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.     

Potential of indigenous Bacillus spp. as probiotic feed supplements in an extruded low‐fish‐meal diet for juvenile olive flounder,Paralichthys olivaceus

A 12‐week feeding trial was designed to assess the probiotic potential of indigenous Bacillus amyloliquefaciens and/or Bacillus subtilis singly or in combination with Bacillus licheniformis in an extruded feed for olive flounder (Paralichthys olivaceus) juveniles. A high fish meal (FM) diet (control) and a low‐FM diet containing an alternative protein blend (30% FM replacement, FM30) were formulated. Three other experimental diets were prepared by inclusion of B. amyloliquefaciens (BA), B. subtilis (BS), or a mixture of B. amyloliquefaciens, B. subtilis, and B. licheniformis (BASL) into FM30 diet, with a final concentration of 10⁶ CFU/g diet. Results indicated that the FM30 diet was well tolerated by flounder, and the overall performance was not affected by dietary treatments. Lysozyme activity and total immunoglobulin level were significantly reduced in flounders when fed with the FM30 diet compared with the BASL and BA diets, respectively. The Bacillus additives neither enriched the relative abundance of the corresponding Bacillus spp. in the relevant gut microbiota of olive flounder nor modulated the presumptive gene functions of the gut microbiome. Despite the absence of growth‐promoting effect, the tested probiotics could still be economically viable for use as immunostimulants in commercial flounder diets with partial FM replacement.     

Effects of multienzyme complex and probiotic supplementation on the growth performance,digestive enzyme activity and gut microorganisms composition of snakehead (Channa argus)

The major objective of this study conducted for 7 weeks was to investigate the influence of supplementation with multienzyme complex and probiotic and their interaction effects on the growth performance, body composition, serum biochemical parameters and gut microorganism composition of snakehead (Channa argus). There were four treatments in this experiment coded as control, probiotic (Bacillus amyloliquefaciens), multienzyme (amylase, acid protease and papain) and pro‐multi (B. amyloliquefaciens and amylase, acid protease and papain), respectively. The results demonstrated that snakeheads on the multienzyme resulted in better growth performance in terms of final body weight (FBW), weight gain ratio (WGR) and feed conversion ratio (FCR) significantly (p < 0.05) than those on the control diet, while they did not (p > 0.05) on probiotic and pro‐multi. Snakeheads receiving multienzyme increased significantly (p < 0.05) the serum parameters, including albumin, total protein and AKP and probiotic increased AKP and lysozyme meanwhile decreased the LDL‐C significantly (p < 0.05) compared with control. Analysis of the composition of gut microorganisms showed that four dominant microorganisms were Spirochaetes, Proteobacteria, Firmicutes and Bacteroidetes. Probiotic could enhance the richness and diversity of gut microorganisms in snakeheads, furthermore revealing a means of evaluating the relationship between feed supplementation and microorganisms.     

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.     

Autochthonous probiotic bacteria modulate intestinal microbiota of Pirarucu,Arapaima gigas

This study aimed to investigate the ability of two probiotic strains (Lactococcus lactis subsp. lactis and Enterococcus faecium) to colonize Arapaima gigas intestines and their competence in modulating gut microbiota, morphology, and immunological status. A total of 135 A. gigas (58.86 ± 10.25 g) were divided into three treatments: (a) fish fed a diet containing L. lactis subsp. lactis at 1 × 10⁸ CFU^?1, (b) fish fed a diet containing E. faecium at 1 × 10⁸ CFU^?1, and (c) fish fed a diet nonsupplemented with probiotic. After 21 days, 12 fish per treatment were sampled. Blood and posterior intestine were sampled for further analysis. High‐throughput sequencing results demonstrated that the relative abundance of Cetobacterium genus was high in all treatments. The number of thrombocytes increased in both groups fed the probiotic, and eosinophils were higher in fish fed E. faecium. Serum antimicrobial activity of fish fed L. lactis subsp. lactis was higher when compared with the other two treatments. In conclusion, both strains could populate the intestinal mucosa of A. gigas and could be used as probiotics in pirarucu production as they can influence hematoimmunological parameters and decrease the abundance of pathogenic bacteria in the gut of pirarucu within 21 days of feeding.     

