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.     

Diet supplemented with probiotic for Nile tilapia in polyculture system with marine shrimp

The aim of this study was to assess the effect of a probiotic (Lactobacillus plantarum) supplemented diet on Nile tilapia (Oreochromis niloticus) in a polyculture system with marine shrimp (Litopenaeus vannamei) as regards culture performance, hematology, and gut bacterial microbiota. Ten 20-m2 pens were arranged in one earthen pond and stocked with 2 fish (41.9 g) m⁻² and 10 shrimp (2.3 g) m⁻², in total of 40 Nile tilapias and 200 shrimp per experimental unit. Tilapia groups in five of the experimental units were fed a commercial diet supplemented with L. plantarum and the other five with an unsupplemented commercial diet (control). After 12 weeks of culture, the tilapia groups fed the probiotic-supplemented diet presented values 13.6, 7.5, and 7.1% higher for feed efficiency, yield, and final weight, respectively. Viable culturable heterotrophic bacteria counts were reduced, and the number of lactic acid bacteria was increased in the gut of fish and shrimp fed the probiotic-supplemented diet. Hematological analyses showed higher number of thrombocytes and leukocytes in tilapia fed the supplemented diet. L. plantarum utilized in this study colonized the gut of tilapia and shrimp and resulted in reduced number of total bacteria and increased tilapia final weight and feed efficiency.     

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.     

Experimental early pathogenesis of Streptococcus agalactiae infection in red tilapia Oreochromis spp.

Streptococcus agalactiae causes a severe systemic disease in fish, and the routes of entry are still ill‐defined. To address this issue, two groups of 33 red tilapia Oreochromis spp. each of 10 g were orally infected with S. agalactiae (n = 30), and by immersion (n = 30), six individuals were control‐uninfected fish. Three tilapias were killed at each time point from 30 min to 96 h post‐inoculation (pi); controls were killed at 96 h. Samples from most tissues were examined by haematoxylin–eosin (H&E), indirect immunoperoxidase (IPI) and periodic acid‐Schiff; only intestine from fish infected by gavage was evaluated by transmission electron microscopy. The results of both experiments suggest that the main entry site of S. agalactiae in tilapia is the gastrointestinal epithelium; mucus seems to play an important defensive role, and environmental conditions may be an important predisposing factor for the infection.     

Comparison between the intestinal microbiome of healthy fish and fish experimentally infected with Streptococcus agalactiae

Nile tilapia (Oreochromis niloticus) farming is an economic activity that is soaring in the whole world. Septicemia due to Streptococcus agalactiae is the main disease impacting fish farming. The aim of this study was to compare the gut microbiome of healthy animals and animals experimentally infected with S. agalactiae strain 21171A. The microbiome was established with 16S ribosomal DNA next‐generation sequencing (NGS). One hundred Nile tilapias, with an average weight of 35 g, were distributed into two groups. Fifty fish from the challenged group were orally inoculated with 100 μl of a bacterial solution containing 1.98 × 10³ CFU/ml of S. agalactiae strain 21171A, while 50 controls were orally inoculated with sterile saline. After the experiment, 24 fish from the challenged group and 27 fish from the control group were analysed. For both groups, bacteria attached to the mucosa (M) and present in faeces (F) were analysed. The mean of the number of taxa identified in the infected group (M + F) (45.87 ± 30.13) was lower than in the control (M + F) (67.70 ± 21.10) (p < .01). Nineteen bacterial taxa were more abundant in faecal samples from the infected group when compared with the control group (p < .01). Thirty‐nine taxa were associated with mucosa samples from the challenged group when compared to the control samples (p < .01). No OTU was associated with healthy samples. The results demonstrate that the infection with S. agalactiae reduces the variability of the gut microbiota. Moreover, some bacteria proliferate during the infection.     

Effects of a dietary organic acids blend and oxytetracycline on the growth,nutrient utilization and total cultivable gut microbiota of the red hybrid tilapia,Oreochromis sp., and resistance to Streptococcus agalactiae

A 20‐week feeding trial was conducted to measure growth, nutrient utilization and faecal/gut bacterial counts in triplicate groups of red hybrid tilapia, Oreochromis sp., when fed diets supplemented with 0.5% organic acids blend (OAB), 1.0% OAB, 0.5% oxytetracycline (OTC) or a control diet (no additives). At the end of the feeding trial, tilapia were challenged with Streptococcus agalactiae for 22 days. Fish fed the OTC diet had significantly higher (P < 0.05) growth than the control treatment, while growth between fish fed the OTC or OAB diets was not significantly different (P > 0.05). Phosphorus, dry matter and ash digestibility were significantly higher in the 1.0% OAB diet than the control diet. Fish fed the OAB diets had significantly lower colony‐forming units of adherent gut bacteria compared to the control or OTC treatments while those fed the 1.0% OAB diet had the lowest total faecal bacterial counts. Tilapia fed the 0.5% OTC or OAB diet had significantly higher resistance to S. agalactiae than those fed the control diet. This study indicates that dietary organic acids can potentially replace OTC as a growth promoter and antimicrobial in tilapia feeds.     

