Immune response and disease resistance of shrimp fed biofloc grown on different carbon sources

Unveiling the biofloc culture potential: Harnessing immune functions for resilience of shrimp and resistance against AHPND -causing Vibrio parahaemolyticus infection

In shrimp aquaculture, disease mitigation may be accomplished by reducing the virulence of the pathogen or by boosting the shrimp's immunity. Biofloc technology is an innovative system that improves the health and resistance of shrimp to microbial infections while providing a viable option for maintaining the quality of culture water through efficient nutrient recycling. This review aimed at demonstrating the efficacy of the biofloc system in boosting the immune responses and protective processes of shrimp against Vibrio parahaemolyticus infection, which is known to cause Acute Hepatopancreatic Necrosis Disease (AHPND). Numerous studies have revealed that the biofloc system promotes the immunological capability of shrimp by raising multiple immune -related genes e.g. prophenoloxidase, serine proteinase gene, ras-related nuclear gene and penaeidinexpression and cellular and humoral responses such as hyperaemia, prophenoloxidase activity, superoxide dismutase activity, phagocytic activity; the protection and survival of shrimp when faced with a challenge from the V. parahaemolyticus strain have been enhanced. Furthermore, the use of the biofloc system improves water quality parameters and potentially bolstering their immune and overall health to effectively resist diseases; hence, promotes the growth of shrimp. The present review suggests that biofloc can serve as an effective therapy for both preventing and supporting the management of probable AHPND infection in shrimp culture. This approach exhibits potential for the progress of sustainable shrimp farming, higher productivity, and improved shrimp health.

Enhancing Florida red tilapia aquaculture: biofloc optimization improves water quality, pathogen bacterial control, fish health, immune response, and organ histopathology across varied groundwater salinities

Freshwater scarcity poses challenges to aquaculture worldwide, including countries like Egypt. In this study, we investigate the feasibility of integrating underground saline water (USW) with varying salinities into a Biofloc (BFT) system for desert mariculture of Florida red tilapia (FRT) and its impacts on water quality, fish performance and health. Four BFT treatments (C/N ratio = 15) were examined in triplicate using four salinity levels 0 ppt, 12 ppt, 24 ppt and 36 ppt, expressed as S0, S12, S24 and S36, respectively. For 75 days, a total of 12 fiberglass tanks (each 250 L-1 water) were used to store FRT fry (average weight of 1.73 ± 0.01 g/fish). The fish were fed an experimental diet (protein/fat = 30/5) and an additional carbon source of rice bran. The results revealed that group S12 showed better growth indicators, higher survival rate, lower FCR, and lower ammonia levels, while group S0 exhibited lower growth indicators (final weight, weight gain, and specific growth rate) than all groups. The serum kidney, liver, and antioxidant indices performed better in the S12 group. At 12 ppt, the immune-related parameter (IgM) increased by 22.5%, while the stress parameter (cortisol) decreased by 40.8% compared to the S0 group. The liver and intestinal histopathological results revealed that the S12 and S24 groups performed better. Pathogenic bacterial load counts favored the S24 group, which had the lowest number among the groups studied. The recommended salinity for FRT cultivation in USW and BFT is 19.94-20 ppt, determined by polynomial regression of FW and FCR.

Unveiling the positive impact of biofloc culture on Vibrio parahaemolyticus infection of Pacific white shrimp by reducing quorum sensing and virulence gene expression and enhancing immunity

This study aimed to evaluate and unveil the positive impact of biofloc culture on Vibrio parahaemolyticus infection of Pacific white shrimp by reducing quorum sensing (QS) and virulence gene expression and enhancing shrimp's immunity. The shrimp with an average body weight of 0.50 ± 0.09 g were reared in containers with a volume of 2.5 L, 21 units, and a density of 20 shrimp L-1. The shrimp were cultured for 5 days, with each treatment including biofloc system maintenance with a C/N ratio of 10 and a control treatment without biofloc, followed by a challenge test through immersion using V. parahaemolyticus at densities of 103, 105, and 107 CFU mL-1 initially. The results of the in vitro experiment showed that biofloc suspension can inhibit and disperse biofilm formation, as well as reduce the exo-enzyme activity (amylase, protease, and chitinase) of V. parahaemolyticus. Furthermore, the biofloc treatment significantly reduced the expression of the QS regulatory gene OpaR, the PirB toxin gene, and the virulence factor genes T6SS1 and T6SS2 in both in vitro and in vivo. The biofloc system also increased the expression of shrimp immunity-related genes (LGBP, proPO, SP, and PE) and the survival rate of white shrimp challenged with V. parahaemolyticus.

Influence of stocking density on the growth, immune and physiological responses, and cultivation environment of white-leg shrimp (Litopenaeus vannamei) in biofloc systems