Effects of dietary live or heat‐inactivated autochthonous Bacillus pumilus SE5 on growth performance,immune responses and immune gene expression in grouper Epinephelus coioides

To evaluate the possible dietary application of live and heat‐inactivated probiotic Bacillus pumilus SE5 in grouper Epinephelus coioides, juveniles (14.6 ± 0.2 g) were fed either a basal control diet (without probiotic) or the basal diet supplemented with 1.0 × 10⁸ CFU g^?1 live (T1) and heat‐inactivated B. pumilus SE5 (T2). The heat‐inactivated probiotic significantly improved the final weight, weight gain (WG) and specific growth rate (SGR) at day 60 and significantly decreased the feed conversion ratio (FCR) at day 30 and 60, while the viable probiotic significantly decreased the FCR at day 60 (P < 0.05). Phagocytic activity, serum complement C3 and IgM levels as well as SOD activity elevated significantly in fish fed the heat‐inactivated probiotic for 60 days (P < 0.05). Furthermore, the heat‐inactivated probiotic remarkably up‐regulated expression of TLR2 and pro‐inflammatory cytokines (IL‐8 and IL‐1β) in head kidney (P < 0.05), but the viable probiotic failed to do so. These results indicated that heat‐inactivated B. pumilus SE5 can effectively improve the growth performance and immune responses of E. coioides.     

Effect of Bacillus cereus as a water or feed additive on the gut microbiota and immunological parameters of Nile tilapia

We evaluated the effects of Bacillus cereus, as an additive in water and feed, on the gut microbiota and immunological parameters of Nile tilapia (Oreochromis niloticus) fingerlings. Experiments were performed in tanks and net cages respectively. Experiment 1: Tilapia were housed in tanks for 42 days, and B. cereus was added to the water at 1.0 × 10⁴ cfu mL^?1 (Treatment 1) and 1.0 ×10⁵ cfu mL^?1 (Treatment 2) weekly. For the control, no probiotic was added. Experiment 2: Tilapia were housed in cages for 42 days, and the feed was supplemented with B. cereus at 1.0 × 10⁷ cfu g^?1 (Treatment 1) and 1.0 × 10⁸ cfu g^?1 (Treatment 2) weekly. For the control, no probiotic was added. Each treatment contained three replicates, with 50 male tilapias per replicate. The fish from the probiotic treatments in both tank and cage experiments had significantly higher serum lysozyme and peroxidase activities than the control. In the cage experiment, alkaline phosphatase and total superoxide dismutase activities in tilapia were significantly higher in probiotic treatments compared with the control. The results of polymerase chain reaction‐denaturing gradient gel electrophoresis showed that B. cereus supplementation in the feed and water affected the autochthonous gut bacteria community of tilapia and stimulated various potentially beneficial bacteria. Therefore, B. cereus, as a water or feed additive, could enhance the immune status and affect the gut microbiota of tilapia. Bacillus cereus was more effective as a feed supplement rather than a water additive for enhancing the immune status of tilapia.     

Dietary probiotic supplementation in growth and health of live-bearing ornamental fishes