Effect of Lactobacillus acidophilussupplementation on growth performances,digestive enzyme activities and gut histomorphology of striped catfish (Pangasianodon hypophthalmusSauvage, 1878) juveniles

The influence of dietary supplementation of Lactobacillus acidophilus, on growth performance, digestive enzyme activities, gut histomorphology and gut microflora were evaluated in juveniles striped catfish (Pangasianodon hypophthalmus). Five experimental diets were formulated by supplementing 0, 10³, 10⁵, 10⁷ and 10⁹ CFU/g L. acidophilus in fishmeal and casein‐based semi‐purified diet. Triplicate groups of striped catfish (21.69 ± 0.18 g) were stocked in 15 fiberglass tanks with stocking density of 25 individuals per tank and fed twice daily at 2.5% of the fish body weight for 12 weeks. Weight gain, specific growth rate, feed conversion ratio and the protein efficiency ratio were significantly higher in fish fed with 10⁵ and 10⁷CFU/g L. acidophilussupplemented diets compared with the other treatment groups. Compared with the control and fish fed low (10³ CFU/g) L. acidophilus supplementation, those fed with 10⁵ and 10⁷ CFU/g had significantly higher (p < 0.05) apparent protein digestibility. Inclusion of L. acidophilus at 10⁷ CFU/g diet significantly increased amylase, protease and lipase activities. Microscopic analysis showed that the villi length in both the anterior and posterior gut and microvilli length in the posterior gut increased significantly in fish fed L. acidophilus supplementation at 10⁵ and 10⁷ CFU/g of diet. The fish fed L. acidophilus supplemented diets significantly increased the total lactic acid bacteria counts in the gut of striped catfish compared with the control‐fed group. Based on gut histomorphology and growth performance, inclusion of L. acidophilus at 10⁵ CFU/g appears to have the most positive effect on striped catfish farming.     

Dietary monosodium glutamate supplementation during the feed training of pacamã (Lophiosilurus alexandri): Growth performance and intestinal histomorphometry

Feed training of carnivorous fish is a delicate and stressful process. Thus, feed additives that reduce stress and encourage fish consumption could improve training efficiency. Therefore, the aim of this study was to evaluate monosodium glutamate (MSG) dietary supplementation during pacamã (Lophiosilurus alexandri) feed training through growth performance and intestinal histomorphometry. Fish were trained by the method of gradual diet transition, using five diets with increasing proportions of commercial diet and decreasing proportions of gelatin. A quadruplicate experimental design was performed with seven treatments, consisted in diets supplemented with different levels of MSG (0.0; 2.0; 8.0; 16.0; 29.0; 34.0 and 42.0 g/kg). Pacamã (0.17 ± 0.01 g) were distributed in 28 tanks (30 fish per tank) and trained for 41 days with the experimental diets. There were no effects (p > .05) of MSG on growth performance and feed training indices. However, fish trained with diets supplemented with 42.0 g/kg of MSG presented higher number of goblet cells in the anterior portion of intestine (p < .05). These results demonstrate that MSG did not act on growth performance and feed training efficiency of pacamã, and high levels of MSG can cause dietary stress on fish intestinal mucosa.     

Symbiotic supplementation on the hemato‐immunological parameters and survival of the hybrid surubim after challenge with Aeromonas hydrophila

This study evaluated the effects of dietary supplementation with two symbiotics in the hybrid surubim (Pseudoplatystoma corruscans × P. reticulatum) prior to and after challenge with Aeromonas hydrophila. The fish were divided into unsupplemented fish, supplemented fish with Weissella cibaria and inulin, and supplemented fish with Lactobacillus plantarum and inulin. Twenty days after being fed symbiotics, the fish were sampled for immunological, haematological, and microbiological analysis pre‐challenge. After this period, they were challenged with Aeromonas hydrophila, and after 96 h the fish were sampled for blood collection and survival. Fish fed W. cibaria and inulin from the pre‐challenge showed the highest values of lysozyme activity. Fish fed L. plantarum and inulin presented a higher number of thrombocytes and granular leukocyte PAS⁺ than the other fish. After challenge, fish fed both symbiotics presented an increased red blood cells number. Fish fed L. plantarum and inulin showed an increased total leucocyte count (WBC), neutrophils, and monocytes number as well as total immunoglobulin. The W. cibaria‐ and inulin‐supplemented fish showed improved haematological and immunological parameters and reduced cumulative mortality after the challenge.     