Biofloc (BF) stands out as a promising system for sustainable shrimp farming. Optimizing various culture conditions, such as stocking density, carbohydrate source, and feeding management, is crucial for the widespread adoption of the BF system. This study compares the growth performance of white-leg shrimp (Litopenaeus vannamei) in culture ponds at low density (LD) with 50 organisms/m2 and high density (HD) with 200 organisms/m2. Post-larvae of white-leg shrimp were stocked for 16 weeks in both LD and HD groups. The LD group exhibited a superior survival rate, growth rate, and feed consumption compared to the HD group. The BF from the LD system recorded a significantly higher protein content (16.63 ± 0.21%) than the HD group (15.21 ± 0.34%). Heterotrophic bacterial counts in water did not significantly differ with stocking density. However, Vibrio count in water samples was higher in the HD group (3.59 ± 0.35 log CFU/mL) compared to the LD group (2.45 ± 0.43 log CFU/mL). The whole shrimp body analysis revealed significantly higher protein and lipid content in the LD group. In contrast, the total aerobic bacterial count in shrimp from the HD group was high, with the identification of Salmonella enterica ssp. arizonae. Additionally, Vibrio counts in shrimp samples were significantly higher in the HD group (4.63 ± 0.32 log CFU/g) compared to the LD group (3.57 ± 0.22 log CFU/g). The expression levels of immune-associated genes, including prophenoloxidase, transglutaminase, penaiedin 3, superoxide dismutase, lysozyme, serine proteinase, and the growth-related gene ras-related protein (rap-2a), were significantly enhanced in the LD group. Conversely, stress-related gene expression increased significantly in the HD group. Hepatopancreases amylase, lipase, and protease were higher in the LD group, while trypsin activity did not differ significantly. Antioxidant enzyme activity (catalase, glutathione, glutathione peroxidase, and superoxide dismutase) significantly increased in the LD group. The histological structure of hepatopancreas, musculature, and female gonads remained similar in both densities. However, negative effects were observed in the gills' histology of the HD group. These results suggest that increasing stocking density is associated with significantly negative biological, microbial, and physiological effects on white-leg shrimp under the BF system.

Host-microbiome interaction in fish and shellfish: An overview

The importance of the gut microbiome in the management of various physiological activities including healthy growth and performance of fish and shellfish is now widely considered and being studied in detail for potential applications in aquaculture farming and the future growth of the fish industry. The gut microbiome in all animals including fish is associated with a number of beneficial functions for the host, such as stimulating optimal gastrointestinal development, producing and supplying vitamins to the host, and improving the host's nutrient uptake by providing additional enzymatic activities. Besides nutrient uptake, the gut microbiome is involved in strengthening the immune system and maintaining mucosal tolerance, enhancing the host's resilience against infectious diseases, and the production of anticarcinogenic and anti-inflammatory compounds. Because of its significant role, the gut microbiome is very often considered an "extra organ," as it plays a key role in intestinal development and regulation of other physiological functions. Recent studies suggest that the gut microbiome is involved in energy homeostasis by regulating feeding, digestive and metabolic processes, as well as the immune response. Consequently, deciphering gut microbiome dynamics in cultured fish and shellfish species will play an indispensable role in promoting animal health and aquaculture productivity. It is mentioned that the microbiome community available in the gut tract, particularly in the intestine acts as an innovative source of natural product discovery. The microbial communities that are associated with several marine organisms are the source of natural products with a diverse array of biological activities and as of today, more than 1000 new compounds have been reported from such microbial species. Exploration of such new ingredients from microbial species would create more opportunities for the development of the bio-pharma/aquaculture industries. Considering the important role of the microbiome in the whole life span of fish and shellfish, it is necessary to understand the interaction process between the host and microbial community. However, information pertaining to host-microbiome interaction, particularly at the cellular level, gene expression, metabolic pathways, and immunomodulation mechanisms, the available literature is scanty. It has been reported that there are three ways of interaction involving the host-microbe-environment operates to maintain homeostasis in the fish and shellfish gut i.e. host intrinsic factors, the environment that shapes the gut microbiome composition, and the core microbial community present in the gut system itself has equal influence on the host biology. In the present review, efforts have been made to collect comprehensive information on various aspects of host-microbiome interaction, particularly on the immune system and health maintenance, management of diseases, nutrient uptake, digestion and absorption, gene expression, and metabolism in fish and shellfish.

Microbial inoculums improve growth and health of Heteropneustes fossilis via biofloc-driven aquaculture

Biofloc technology aims to maximize fish farming productivity by effectively breaking down ammonia and nitrite, promoting healthy flocculation, and enhancing the growth and immunity of cultured animals. However, a major limitation in this field is the suitable starter microbial culture and narrow number of fish species that have been tested with the biofloc system. Here, we investigated various microbial inoculum containing beneficial microbes with probiotics, immunostimulatory and flocs development and bioremediation properties would lead to the development of ideal biofloc development. Three treatment groups with different microbial combinations, viz., group 1 [Bacillus subtilis (AN1) + Pseudomonas putida (PB3) + Saccharomyces cerevisiae (ATCC-2601)], group 2 [B. subtilis (AN2) + P. fluorescens (PC3) + S. cerevisiae (ATCC-2601)] and group 3 [B. subtilis (AN3) + P. aeruginosa (PA2) + S. cerevisiae (ATCC-2601)] were used and compared with the positive control (pond water without microbial inoculums) and negative control (clear water: without microbial inoculums and carbon sources) on biofloc development and its characteristic features to improve the water quality and growth of fish. We demonstrated that microbial inoculums, especially group 2, significantly improve the water quality and microbiota of flocs and gut of the test animal, Heteropneustes fossilis. The study further demonstrates that biofloc system supplemented with microbial inoculums positively regulates gut histomorphology and growth performance, as evidenced by improved villous morphology, amylase, protease and lipase activity, weight gain, FCR, T3, T4 and IGF1 levels. The inoculums induced an antioxidative response marked by significantly higher values of catalase (CAT) and superoxide dismutase (SOD) activity. Furthermore, the supplementation of microbial inoculums enhances both specific and non-specific immune responses and significantly elevated levels of immune genes (transferrin, interleukin-1β and C3), and IgM was recorded. This study provides a proof-of-concept approach for assessing microbial inoculums on fish species that can be further utilized to develop biofloc technology for use in sustainable aquaculture.