Bacillus subtilis, a probiont isolated from the intestine of Cirrhinus mrigala (Hamilton), was incorporated in fish feed at four different concentrations (5 × 10⁸, 5 × 10⁷, 5 × 10⁶ and 5 × 10⁵ cells g^?1) and fed to Poecilia reticulata (Peters), Poecilia sphenops (Valenciennes), Xiphophorus helleri (Heckel) and Xiphophorus maculatus (Gunther) for a period of 90 days. The growth parameters, proximate composition of whole body, digestive enzymes and gut microbiology were monitored at regular monthly intervals. The increments in length and weight and the survival were significantly higher (P < 0.05) and the values of food conversions were significantly lower (P < 0.05) in fishes fed the probiotic feeds. The administration of B. subtilis in diet resulted in an increase (P > 0.05) in body ash and protein content and in the specific activity of protease and amylase in the digestive tract of all the fishes. The counts of total heterotrophs, motile aeromonads, presumptive pseudomonads and total coliforms were significantly lower (P < 0.05) in the gut of the probiotic fed fishes. Bacillus subtilis persisted in the fish intestine and in the feed in high numbers during the feeding period. The high survival and low infectivity recorded in the probiotic feed fed fishes when challenged by immersion assay with the pathogenic Aeromonas hydrophila demonstrate that the probiotic strain confers disease resistance in live‐bearing ornamental fishes. A probiotic concentration of 10⁶ to 10⁸ cells g^?1 is adequate for improved growth performance and survival and for healthy gut microenvironment and use of higher concentration of the probiont did not always lead to significantly better results.     

Inclusion of <Emphasis Type="Italic">Pediococcus acidilactici</Emphasis> as probiotic candidate in diets for beluga (<Emphasis Type="Italic">Huso huso</Emphasis>) modifies biochemical parameters and improves immune functions

Administration of probiotic candidates in fish has generally been shown as a useful strategy to improve growth performance, survival, digestive enzyme activity, and gut microbiota. Unfortunately, the sero-immunological responses of different fish to different probiotic candidates are poorly understood. The present study assessed the effect of Pediococcus acidilactici as a probiotic on the biochemical and immunological parameters of beluga. Fish (248.32?±?10.21 g) were fed a control diet (without P. acidilactici( and three different doses of P. acidilactici-supplemented diets (10⁷, 10⁸, and 10⁹ CFUg^?1 diets) for 8 weeks. On week 8, blood and serum were sampled. Dose-dependent increase of immunological parameters (respiratory burst activity, lysozyme content, serum antibacterial activity, and total immunoglobulin) and biochemical parameters (total protein and albumin levels) was observed. However, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly increased in the juvenile beluga fed by 10⁹ CFUg^?1 P. acidilactici-supplemented diet compared to the other groups. Based on the results of this evaluation, it is reasonable to conclude that the inclusion of P. acidilactici as probiotic in diets for juvenile beluga improves the sero-immunological parameters of the fish and should be considered by farmers as a strategy to improve fish health.     

Effects of Isatis root polysaccharide on non‐specific immune responses and nutritive indices in obscure pufferfish,Takifugu obscurus

This study examined the effects of Isatis root polysaccharide (IRPS) on the growth and non‐specific immunological responses of obscure pufferfish (Takifugu obscurus) as well as the potential of using this Traditional Chinese Medicine for disease prevention. The antioxidant capacities, lysozyme and complement C3 activities in phagocytosis, erythrocyte C3b receptor rosette rates, respiratory burst activity, body weight increase (BWI), feed conversion ratio (FCR) and several other nutritive indices were determined in pufferfish fed a control diet or diets containing either a low or high level of IRPS. The results showed that IRPS played a positive role in regulating the leukocyte phagocytic rate, respiratory burst and antioxidant enzymes. The IRPS‐fed fish showed an increased BWI and reduced FCR compared with pufferfish fed the control diet. The significant alterations of non‐specific immune response parameters in fish fed the less IPRS diet were rapid, occurring within 7 days, but were then reduced, whereas those in fish fed the more IRPS diet peaked at 10–15 days of treatment but were maintained for at least 30 days. Isatis root polysaccharide activates host immune function, improves phagocytosis by macrophages and exerts direct antimicrobial and antiviral effects, thereby helping to resist infection.     