Feeding fermented soybean meal diet supplemented with taurine to yellowtail Seriola quinqueradiata affects growth performance and lipid digestion

Feeding experiment was conducted to determine whether fermentation and taurine supplementation of soybean meal (SBM) fed to yellowtail improve growth performance and lipid digestion. Six diets were formulated and designated as SBM, SBM supplemented with taurine (SBM + T), SBM fermented by Bacillus spp. (FSBM1), SBM fermented by Lactobacillus spp. (FSBM2), FSBM2 supplemented with taurine (FSBM2 + T), and fish meal (FM). Yellowtail fingerlings with an initial body weight of 42 g were stocked in 200‐L tanks. The fish were fed, each diet was fed twice daily in two separate tanks for 8 weeks. Results showed that lipid digestibility of the SBM diet was significantly lower than that of the FM diet, but SBM diet lipid digestibility was improved by taurine supplementation and fermentation. Lipase activity in anterior intestinal digesta, lipid contents in liver and muscle, and bile acid concentrations in gallbladder and anterior intestinal digesta were significantly lower in fish fed SBM diet than in fish fed FM diet; these parameters were not significantly different between fish fed SBM + T, FSBM2, FSBM2 + T diets and FM diet. Although taurine supplementation or fermentation improved lipid digestibility compared with FM diet, growth parameters were only improved in the fish fed FSBM2 + T diet, indicating that apart from a lack of taurine, SBM contains other factors responsible for inferior growth of yellowtail. These factors can be partially eliminated by Lactobacillus spp. fermentation.     

The effect of dietary chitin on the autochthonous gut bacteria of Atlantic cod ( Gadus morhua L.)

In the present study the impact on autochthonous (adherent) bacteria in proximal intestine (PI) and distal intestine (DI) of Atlantic cod ( Gadus morhua L.) was evaluated following feeding of a control diet and a diet supplemented with 5% chitin. The autochthonous gut bacteria were investigated using denaturing gradient gel electrophoresis (DGGE). Analysis of the microbiota associated with PI and DI of Atlantic cod indicate that dietary chitin modulate the intestinal bacterial community. For example, band 25 ( Escherichia coli–like), band 14 ( Anaerorhabdus furcosa–like) and band 29 (uncultured bacterium–like) in PI were depressed by dietary chitin (P < 0.05). The number of bands (23.7 ± 5.4) in DI of fish fed chitin was marginally higher than the control fish (16.7 ± 2.1) (P = 0.065), and the relative abundances of band 6 (swine faecal bacterium–like) were marginally stimulated by dietary chitin (P = 0.095). Furthermore, the present study reports several novel sequences not previously reported in the gastrointestinal tract of Atlantic cod. Whether the dietary effect of chitin on gut bacterial community has any positive effect of fish health merits further investigations.     

Effects of dietary supplementation of potential probiotic Bacillus subtilis VSG1 singularly or in combination with Lactobacillus plantarum VSG3 or/and Pseudomonas aeruginosa VSG2 on the growth,immunity and disease resistance of Labeo rohita

Labeo rohita fingerlings were fed for 60 days with basal diet (BD) or one of the following experimental diets: DI (BD + B. subtilis); DII (BD + B. subtilis + L. plantarum); DIII (BD + B. subtilis + P. aeruginosa) and DIV (BD + B. subtilis + P. aeruginosa + L. plantarum). Various growth and immune parameters were examined at 30 and 60 days postfeeding. The fish group fed DIV diet had better improvement (P < 0.05) in weight gain, specific growth rate (SGR) and feed conversion ratio (FCR) than the control and other treatment groups. The serum lysozyme activities, alternative complement pathway activity, phagocytic activity and respiratory burst activity in head kidney macrophages of L. rohita increased significantly in the experimental groups throughout the trial period. Superoxide dismutase increased significantly in the experimental groups, except DI fed group, after 60 days of feeding. A significant improvement in serum IgM level was observed in the treatment groups at 30 days of feeding only. Further, fish fed the DIV diet had highest (P < 0.05) postchallenge survival rate (86.6%), followed by DII (73.3%) and DIII (66.6%) against A. hydrophila infection. Considering these promising results, we suggest that a multi‐species probiotic supplementation in equal proportions for 60 days can effectively improve growth and immunity of L. rohita.     