Biofloc technology and immune response of penaeid shrimp: A meta-analysis and meta-regression

Biological flocs develop as heterogenious communities of detritus, heterotrophic and autotrophic bacteria, algae, fungi and a variety of other things through appropriate management of the carbon-nitrogen ratio in aquaculture farming systems. These microbial communities improve the water quality, reduce the concentrations of toxic inorganic species, and act as a source of food and immunostimulants. However, the information about their role as immunostimulants is widely variable. To obtain a clearer view of the situation, it is necessary to summarize the current literature on this topic through a quantitative review analysis: a meta-analysis. The present work aims to evaluate the effect of biofloc technology (BFT) implementation on culture water quality through meta-analysis, meta-regression, and correlation analysis. Pubmed, Science Direct, Scopus, and Google Scholar were searched from 2000 to 2022 on the influence of BFT on immunological parameters. Three hundred and thirty-four of the scientific articles used BFT for penaeid shrimp, but only 25 articles met the inclusion criterion of using BFT to evaluate its effect on the shrimp's immunity. The current analysis found that the use of BFT stimulates all the evaluated immunological parameters. Also, meta-regression with fixed data of study parameters showed that slow-release carbon sources, probiotics, and an estimated carbon/nitrogen ratio of 10 potentiated a larger effect on BFT immune stimulation. The meta-analysis demonstrated that the volumes of the settleable solids (SS) and the total suspended solids (TSS) are crucial for the effect of BFT on the shrimp immune system. When TSS was higher than 294 mg/L, the respiratory metabolism of the shrimp was compromised. The analysis found evidence of publication biases, indicating that the data had to be interpreted carefully. Nonetheless, this meta-analysis shows that the data quality was sound and the approach used was appropriate; moreover, it also showed that BFT can be an environmentally friendly alternative culture method that enhances the shrimp's immune system.

A detailed look at the impacts of biofloc on immunological and hematological parameters and improving resistance to diseases

The innate immunity of invertebrates serves as a critical trait that provides a valuable foundation for studying the common biological responses to environmental changes. With the exponential growth of the human population, the demand for protein has soared, leading to the intensification of aquaculture. Regrettably, this intensification has resulted in the overuse of antibiotics and chemotherapeutics, which have led to the emergence of resistant microbes or superbugs. In this regard, biofloc technology (BFT) emerges as a promising strategy for disease management in aquaculture. By harnessing the power of antibiotics, probiotics, and prebiotics, BFT offers a sustainable and eco-friendly approach that can help mitigate the negative impacts of harmful chemicals. By adopting this innovative technology, we can enhance the immunity and promote the health of aquatic organisms, thereby ensuring the long-term viability of the aquaculture industry. Using a proper carbon to nitrogen ratio, normally adding an external carbon source, BFT recycles waste in culture system with no water exchange. Heterotrophic bacteria grow along with other key microbes in the culture water. Heterotrophs play a major role in assimilating ammonia from feed and fecal waste, crucial pathway to form suspended microbial aggregates (known as 'biofloc'); while chemoautotrophs (e.g. nitrifying bacteria) oxidize ammonia into nitrite, and nitrite into nitrate promoting a healthy farming conditions. By using a highly aerated media and an organic substrates that contain carbon and nitrogen, protein-rich microbes are able to flocculate in culture water. Several types of microorganisms and their cell components have been studied and applied to aquatic animals as probiotics or immunostimulants (lipopolysaccharide, peptidoglycan, and 1-glucans) to enhance their innate immunity and antioxidant status, thereby enhancing their resistance to disease. In recent years, many studies have been conducted on the application of BFT for different farmed aquatic species and it has been observed as a promising method for the development of sustainable aquaculture, especially due to less use of water, increased productivity and biosecurity, but also an enhancement of the health status of several aquaculture species. This review analyses the immune status, antioxidant activity, blood and biochemical parameters, and level of resistance against pathogenic agents of aquatic animals farmed in BFT systems. This manuscript aims to gather and showcase the scientific evidences related to biofloc as a 'health promoter' in a unique document for the industry and academia.

Establecimiento de biofloc a tres relaciones carbono/nitrógeno, tendiente a la producción de zooplancton

El objetivo de esta investigación fue establecer el biofloc a tres relaciones carbono/ nitrógeno (C/N): 10/1, 15/1 y 20/1, determinando la secuencia de remoción de N, el perfil de sólidos y la caracterización del zooplancton, para tal fin se dispuso de tres tanques con volumen de 7000 L, incorporando oxígeno al agua a través de un aireador tipo soplador. Se utilizó como fuente de N balanceado, fuente de carbono melaza y bicarbonato de sodio como fuente alcalinizante. Al inicio se incrementó el nitrógeno amoniacal total NAT a 2 mg/L, la alcalinidad total (AT) a 120 mg/L y se adicionó como inóculo 10 litros/tanque de agua proveniente de un estanque de cultivo, al sexto y décimo días se adicionó balanceado incrementando teóricamente el NAT en 4 mg/L y a partir del día 12 en 1 mg/L. En las tres relaciones C/N se evidenciaron procesos de nitrificación durante la estabilización del biofloc, hasta llegar en el tiempo a concen­traciones no letales de amonio y nitrito para peces, menores a 1 mg/L. En cuanto a los sólidos volátiles, se encontró una mayor concentración en la relación 20/1, lo cual puede atribuirse a la mayor adición de melaza, con la consecuente producción de SSV a partir de la dominancia de comunidades heterotróficas, en los tres macrocosmos se presentaron comunidades del zooplancton, no obstante, el T2 presentaron la mayor abundancia y riqueza de organismos. Las tres relaciones C/N en biofloc establecieron condiciones de calidad de agua y alimento vivo.

