Bacterial composition,abundance and diversity in fish polyculture and mussel–fish integrated cultured ponds in China

Bacterial community and abiotic environmental parameters in twelve freshwater aquaculture ponds were analysed. According to the major component of stocked animals, the ponds were grouped into four types: black carp Mylopharyngodon piceus, largemouth bass Micropterus salmoides, yellow catfish Pelteobagrus fulvidraco and pearl mussel Hyriopsis cumingii ponds. Each type of pond was stocked with three species of Chinese carps (silver carp, bighead carp and gibel carp) to form a unique mode of fish polyculture or mussel–fish integrated culture. The bacterial composition was identified using 16S rDNA sequencing. Totally, 3701 and 11 150 operational taxonomic units (OTUs) were identified from the water and sediment samples respectively. The number of OTUs, abundance‐based coverage estimator, Chao1 index and Shannon diversity index were lower in the water column than in the sediment, suggesting that diversity and stability of bacterial community were higher in the sediment. In the water column, Proteobacteria, Actinobacteria and Bacteroidetes dominated at the phylum level, and 26 dominant genera were identified. In the sediment, Proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria and Nitrospirae dominated at the phylum level, and 25 dominant genera were identified. Bacterial compositions between the ponds with different aquaculture modes were similar at the phylum levels, but varied at the genus levels. The bacterial composition in the ponds was correlated with hardness, ammonia and total nitrogen in the water column. This study indicates that the type of aquaculture mode is a factor regulating the microbial community, which provides an insight towards microbial management through probiotic manipulation in pond culture.     

凡纳滨对虾养殖环境及肠道微生物群落特征分析

为探究凡纳滨对虾养殖过程中其肠道和养殖环境微生物群落的结构及变化，本实验采用Illumina MiSeq测序平台，基于16S rRNA基因的测序结果，对46和86 d虾龄的凡纳滨对虾肠道以及养殖水样、底泥中的微生物群落进行分析。结果显示，86 d时微生物Shannon-Wiener多样性指数显著高于46 d，水样中的Shannon-Wiener指数显著低于底泥和凡纳滨对虾肠道；有35个门、70个纲、152个目、274个科以及420个属在水样、底泥和虾肠道中均能检测到，其中虾肠道和底泥间共有菌类较水样中更多。微生物群落随养殖时间增加发生变化，46与86 d的差异性门类为放线菌门、绿菌门、丝状杆菌门、浮霉状菌门和TM6，相对丰度随时间增加而增高。水样、底泥和虾肠道中有相对固定的优势菌群，在水样、底泥和虾肠道中主要的门类均为变形菌门、拟杆菌门和放线菌门，优势纲类为α变形菌纲、β变形菌纲以及放线菌纲，除此以外，虾肠道与底泥共有的优势纲为δ变形菌纲、γ变形菌纲以及芽单胞菌纲；从目、科、属的分类水平上看，水样、底泥和虾肠道中菌类相对丰度各异，鲜有明显重叠的优势菌类，在水样、底泥和虾肠道中均为一种未分类的属占优势地位，水样中优势属为hgcI_clade，底泥和虾肠道中优势属为Ambiguous_taxa。研究结果进一步解释了虾肠道和环境微生物群落结构之间的相关性以及随虾龄增长呈现的差异性。     

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

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

Probiotic efficiency of Bacillus sp. in Labeo rohita challenged by Aeromonas hydrophila: assessment of stress profile,haemato‐biochemical parameters and immune responses

Fish are always susceptible to a wide variety of deadly pathogens which cause a huge loss in aquaculture industries. In this investigation, we have demonstrated the in vivo probiotic efficiency of Bacillus sp. MVF1 (GenBank Acc. No. KP256503) in Labeo rohita challenged with pathogenic strain of Aeromonas hydrophila (MTCC 1739). To check the probiotic potential of the selected bacterial strain, fish were divided into four groups: control, D1, D2 and D3. A total of 100 days (70 days probiotic feeding + 71th day sampling and 28 days challenged test + 29th day sampling) of feeding trial was conducted. To establish the probiotic potential of Bacillus sp. MVF1, certain haematological parameters (haemoglobin, total erythrocyte and leucocyte count), serum biochemical parameters (total protein, albumin and globulin), immune parameters (serum lysozyme and total IgM levels) and hepatic stress profile (malondialdehyde production, superoxide dismutase and catalase activity) have been measured. Our results demonstrated that red blood cell number, white blood cell number and haemoglobin content were much higher in D2 group fish compared to other groups and control fish. Similarly, total protein contents, albumin concentration, globulin concentration, lysozyme activity and IgM production were also recorded to be highest in D2 group fish. This finding clearly indicated the probiotic potential of Bacillus sp. MVF1 in L. rohita. Furthermore, our results also demonstrated that 1 × 10⁷ CFU g^?1 feed (D2) provides better immunity compared to 1 × 10⁵ (D1) and 1 × 10⁹ (D3). Due to beneficial effects, the bacterium Bacillus sp. MVF1 might be useful in aquaculture industries to reduce the disease susceptibility.     

