and B16, respectively). The results showed that biofloc supplementation markedly promoted growth performance (weight gain rate, specific growth rate); improved amylase, lipase and protease activity; and enhanced the activities of glutathione peroxidase, catalase, total superoxide dismutase, total antioxidant capacity, lysozyme, complement C3, complement C4 and immunoglobulin M in the gill, hepatopancreas, kidney, gut and serum. The malondialdehyde content was significantly reduced with treatment B12. In addition, the levels of heat shock protein 70, heat shock protein 90, interferon‐γ and insulin‐like growth factor I were substantially increased with treatment B12 compared to those with the control treatment. Furthermore, biofloc assisted in regulating the expression of NF‐κB/Nrf2 signalling molecule genes, including NF‐κB, TNF‐α, IL‐1β, IL‐8, IL‐10, TGF‐β, Nrf2, Keap1, Maf, HO‐1, CAT, GPX, GCLC and CuZn‐SOD. Overall, our results suggest that dietary supplementation with biofloc can promote growth, improve immune and antioxidant status, and enhance NF‐κB/Nrf2 signalling molecule expression and stress resistance in juvenile R. lagowskii. A suitable supplementation level of approximately 120 g/kg biofloc is recommended in the present study.     

Pre‐challenge and post‐challenge haemato‐immunological changes in Oreochromis niloticus (Linnaeus, 1758) fed argan oil against Lactococcus garvieae

The present study investigated the effects of argan oil, obtained from Argania spinosa, on pre‐ and post‐challenge immuno‐haematological and biochemical responses of Nile tilapia, Oreochromis niloticus. For this purpose, the fish were fed diets containing 0, 0.5%, 1% or 2% argan oil for 45 days. Following 45 days of feeding, fish were challenged with Lactococcus garvieae and mortality was recorded for 15 days. During the pre‐challenge period, significantly higher respiratory burst activity, total white blood cell (WBC), serum lysozyme activity and myeloperoxidase activity were determined in the argan oil‐fed groups. The serum glucose and cholesterol levels decreased whilst total protein and albumin did not change in the groups fed with argan oil‐supplemented diets. After challenge with Lactococcus garvieae, the percentage survival (%) was found to be the highest in the 1% and 2% argan oil‐supplemented feeding groups. Also, there was a significant increase in weight gain, specific growth rate and feed conversion ratio in those fish fed argan oil. The results of this study indicated that after the supplementation of fish diets with argan oil, especially at 1% and 2% concentrations, the immunological, haematological and biochemical values remained similar in both the pre‐ and post‐challenge periods and the immune response against L. garvieae in Nile tilapia was modulated.