The Optimization of Dietary Protein Level and Carbon Sources on Biofloc Nutritive Values, Bacterial Abundance, and Growth Performances of Whiteleg Shrimp (Litopenaeusvannamei) Juveniles

A biofloc technology-based 75-day indoor growth trial in an 80 L glass aquaria was conducted to evaluate the effects of two different carbon sources (sugarcane bagasse, SB, and wheat flour, WF) on the biofloc composition, bacterial abundance, and growth of whiteleg shrimp (Litopenaeus vannamei) juveniles (0.23 ± 0.04 g). Three different levels of dietary protein content (250, 300, and 350 g protein kg−1 diet) and two carbon sources (SB and WF) were applied (SB250, WF250, SB300, WF300, SB350, and WF350, respectively), comparing to a controlled diet without biofloc and fed on a 450 g protein kg−1 diet (C450). With the addition of SB and WF, water quality was in the ideal recommended ranges for L. vannamei culture. At the end of the experiment, the biofloc volume increased with increasing dietary protein levels. The nutritional value of biofloc in different treatments was influenced by dietary protein and added SB and WF. Increasing dietary protein significantly increased the protein and lipid contents of the produced biofloc. The use of WF as a carbon source significantly increased lipids and nitrogen-free extract in the biofloc. The total heterotrophic bacterial (THB) count was significantly higher (p < 0.05) in WF300 and WF350 than in the other treatments. The mean effect of the protein levels and carbon source was significantly reported, whereas the highest significant THB count was recorded with 300 dietary protein and using WF as a carbon source. The growth performances of L. vannamei fed with biofloc treatments were significantly (p < 0.05) higher than the C450 group. The highest final weight and weight gain were recorded in SB350 treatment. The feed conversion ratio was not affected by reducing dietary protein levels; meanwhile, the protein efficiency ratio increased significantly in biofloc treatments than in the control. Overall, the results demonstrate that, compared to the control treatment of 450 dietary protein, the biofloc treatments using WF as a carbon source could compensate for the reduction in the dietary protein levels in the diet of L. vannamei and maintain higher zootechnical performance.

Evaluation of Salipiger thiooxidans and Exiguobacterium aestuarii from the Saemangeum Reservoir as Potential Probiotics for Pacific White Shrimp (Litopenaeus vannamei)

In this study, two bacterial species, Salipiger thiooxidans and Exiguobacterium aestuarii, were extracted and screened from the Saemangeum Reservoir. This study examined these species’ suitability as a probiotic by confirming the effects of S. thiooxidans and E. aestuarii added to rearing water for L. vannamei. Three experimental groups were evaluated for 6 weeks: (1) a control group reared in natural (i.e., untreated) water (CON), (2) an experimental group in which S. thiooxidans was added to natural water (SMG-A), and (3) natural water inoculated with E. aestuarii (SMG-B). The SMG-B group inoculated with E. aestuarii showed significantly higher final body weight, weight gain, specific growth rates, and feed efficiency than the control group. The SMG-B group inoculated with E. aestuarii exhibited significantly higher levels of serum lysozyme, and ACP and ALP activity than the control and SMG-A groups. The SMG-A and SMG-B groups inoculated with probiotics showed significantly lower total ammonia nitrogen and nitrite than the control group. Our findings suggest that S. thiooxidans and E. aestuarii extracted from the Saemangeum Reservoir can improve the water quality of aquaculture water, and, in particular, E. aestuarii is a potential probiotic for L. vannamei.

Protective effects of the biofloc system in Pacific white shrimp (Penaeus vannamei) culture against pathogenic Vibrio parahaemolyticus infection

The mitigation of vibriosis in shrimp culture could be accomplished by reducing the virulence of the pathogen or by increasing the immune response of the shrimp. This study aims to evaluate the application of a biofloc system in protecting Pacific white shrimp (Penaeus vannamei) from pathogenic Vibrio parahaemolyticus infection. Shrimp post-larvae (PL 20) with an average body weight of 0.041 ± 0.019 g were reared in an aquarium with a working volume of 33 L at a density of 3 L^-1 for 21 days using two rearing systems, i.e., the biofloc system and the regular clear water system as control. In each system, the shrimp post-larvae were challenged by adding V. parahaemolyticus at different densities, 10³, 10⁵, and 10⁷ CFU mL^-1, while the negative control was performed by maintaining shrimp post-larvae in the clear water system without the addition of V. parahaemolyticus. The results of the in vitro experiment showed that the density and biofilm activity of V. parahaemolyticus reared in biofloc suspension was lower than that of the positive control (p < 0.05). The density of V. parahaemolyticus in shrimp rearing water was lower than that in the control at 10⁵ CFU mL^-1, especially on the 3rd day post-challenge, but there was no significant difference in the total presumptive Vibrio count between the biofloc treatment and the control. The survival, growth, and immune response parameters, such as total hemocyte count, phagocytic activity, respiratory burst, and phenoloxidase activity, of the shrimp, reared in the biofloc system were also higher than those of the positive control (p < 0.05), regardless of the density of V. parahaemolyticus. The present study demonstrated that the application of biofloc could significantly protect and increase the resistance of Pacific white shrimp against pathogenic V. parahaemolyticus infection.