Bacterial community composition and distribution in different segments of the gastrointestinal tract of wild‐caught adult Penaeus monodon

Bacterial community associated with the gastrointestinal (GI) tract of aquaculture animals can play important roles in health, nutrition and disease. Compared with the GI tract of aquatic vertebrates such as fish, crustacean GI tract has unique structures and surfaces in different segments that may contribute to differences in the bacterial communities. This study examined the bacterial composition and distribution in different segments along the GI tract and in digesta of wild‐caught adult Penaeus monodon using Automated Ribosomal Intergenic Spacer Analysis (ARISA), real‐time quantitative PCR and clone libraries of 16S rRNA genes. Thirty‐nine bacterial species in four phyla including Proteobacteria (α, β, ε, γ), Firmicutes, Bacteroidetes and Actinobacteria were represented in the GI tract of adult P. monodon. Proteobacteria comprised over 80% abundance of the bacterial community in most segments of the GI tract, except the middle intestine that was dominated by Firmicutes (~50% abundance). The results also showed that bacterial communities showed significant differences along the GI tract segments, particularly the hindgut (p < .001) with Vibrio and Ferrimonas as dominant genera. The knowledge about the distribution of bacteria could be useful in understanding interaction of commensal bacteria and pathogens in different segments, and its potential influence on the effectiveness of probiotic bacteria in the GI tract of shrimp.     

Effects of feeding regime and probionts on the diverting microbial communities in rotifer Brachionus culture

Rotifer growth performance and microbial community changes associated with rotifer cultures were monitored while different feed types (Nannochloropsis oculata paste and the commercial yeast based feed CS-3000), different regimes (daily changes, changes per batch and no changes) and mixtures of three probionts (Phenylobacterium sp.; Gluconobacter sp. and Paracoccus denitrificans) were provided. It was shown that the dominant bacterial species in the cultures receiving either N. oculata or CS-3000 were different. However, in cultures receiving both feeds (either switching between feeds on a daily basis or on a batch basis), a high similarity in microbial community fingerprint was found. The presence of probionts was detected by the end of four batch culture cycles in spite of strong shifts of the bacterial community. By group discriminant analysis, it was found that Phenylobacterium sp. and Paracoccus sp. contributed positively to the CS-3000-fed group, while Gluconobacter sp. contributed positively to the N. oculata-fed group, although they did not appear as very dominant species.     

Effects of dietary marine microalgae,Tetraselmis suecica,on production,gene expression,protein markers and bacterial count of Pacific white shrimp Litopenaeus vannamei

The marine flagellated Chlorophyta Tetraselmis suecica is among the most important live food species in marine aquaculture. In the present study, the effects of dietary supplementation of dried marine microalgae, Tetraselmis suecica, on growth performance; feed utilization; chemical composition; gene expression of superoxide dismutase (SOD), glutathione peroxidase (GPx) and insulin‐like growth factor 2 (IGF‐II) gene of Pacific white shrimp, Litopenaeus vannamei; muscle protein polymorphism; and microbial count were assessed and evaluated. Three hundred and sixty L. vannamei (postlarvae) Pls (0.124 ± 0.002 g) were randomly stocked into 40‐L glass aquaria (30 shrimp/aquarium) and fed three times daily four tested diets: a basal diet (control), diet incorporated with 2.5 g kg^?1 dried T. suecica (T1), 5 g kg^?1 dried T. suecica (T2) and 7.5 g kg^?1 dried T. suecica (T3) in triplicates, for 90 days. At the end of the trial, the survival rate (SR) of L. vannamei fed diets supplemented with different levels of T. suecica was significantly (p < .05) higher than the control diet. The highest weight gain and specific growth rate and the best feed conversion ratio were recorded on L. vannamei fed a diet supplemented with a 7.5 g/kg dried T. suecica. The highest protein, lipid and ash contents were obtained in L. vannamei fed the diet containing 7.5 g/kg T. suecica, when compared with the remaining tested diets. The gene expression of antioxidant genes SOD and GPx was the lowest in the T3 group in comparison with the control group. Meanwhile, expression level of IGF‐II was higher in the T2 group. The total heterotrophic bacterial count was significantly (p < .05) increased with the cumulative T. suecica level, while no significant (p > .05) differences were found in the total Vibrio count among treatments. Overall, the present results have shown that the diet supplemented with the highest inclusion level of dried T. suecica resulted in improved growth and nutrient utilization.     