Improvement of growth performance,digestive enzymes and body composition of Persian sturgeon (Acipenser persicus) following feeding on probiotics: Bacillus licheniformis,Bacillus subtilis and Saccharomyces cerevisiae

The individual and combinational effects of probiotics on Persian sturgeon (Acipenser persicus) were evaluated through assessing the growth performance, proximate body composition, digestive enzymes and intestinal morphology. On the basis of feeding with experimental diets, the fish were assigned into four groups denoted as follows: control (basal diet), D‐Pro (basal diet + Bacillus subtilis and Bacillus licheniformis), D‐Pro/Yeast (basal diet + B. subtilis and B. licheniformis + Saccharomyces cerevisiae), Yeast (basal diet + S. cerevisiae). Maximum mean weight and length were measured for the fish fed with D‐pro regime. weight gain (WG), body weight gain (BWI%),  feed efficiency (FE%), protein efficiency rate (PER), lipid efficiency rate (LER), and condition factor (CF) demonstrated the highest values for the fish fed with the diets containing D‐Pro and/or D‐Pro/yeast. LER and food conversion ratio (FCR) showed the highest performance for the fish received the D‐Pro diet. The diets containing D‐Pro exhibited higher performance in enhancing the activity of protease and lipase than the one supplemented only with the yeast, whereas the regimes treated with the yeast exhibited higher amylase activity. The fish received D‐Pro exhibited the highest protein and fat contents, yet did the lowest contents of moisture and total ash. Taken together, the findings revealed that the dietary administration of the D‐Pro and D‐Pro/Yeast could improve the growth performance of A. persicus.     

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

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

Influence of different dietary carbohydrate sources on the growth and intestinal microbiota of Litopenaeus vannamei at low salinity

Because of the increasing market potential of Pacific white shrimp (Litopenaeus vannamei) and limited availability of coastal areas for production, culture of L. vannamei at low salinity is a growing trend throughout the world. Dietary manipulation could improve the growth performance of L. vannamei at low salinity. This study reared L. vannamei with glucose, sucrose and corn starch as dietary carbohydrate sources, respectively, at a low salinity. The results indicated that the sucrose and glucose feeding groups showed better growth performance. An Illumina‐based sequencing method was used to examine the intestinal bacterial composition and the results indicated that Proteobacteria were the most prevalent members, but abundance of Actinobacteria decreased while Firmicutes increased in the corn starch‐fed group. Furthermore, bacteria related to complex carbohydrate degradation were in lower abundance, whereas the abundance of opportunistic pathogenic bacteria increased in corn starch‐fed group than the other two groups, suggesting that the diet imposes selective pressure on the intestinal microbiota. Complex carbohydrates were not the ideal energy sources for L. vannamei at low salinity because the host has higher energy demand in the stressful conditions while the complex carbohydrate degradation efficiency of the gut microbiota in L. vannamei is limited.     

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.     

Development of attenuated erythromycin‐resistant Streptococcus agalactiae vaccine for tilapia (Oreochromis niloticus) culture

Streptococcus agalactiae is an important pathogen in fish, causing great losses of intensive tilapia farming. To develop a potential live attenuated vaccine, a re‐attenuated S. agalactiae (named TFJ‐ery) was developed from a natural low‐virulence S. agalactiae strain TFJ0901 through selection of resistance to erythromycin. The biological characteristics, virulence, stability and the immunization protective efficacy to tilapia of TFJ‐ery were determined. The results indicated that TFJ‐ery grew at a slower rate than TFJ0901. The capsule thickness of TFJ‐ery was significantly less (p < 0.05) than TFJ0901. When Nile tilapia were intraperitoneally (IP) injected with TFJ‐ery, the mortality of fish was decreased than that injected with TFJ0901. The RPS of fish immunized with TFJ‐ery at a dose of 5.0 × 10⁷ CFU was 95.00%, 93.02% and 100.00% at 4, 8 and 16 weeks post‐vaccination, respectively. ELISA results showed that the vaccinated fish produced significantly higher (p < 0.05) antibody titres compared to those of control at 2 or 4 weeks post‐vaccination. Taken together, our results suggest that erythromycin could be used to attenuate S. agalactiae, and TFJ‐ery is a potent attenuated vaccine candidate to protect tilapia against S. agalactiae infections.     

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.     

Morphological characterization of the adherence and invasion of Streptococcus agalactiae to the intestinal mucosa of tilapia Oreochromis sp.: An in vitro model

Streptococcosis in tilapia Oreochromis sp. is possibly the most important bacterial disease for fish production worldwide. In Colombia, streptococcosis is caused by Streptococcus agalactiae (GBS), but in other countries, Streptococcus iniae is also involved. Prevention of streptococcosis is required and must be addressed for economic, social, international trade and public health reasons. This research used an in vitro culture of tilapia intestine to detail the intestinal mucosal response once the pathogen contacts the epithelium. We show that S. agalactiae sheds off its capsule to adhere to the epithelium. The bacterium adheres as a single individuum, in groups or in chains and is able to divide on the apical border of enterocytes. GBS adheres at and invades exclusively through the apical portion of the intestinal folds, using the transepithelial route. Once within the cytoplasm of enterocytes, the bacteria continue to divide. On the basolateral side of the epithelium, the microorganisms leave the cells to reach the propria and travel through the microcirculation. No evidence of an immuno‐inflammatory reaction or goblet cell response in the epithelium or the lamina propria was seen during the process of adherence and invasion of the pathogen.