A Biofloc-Based Aquaculture System Bio-augmented with Probiotic Bacteria Bacillus tequilensis AP BFT3 Improves Culture Environment, Production Performances, and Proteomic Changes in Penaeus vannamei

Experiments were conducted to evaluate the probiotic effect of bio-augmented Bacillus tequilensis AP BFT3 on improving production, immune response, and proteomic changes of Penaeus vannamei reared in a biofloc system. Penaeus vannamei larvae (PL13) were stocked in 100-L tanks at a rate of 100 no per tank to study the effect of B. tequilensis AP BFT3 with and without biofloc (BFT-PRO and PRO). Control tanks devoid of probiotic strain were maintained in a clear water system. The growth and survival considerably increased in probiotic added biofloc reared shrimp than probiotic added clear water reared ones and control. Water quality significantly improved in probiotic added (PRO) and biofloc-probiotics (BFT-PRO) system than control. Microbiological investigations indicate increased heterotrophic bacterial load in BFT-PRO compared to the PRO and control. The quality of the isolated microbes was analyzed in terms of enzyme production, and an abundance of enzyme-producing bacterial population was observed in BFT-PRO shrimp. Immune-related genes were significantly upregulated in BFT-PRO shrimp, followed by the PRO and control. The proteomic data (2D gel electrophoresis and MALDI-TOF) of muscle tissue from the experimental animals identified 11 differentially expressed proteins. The Daxx OS and Lit v 1 tropomyosin was found upregulated in BFT-PRO shrimps. Downregulation of Na⁺/K⁺ATPase was observed in biofloc with probiotic-supplied groups. The findings revealed that the BFT system's efficacy could be improved through the addition of probiotics. The addition of B. tequilensis AP BFT3 as a probiotic in biofloc induced the expression of essential proteins, reducing contracting diseases during culture.

Biofloc Microbiome With Bioremediation and Health Benefits

The biofloc system has recently attracted great attention as a cost-effective, sustainable, and environmentally friendly technology and expected to contribute toward human food security (Zero Hunger SDG 2). It is also expected that this endeavor can be adopted widely because of its characteristics of zero water exchange and reduced artificial feeding features. In the biofloc system, the flocs which are generally formed by aggregation of heterotrophic microorganisms, serve as natural bioremediation candidates. These microbes effectively maintain water quality by utilizing the nutrient wastes, mostly originated from digested, unconsumed, and metabolic processes of feed. Additionally, the flocs are important sources of nutrients, mainly a protein source, and when these are consumed by aquaculture animals they improve the growth performance, immunity, and disease tolerance of host against pathogenic microbial infection. Here in this review, we focus on recent advances that could provide a mechanistic insight on how the microbial community developed in the biofloc system helps in the bioremediation process and enhances the overall health of the host. We have also tried to address the possible role of these microbial communities against growth and virulence of pathogenic microbes.

Dietary inclusion of watermelon rind powder and Lactobacillus plantarum: Effects on Nile tilapia's growth, skin mucus and serum immunities, and disease resistance

An eight-week investigation was conducted to access the potential impact of dietary watermelon rind powder (WMRP) and L. plantarum CR1T5 (LP) administered individually or in combination on immunity, disease resistance, and growth rate of Nile tilapia fingerlings cultured in a biofloc system. Three hundred twenty fish (average weight 16.57 ± 0.14 g) were distributed into 16 tanks at a rate of 20 fish per tank. The fish were fed different diets: Diet 1 (0 g kg^-1 WMRP and 0 CFU g^-1 L. plantarum) (control), Diet 2 (40 g kg^-1 WMRP), Diet 3 (10⁸ CFU g^-1 LP), and Diet 4 (40 g kg^-1 WMRP + 10⁸ CFU g^-1 LP) for eight weeks. A completely randomized design (CRD) with four replications was applied. Skin mucus, serum immunity, and growth parameters were analyzed every 4 weeks, and a challenge study against S. agalactiae was conducted at the end of the experiment. The findings showed that the inclusion of WMRP + LP, administrated individually or in a mixture, significantly (P<0.05) stimulated growth, skin mucus, and serum immune parameters of Nile tilapia fingerlings compared with the control. The highest values were detected in fish fed the combination of WMRP and LP, as opposed to individual administration of either WMRP or LP, in which no significant differences were detected. Within the challenge study, the relative percent survival (RPS) in Diet 2, Diet 3, and Diet 4 was 48.0%, 52.0%, and 68.0%, respectively. Fish fed 40 g kg^-1 WMRP + LP produced significantly higher RPS and protection against S. agalactiae than the other treated groups. Current results suggest that the dual administration of WMRP and LP maybe an effective feed additive for Nile tilapia grown in an indoor biofloc system, capable of improving growth parameters and increasing resistance to S. agalactiae infection.

Modulation of growth, innate immunity, and disease resistance of Nile tilapia (Oreochromis niloticus) culture under biofloc system by supplementing pineapple peel powder and Lactobacillus plantarum

Eight weeks feeding experiment was managed to evaluate the impacts of dietary addition of pineapple peel powder (PAPP) and Lactobacillus plantarum CR1T5 (LP) individual or mixed on growth performance, skin mucus and serum immunities, as well as disease resistance of Nile tilapia. Fish (average weight 20.91 ± 0.11 g) were fed four diets: Diet 1 (0 g kg^-1 PAPP and 0 CFU g^-1 L. plantarum, Diet 2 (10 g kg^-1 PAPP), Diet 3 (10⁸ CFU g^-1L. plantarum), and Diet 4 (10 g kg^-1 PAPP + 10⁸ CFU g^-1L. plantarum). Serum and mucus immune responses, as well as growth rate, were assessed every 4 weeks. Ten fish were chosen for the challenge test with Streptococcus agalactiae after 8 weeks post-feeding. The findings showed that PAPP and/or LP diets increased (P ≤ 0.05) growth performance, skin mucus, and serum immune responses. The best data were obtained in fish fed a mixture of PAPP and LP. Nevertheless, no variation (P > 0.05) was recorded between groups fed PAPP or LP. The relative survival percentage (RSP, %) in Diet 2, Diet 3, and Diet 4 was 46.15%, 50.0%, and 73.08%. Fish fed mixture of PAPP + LP recorded the best (P < 0.05) survival rate versus other treatments. The current findings recommended using a mixture of PAPP and LP as promising functional additives for aquaculture practice.