Improvement of growth performance,water quality and disease resistance against Vibrio harveyi of postlarval whiteleg shrimp (Litopenaeus vannamei) by administration of mixed microencapsulated Bacillus probiotics

The objective of this study was to investigate the effects of mixed Bacillus on growth, water quality and disease resistance against Vibrio harveyi in whiteleg shrimp (Litopenaeus vannamei). Postlarval shrimp (PL₃₀) were fed with (a) a basal diet (the control), (b) a diet containing mixed freeze‐dried Bacillus probiotics (FB) and (c) addition of mixed microencapsulated Bacillus probiotics (MB) in culture water. Addition of FB and MB probiotics improved (p < .05) growth, feed efficiency, survival and culture water quality (ammonia and nitrite) compared to the control group although there was no difference (p > .05) between the two treated groups. Bacillus numbers in gastrointestinal tracts and culture water of FB‐ and MB‐administrated shrimp were higher (p < .05) than in the control. After a 30‐day culture, shrimp were infected with V. harveyi and monitored for 10 days. A significant reduction (p < .05) in cumulative mortality was observed in FB‐ and MB‐supplemented shrimp (43.24% and 45.05%, respectively), compared to the control (63.06%). This finding demonstrated that administration of microencapsulated probiotics was as effective as freeze‐dried probiotics for improving growth, feed efficiency, survival, Bacillus in gastrointestinal tracts, water quality (ammonia and nitrite) and conferring disease resistance to V. harveyi.     

Productive performance of juvenile freshwater prawns Macrobrachium rosenbergii in biofloc system

The aim of this study was to compare two rearing systems for freshwater prawn Macrobrachium rosenbergii: one with use of a recirculating aquaculture system with biofilters (RAS) and another with use of microbial flocs (F). Thirty postlarvae of freshwater prawn with an initial average weight of 0.13 ± 0.05 g were randomly stocked in six experimental units with 0.20 m² and volume of 50 L. The experiment lasted thirty days. Dissolved oxygen, temperature and pH were monitored daily; ammonia concentration was determined three times per week; nitrite concentration, alkalinity and hardness were measured weekly. For the formation of microbial floc, molasses was used to keep the ammonia concentrations within safe levels for prawn farming. The variables of water quality remained within the suitable range for the production of the species, except for ammonia concentrations at the F treatment, which exceeded the safe levels. At the end of the experiment, the following parameters were evaluated: survival, specific growth rate, weight gain and feed conversion rate. Differences were found only in feed conversion rate with better values on RAS treatment. The microorganisms present in the RAS and F treatment were also evaluated. The densities of rotifers, amoebas and total bacteria were higher at the F treatment although the same organisms were found at the RAS treatment. The results of this study showed the possibility of rearing M. rosenbergii in biofloc system technology.     

Effects of Inorganic and Organic Fertilization on Physicochemical Parameters,Bacterial Concentrations,and Shrimp Growth in Litopenaeus vannamei Cultures with Zero Water Exchange

To identify ways to improve water quality and shrimp production in closed systems, two parallel experiments (one in tanks and one in ponds) were conducted using Pacific white shrimp, Litopenaeus vannamei, cultures. In both experiments, the effects of inorganic (Nutrilake®) and organic (molasses) fertilization on physicochemical parameters, bacterial concentrations, and shrimp performance under zero water exchange were evaluated. Fertilization with both molasses and Nutrilake enhanced the feed conversion rate, as well as shrimp survival and production. In tanks, the shrimp survival and production rates were highest in the molasses treatment, but this effect was not observed in ponds. In ponds, fertilization with Nutrilake increased nitrogen and phosphorus concentrations more than did the controls and molasses treatments toward the end of the experiment. In tanks, fertilization with molasses reduced ammonia concentrations toward the end of the experiment, but the same effect was not observed in ponds. In ponds, fertilization reduced the proportion of Vibrio spp. bacteria, which most likely reduced the incidence of disease from these potentially pathogenic organisms. In both culture systems, fertilization increased the proportion of Bacillus spp., which most likely enhanced food availability.