Isolation and characterization of Bacillus spp. M001 for potential application in turbot (Scophthalmus maximus L.) against Vibrio anguillarum

The aim of this study was to screen Bacillus strains from the guts of Scophthalmus maximus, Paralichthys olivacues, Epinephelus coioides and Clupanodon punctatus, for use as probiotics in aquaculture. Eight Bacillus strains were screened, and strain M001 was selected for probiotic study based on its antagonistic activity against multiple aquatic bacterial pathogens including Vibrio anguillarum, V. campbellii, V. vulnificus, V. parahamolyticus, Streptococcus sp. and Edwardsiella tarda. M001 was identified as B. amyloliquefaciens based on the biochemical tests and 16S rRNA gene analysis. In vitro experiments revealed that M001 was able to grow at a wider range of temperature, pH and salinity and was capable to use turbot mucus as nutrient for growth. Additionally, M001 isolate greatly inhibited the growth of V. anguillarum by producing antibacterial substances and was acid tolerance, non‐antibiotic resistance and non‐harmful. Thereafter, the potential probiotic effect of M001 was tested in turbot by dietary administration of M001 at a dose of 10⁸ CFU g^?1 diet for 42 days. No significant differences of weight gain, specific growth rate and feed ratio were found in the M001‐diet group of fish compared with control fish, but which increased, respectively, by 5.5%, 4.7% and 7.0% after 42 days of feeding. Several digestive enzyme activities were found to increase significantly in the M001‐diet group, including protease and amylase activities in hepatopancreas, protease activity in intestine and lipase activity in stomach (P < 0.05). Sera superoxide dismutase activity and total protein content (P < 0.05) were also increased significantly (P < 0.05) in the M001‐diet group. The challenge experiment showed that the M001‐diet group of fish showed a relative per cent of survival of 62.7% against V. anguillarim infection. The Bacillus M001 identified from this study has good potential to provide vibriosis control as probiotic feed additive for turbot aquaculture.     

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.     

Immune responses and gut morphology in Senegalese sole (Solea senegalensis) fed dietary probiotic supplementation and following exposure to Photobacterium damselae subsp. piscicida

The aim of this study was to determine the effect of a dietary multi‐species probiotic on growth, gut morphology and immune parameters in Senegalese sole (Solea senegalensis). Fish were fed with two experimental diets, a control diet and the same diet supplemented with the probiotic for 72 days. A sub‐lethal bath challenge with Photobacterium damselae subsp. piscicida was performed after the growth trial. Intestine and blood samples were collected to study gut structure and plasmatic immune parameters. No significant differences were found in growth performance. The analysis of gut morphology showed a significant increase in intestinal villi height of Senegalese sole fed the probiotic. Regarding circulating leucocytes, dietary probiotic supplementation increased thrombocytes levels whereas a decrease in the proportion of lymphocytes was observed. No significant differences were observed in humoural immune parameters. Bath challenge differentially affected leucocyte counts and increased peroxidase activity. This study presents the possibility of using dietary probiotic supplementation to increase Senegalese sole welfare since gut morphology was positively affected. Although the immune response after a bacterial challenge was not modulated by dietary treatment, further studies would be instrumental to unravel eventual dietary benefits on immune mechanisms.     

Haematologic and immunologic parameters of bullfrogs,Lithobates catesbeianus,fed probiotics

The effects of two probiotics (P₁–Lactobacillus acidophilus, Bifidobacterium bifidum and Enterococcus faecium and P₂–Bacillus subtilis) supplemented to commercial feed (40% crude protein) on the haematological and immunological parameters of the bullfrog Lithobates catesbeianus were studied. Two doses of each probiotic (5 and 10 g kg^?1 of food) were added to the diets and fed to frogs, totalling five treatments over 112 days. Haematological analyses consisted of total and differential leucocyte counts, erythrocyte and thrombocyte counts, haematocrit, haemoglobin levels and RBC indices (mean corpuscular volume, mean corpuscular haemoglobin – and mean corpuscular haemoglobin concentration) and the immunological parameters included phagocytic capacity and phagocytic index of peritoneal phagocytes. The results showed that the probiotics did not significantly influence any of the haematological parameters measured. However, immunological assays showed that the probiotics had an immunostimulating effect. The greatest effects were seen with probiotic P₁ fed at a dose of 10 g kg^?1 of diet and probiotic P₂ fed at 5 g kg^?1 of diet.     

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.     