Acute Hepatopancreatic Necrosis Disease (AHPND): Virulence, Pathogenesis and Mitigation Strategies in Shrimp Aquaculture

Shrimp, as a high-protein animal food commodity, are one of the fastest growing food producing sectors in the world. It has emerged as a highly traded seafood product, currently exceeding 8 MT of high value. However, disease outbreaks, which are considered as the primary cause of production loss in shrimp farming, have moved to the forefront in recent years and brought socio-economic and environmental unsustainability to the shrimp aquaculture industry. Acute hepatopancreatic necrosis disease (AHPND), caused by Vibrio spp., is a relatively new farmed penaeid shrimp bacterial disease. The shrimp production in AHPND affected regions has dropped to ~60%, and the disease has caused a global loss of USD 43 billion to the shrimp farming industry. The conventional approaches, such as antibiotics and disinfectants, often applied for the mitigation or cure of AHPND, have had limited success. Additionally, their usage has been associated with alteration of host gut microbiota and immunity and development of antibiotic resistance in bacterial pathogens. For example, the Mexico AHPND-causing V. parahaemolyticus strain (13-306D/4 and 13-511/A1) were reported to carry tetB gene coding for tetracycline resistance gene, and V. campbellii from China was found to carry multiple antibiotic resistance genes. As a consequence, there is an urgent need to thoroughly understand the virulence mechanism of AHPND-causing Vibrio spp. and develop novel management strategies to control AHPND in shrimp aquaculture, that will be crucially important to ensure food security in the future and offer economic stability to farmers. In this review, the most important findings of AHPND are highlighted, discussed and put in perspective, and some directions for future research are presented.

Effects on the survival rates, hematological parameters, and neurotransmitters in olive flounders, Paralichthys olivaceus, reared in bio-floc and seawater by Streptococcus iniae challenge

Bacterial infections cause huge losses to aquaculture globally, and increased antibiotic resistance means that alternative methods of reducing mortality from bacterial diseases are required. We compared the resistance of Juvenile olive flounders, Paralichthys olivaceus, to Streptococcus iniae between those reared in biofloc and seawater conditions for ten months. Experimental fish were challenged with S. iniae at concentrations of 0, 3.36 × 10⁶, 3.36 × 10⁷, 3.36 × 10⁸, and 3.36 × 10⁹ colony forming units (CFU)/g fish for 96 h to evaluate the difference in S. iniae susceptibility of flounders reared in biofloc and seawater. The 96 h lethal concentration 50% (LC₅₀) of fish injected with S. iniae was 2.41 × 10⁹ CFU/g fish in biofloc and 1.51 × 10⁸ CFU/g fish in seawater. Hematological parameters such as hemoglobin and hematocrit significantly decreased when fish were challenged by S. iniae. Plasma components such as calcium, glucose, cholesterol, total protein, GOT, GPT, and ALP were significantly altered by S. iniae infection and acetylcholinesterase activity was significantly inhibited. These results indicate that S. iniae infection affects the survival rates, hematological parameters, and neurotransmitter levels of flounders reared in biofloc and seawater, and that S. iniae susceptibility was higher in flounders reared in seawater than those reared in biofloc.

Effects of Supplement of Marichromatium gracile YL28 on Water Quality and Microbial Structures in Shrimp Mariculture Ecosystems

The elevated NH₃-N and NO₂-N pollution problems in mariculture have raised concerns because they pose threats to animal health and coastal and offshore environments. Supplement of Marichromatium gracile YL28 (YL28) into polluted shrimp rearing water and sediment significantly decreased ammonia and nitrite concentrations, showing that YL28 functioned as a novel safe marine probiotic in the shrimp culture industry. The diversity of aquatic bacteria in the shrimp mariculture ecosystems was studied by sequencing the V4 region of 16S rRNA genes, with respect to additions of YL28 at the low and high concentrations. It was revealed by 16S rRNA sequencing analysis that Proteobacteria, Planctomycete and Bacteroidetes dominated the community (>80% of operational taxonomic units (OTUs)). Up to 41.6% of the predominant bacterial members were placed in the classes Gammaproteobacteria (14%), Deltaproteobacteria (14%), Planctomycetacia (8%) and Alphaproteobacteria (5.6%) while 40% of OTUs belonged to unclassified ones or others, indicating that the considerable bacterial populations were novel in our shrimp mariculture. Bacterial communities were similar between YL28 supplements and control groups (without addition of YL28) revealed by the β-diversity using PCoA, demonstrating that the additions of YL28 did not disturb the microbiota in shrimp mariculture ecosystems. Instead, the addition of YL28 increased the relative abundance of ammonia-oxidizing and denitrifying bacteria. The quantitative PCR analysis further showed that key genes including nifH and amoA involved in nitrification and nitrate or nitrite reduction significantly increased with YL28 supplementation (p < 0.05). The supplement of YL28 decreased the relative abundance of potential pathogen Vibrio. Together, our studies showed that supplement of YL28 improved the water quality by increasing the relative abundance of ammonia-oxidizing and denitrifying bacteria while the microbial community structure persisted in shrimp mariculture ecosystems.

Metagenomics in bioflocs and their effects on gut microbiome and immune responses in Pacific white shrimp

Biofloc systems generate and accumulate microbial aggregates known as bioflocs. The presence of bioflocs has been shown to change gut bacterial diversity and stimulate innate immunity in shrimp. The microbial niche of bioflocs may therefore have the potential to drive shifts in the shrimp gut microbiota associated with stimulation of innate immunity. We performed shotgun metagenomic analysis and 16S rRNA-based amplicon sequencing to characterize complex bacterial members in bioflocs and the shrimp digestive tract, respectively. Moreover, we determined whether biofloc-grown shrimp with discrete gut microbiomes had an elevation in local immune-related gene expression and systemic immune activities. Our findings demonstrated that the bacterial community in bioflocs changed dynamically during Pacific white shrimp cultivation. Metagenomic analysis revealed that Vibrio comprised 90% of the biofloc population, while Pseualteromonas, Photobacterium, Shewanella, Alteromonas, Bacillus, Lactobacillus, Acinetobacter, Clostridium, Marinifilum, and Pseudomonas were also detected. In the digestive tract, biofloc-grown shrimp maintained the presence of commensal bacteria including Vibrio, Photobacterium, Shewanella, Granulosicoccus, and Ruegeria similar to control shrimp. However, Vibrio and Photobacterium were significantly enriched and declined, respectively, in biofloc-grown shrimp. The presence of bioflocs upregulated immune-related genes encoding serine proteinase and prophenoloxidase in digestive organs which are routinely exposed to gut microbiota. Biofloc-grown shrimp also demonstrated a significant increase in systemic immune status. As a result, the survival rate of biofloc-grown shrimp was substantially higher than that of the control shrimp. Our findings suggested that the high relative abundance of vibrios in bioflocs enriched the number of vibrios in the digestive tract of biofloc-grown shrimp. This shift in gut microbiota composition may be partially responsible for local upregulation of immune-related gene expression in digestive organs and systemic promotion of immune status in circulating hemolymph.

Mannanoligosaccharides as a Carbon Source in Biofloc Boost Dietary Plant Protein and Water Quality, Growth, Immunity and Aeromonas hydrophila Resistance in Nile Tilapia (Oreochromis niloticus)

Simple Summary

Biofloc technology (BFT), offers some potential advantages for improvements in water quality and growth of farmed fish reared in recirculation systems. One practical disadvantage of implementing a BFT system to culture fish is the need to add organic carbon to maintain a C:N ratio above 10. The present study evaluated the effect of using mannan oligosaccharides as a carbon source in a biofloc system with cultivated tilapia. MOS resulted in increased lactic acid bacterial count in the water and the intestinal tract, modulated immune response and resistance against Aeromonus hydrophila and improved the survival and growth of reared Nile tilapia (Oreochromis niloticus L.)

Abstract

The aim of the present study was to evaluate mannan oligosaccharides (MOS) or glycerol (GLY) as a carbon source on biofloc systems of Nile tilapia (O. niloticus) juveniles. Fish (n = 750) were reared in open flow (Controls) or biofloc systems (B-GLY and B-MOS) fed with a plant or fish protein source over a period of twelve weeks. Total ammonia nitrogen and nitrate decreased in the biofloc groups, while biofloc volume increased in B-MOS. Compared to the controls, B-MOS and B-GLY exhibited higher weight gain and improved feed conversion, irrespectively of the diet. Serum level of C-reactive protein was reduced, while IgM and lysozyme activity was higher in the B-MOS fish, compared to other groups. Intestinal Bacillus spp. count was increased, whereas Vibrio, Aeromonas and Pseudomonas spp. counts decreased in B-MOS reared groups, compared to the other groups. The proinflammatory cytokine (IL-8 and IFN-γ) transcript expression was upregulated in B-MOS more than B-GLY reared groups. Compared to the controls, the virulence of Aeromonas hydrophila was decreased in the B-MOS and B-GLY groups. The results indicate several benefits of using MOS as a carbon source in a biofloc Nile tilapia system; a cost benefit analysis is required to assess the economic viability of this.

The Application of Single-Cell Ingredients in Aquaculture Feeds—A Review

Single-cell ingredients (SCI) are a relatively broad class of materials that encompasses bacterial, fungal (yeast), microalgal-derived products or the combination of all three microbial groups into microbial bioflocs and aggregates. In this review we focus on those dried and processed single-cell organisms used as potential ingredients for aqua-feeds where the microorganisms are considered non-viable and are used primarily to provide protein, lipids or specific nutritional components. Among the SCI, there is a generalised dichotomy in terms of their use as either single-cell protein (SCP) resources or single-cell oil (SCO) resources, with SCO products being those oleaginous products containing 200 g/kg or more of lipids, whereas those products considered as SCP resources tend to contain more than 300 g/kg of protein (on a dry basis). Both SCP and SCO are now widely being used as protein/amino acid sources, omega-3 sources and sources of bioactive molecules in the diets of several species, with the current range of both these ingredient groups being considerable and growing. However, the different array of products becoming available in the market, how they are produced and processed has also resulted in different nutritional qualities in those products. In assessing this variation among the products and the application of the various types of SCI, we have taken the approach of evaluating their use against a set of standardised evaluation criteria based around key nutritional response parameters and how these criteria have been applied against salmonids, shrimp, tilapia and marine fish species.