Effect of dietary supplementation of probiotic on performance and intestinal microflora of Chinese soft‐shelled turtle (Trionyx sinensis)

This experiment was conducted to study the effect of dietary supplementation of probiotic on performance and intestinal microflora of Chinese soft‐shelled turtle. Healthy Chinese soft‐shelled turtles (6000 pieces with average weight of 5 g) were selected and randomly divided into two groups: control and treatment with three replicates each. The control was fed on normal basal diet, whereas treatment was fed on basal diet supplemented with 1 × 10⁸ cfu.g^?1 Bacillus subtilis preparation. The results showed that the final mean weight of treatment (265.84 ± 3.48 g) was significantly higher (P < 0.05) than that of control (240.45 ± 4.32 g). There was significant difference (P < 0.05) in FCR, and DGs were obtained in probiotics fed group as compared to control. The level of sucrase, maltase, amylase, lipase and ATPase of treatment was significantly higher (P < 0.05) than that of control. Pyrosequencing showed that the dietary supplementation of probiotic Bacillus strain decreased microbial diversity. Phylum Firmicutes was dominant in both groups. Compared with the control, Firmicutes was increased, while others were decreased in treatment group. The results indicated that dietary supplementation of probiotic can improve growth performance, digestibility and intestinal microflora in Chinese soft‐shelled turtle.     

Probiotic bacteria may prevent haemorrhagic septicaemia by maturing intestinal host defences in Brazilian native surubins

The farming of hybrid surubins in Brazil has been affected by bacterial diseases. To avoid this problem, the development of prophylactics such as probiotics has proved to be a promising tool against bacterial outbreaks. This study evaluated the dietary supplementation with lactic acid bacterium Weissella cibaria and its probiotic action in the intestinal tract focusing the hemato‐immunological parameters, histology and electron microscopy. A total of 96 fish were maintained in a recirculation system and divided into 12 tanks, two treatments (supplemented and unsupplemented fish) and six replicates. Fish were fed supplemented commercial diet with W. cibaria for a period of 45 days, and the unsupplemented fish were with commercial feed without probiotic. The numbers of red blood cells, thrombocytes and lymphocytes were higher in supplemented fish after 45 days (P < 0.05). The percentage of phagocytosis, the agglutination titre and the total immunoglobulin concentration were higher in fish fed probiotic. Fish fed supplemented diet presented increased length and width of the intestinal villi, the number of goblet cells and villi's perimeter. The probiotic W. cibaria was capable of colonizing and benefitting the surubins' gastrointestinal tracts, improving intestinal health and the hemato‐immunological parameters of fish.     

Evaluating the use of Lactobacillus acidophilus as a biocontrol agent against common pathogenic bacteria and the effects on the haematology parameters and histopathology in African catfish Clarias gariepinus juveniles

This study was carried out to evaluate the use of Lactobacillus acidophilus as a biocontrol agent against some common fish pathogenic bacteria (Staphylococcus xylosus, Aeromonas hydrophila gr.2 and Streptococcus agalactiae) in African catfish, Clarias gariepinus. Eight treatments were designed inclusive of 10 C. gariepinus juveniles (mean weight 190 g) per tank, each in triplicate. Four groups of fish were fed a diet supplemented with L. acidophilus, comprising about 3.01 × 10⁷ colony‐forming units per gram of diet (the probiotics diet), while the other four groups were fed a diet not supplemented with probiotics (the non‐probiotics diet). In the first group, fish were injected with 1 mL physiological saline and fed the non‐probiotic diet (non‐probiotic control); in the second, third and fourth groups, fish were injected with 1 mL each of S. xylosus, A. hydrophila gr.2 and S. agalactiae, respectively, and were all fed the non‐probiotic diet (designated as non‐probiotic treatments; NPsx, NPah and NPsa respectively). In the fifth group, fish were injected with 1 mL physiological saline but fed the probiotic diet (probiotic control), while fish in the sixth, seventh and eighth groups were each injected with 1 mL of S. xylosus, A. hydrophila gr.2 and S. agalactiae, respectively, and were all fed the probiotic diet (and designated as probiotic treatments; Psx, Pah and Psa respectively). Blood samples were collected for haematology analysis, while samples of the liver and kidney were examined for pathohistology after 7 and 21 days of infection. The results showed that the haematology parameters, packed cell volume, haemoglobin, erythrocyte sedimentation rate, red blood cell, white blood cell, total serum protein, Mg²⁺, Ca²⁺, Cl^?, glucose, cholesterol and total immunoglobulin concentrations and the pathohistology of the liver and kidney were better in the challenged fish (infected) maintained on the probiotic diet than those in the groups fed the non‐probiotic diet. It is concluded, based on these results, that L. acidophilus is useful as a probiotic agent in C. gariepinus against these pathogenic bacteria (S. xylosus, A. hydrophila gr.2 and S. agalactiae).     

Protective effects of a synbiotic against experimental Saprolegnia parasitica infection in rainbow trout (Oncorhynchus mykiss)

A combination of probiotics and prebiotics as synbiotics allows assessing their synergistic effects. This study evaluated the effects of a synbiotic supplement on growth performance, haematological parameters and resistance to Saprolegnia parasitica in rainbow trout, Oncorhynchus mykiss (Walbaum) fingerlings. Fish fed a dietary synbiotic in three levels of 0.5, 1.0 and 1.5 g kg^?1 thrice a day. The fingerlings were challenged with Saprolegnia parasitica after 60 days post feeding and their mortalities recorded up to 15 days. The fingerlings at all three experimental treatments showed significant (P < 0.05) increases in final mean weights and specific growth rates (SGR). The best feed conversion ratio (FCR), feed conversion efficiency (FCE) and maximum survival rate were also obtained by the fish fed 1.0 g synbiotic kg^?1 diet. Furthermore, supplementation with synbiotic significantly increased blood factors at all treatments. After challenges with Saprolegnia parasitica, the synbiotic‐fed groups showed significantly higher survival rates compared with the control group. These results reveal that a dietary synbiotic of 1.0 g kg^?1 fed for 60 days leads to increased growth performance and survival rate as well as improved feeding efficiency in rainbow trout fingerling, rendering them more resistant against infection by Saprolegnia parasitica.     

Effects of the probiotic, Lactobacillus acidophilus, on the growth performance, haematology parameters and immunoglobulin concentration in African Catfish (Clarias gariepinus, Burchell 1822) fingerling

This experiment was carried out to evaluate the effects of the probiotic, Lactobacillus acidophilus , on the growth performance, haematology parameters and immunoglobulin concentration in African catfish Clarias gariepinus fingerling. Two experimental diets were formulated to contain 35 g kg⁻¹ crude protein and 10 g kg⁻¹ lipids accordingly and fed three times daily for 12 weeks to 25 C. gariepinus fingerlings per fibreglass tank in 12 replicates each. The control diet was prepared with no probiotic supplementation whereas the second diet was prepared supplemented with a probiotic, L. acidophilus , containing about 3.01 × 10⁷ colonies/g of diet. The results show that growth performance [specific growth rate (SGR) and relative growth rate (RGR)], nutrient utilization [protein efficiency ratio (PER) and feed conversion ratio (FCR)] and survival were significantly ( P <0.05) higher in fish maintained on the probiotic-supplemented diet compared with those on the control diet. Haematology parameters (packed cell volume, haemoglobin, erythrocyte sedimentation rate, red blood cell and white blood cell, total serum protein, Ca²⁺, Mg²⁺, Cl⁻, glucose and cholesterol) and total immunoglobulin concentrations were also significantly better in fish fed the probiotic-supplemented diet than in the control. Although the water quality parameters monitored were better in the fish fed the probiotic-supplemented diet than in the control, the parameters were not significantly different ( P >0.05). From the results of this experiment, we conclude that L. acidophilus can be used as a probiotic agent in African catfish culture, to enhance fish health, survival and better feed efficiency and growth performance.