Biofloc-Based Enhanced Survival of Litopenaeus vannamei Upon AHPND-Causing Vibrio parahaemolyticus Challenge Is Partially Mediated by Reduced Expression of Its Virulence Genes

The biofloc system is a relatively new aquaculture technology that offers practical solution to maintain culture water quality by recycling nutrients and improves the health status and resistance of shrimps against microbial infection, yet the mode of action involved remains unclear. This study aimed to unravel the underlying mechanism behind the protective effect of a biofloc system using Litopenaeus vannamei and acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus M0904 strain as a host-pathogen model. The results showed that a biofloc system maintained at a C/N ratio of 15, improves the water quality and contributes to the nutrition of cultured animals as bioflocs might serve as an additional protein source. Furthermore, the study demonstrated that the biofloc system enhances the survival of L. vannamei upon challenge with a V. parahaemolyticus AHPND strain. Remarkably, the results highlight that in the biofloc system, AHPND-causing V. parahaemolyticus possibly switch from free-living virulent planktonic phenotype to a non-virulent biofilm phenotype, as demonstrated by a decreased transcription of flagella-related motility genes (flaA, CheR, and fliS), Pir toxin (PirB^VP), and AHPND plasmid genes (ORF14) and increased expression of the phenotype switching marker AlkPhoX gene in both in vitro and in vivo conditions. Taken together, results suggest that biofloc steer phenotype switching, contributing to the decreased virulence of V. parahaemolyticus AHPND strain toward shrimp postlarvae. This information reinforces our understanding about AHPND in a biofloc setting and opens the possibility to combat AHPND not only by trying to eliminate the AHPND-causing V. parahaemolyticus from the system but rather to steer the phenotypic switch.

Effects of dietary Lactobacillus plantarum (KC426951) in biofloc and stagnant-renewal culture systems on growth performance, mucosal parameters, and serum innate responses of Nile tilapia Oreochromis niloticus

Effects of dietary Lactobacillus plantarum (KC426951) on growth and innate responses of Nile tilapia Oreochromis niloticus were evaluated in biofloc technology system and stagnant-renewal culture system (SRCS). The 90-day-long experiment contained four treatments: SRCS without probiotic (T1), SRCS with probiotic (T2), biofloc without probiotic (T3), and biofloc with probiotic (T4). The administration dose of probiotic was 2 × 10⁸ CFU kg^-1 diet. At the end of experiment, the mean final weights, specific growth rates, feed conversion ratios, and total biomass were significantly (P < 0.05) better in BFT treatments, with no significant effect of probiotic on these parameters in both culture systems. Meanwhile, skin mucosal parameters including total protein (TP), lysozyme (LYZ), alkaline phosphatase (ALP), and protease (PRO) activity were significantly enhanced following probiotic supplementation. T4 treatment displayed a significantly higher LYZ and ALP activity in mucus versus other treatments. Also, serum alternative complement activity was significantly heightened in probiotic-supplemented fish. Superoxide dismutase activity in T4 was detected higher than that of SRCS groups. The results of the current study demonstrated the enhancement of some mucosal and serum innate responses of Nile tilapia in both culture systems upon L. plantarum (KC426951) supplementation.

Environmental rearing conditions are key determinants of changes in immune gene expression patterns in shrimp midgut

The super-intensive BioFloc Technology (BFT) system has been highlighted as a promising eco-friendly alternative to the traditional shrimp rearing systems. To gain insight into the impact of environmental rearing conditions on shrimp intestinal immunity, we assessed the expression profile of key immunological genes in the midgut of Litopenaeus vannamei shrimp reared in two contrasting culture systems: the indoor super-intensive BFT and the outdoor intensive Green-Water System (GWS). From the 30 analyzed genes, the expression levels of 25 genes were higher in the midgut of shrimp reared in BFT than in GWS. The main functional categories represented in BFT-shrimp were the prophenoloxidase-activating system, immune signaling, antimicrobial peptides, and RNA interference pathway. Comparatively, only the RNAi pathway gene Dicer-1 (LvDcr1) was more expressed in animals from the GWS group. However, despite the differences in gene expression, the total midgut bacterial abundance was similar between the experimental groups. Altogether, our results suggest that the microbial-rich environment offered by the BFT system can be acting as an immunostimulant by altering the immune expression profile of the midgut. The gene expression level found in GWS animals could be related to the chronic presence of the IMNV in the Brazilian Northeast. Knowing the effects of environmental stress factors on the intestinal immune defenses can provide an in-depth understanding of the relationship between cultivated shrimp and the major pathogens affecting the shrimp industry.

Effects of Carbon/Nitrogen Ratio on Growth, Intestinal Microbiota and Metabolome of Shrimp (Litopenaeus vannamei)

Increasing the C/N ratio of input feed has been reported as a practical approach for improving water quality and enhancing shrimp growth through changing the bacterial community of rearing water. However, little is known about the effects of different C/N ratios of feed input on the intestinal microbiota and metabolome of shrimp. In the present study, the effects of three different C/N ratio levels (CN6, CN10, and CN15) maintained by adding sucrose on the growth, intestinal microbiota and metabolome of Litopenaeus vannamei, and bioflocs formation were investigated after 17 days of feeding. The results indicated that higher C/N ratio (10 and 15), especially CN15, of feed input significantly enhance the length and weight of shrimp individuals accompanied by a significant accumulation of bioflocs, compared to that of CN6. The increase of C/N ratio input decreased the α-diversity of the intestinal microbiota and changed the microbial community structure through increasing the relative abundance of Actinobacteria, Rhodobacteraceae (mainly consist of Roseobacter and Paracoccus groups), Alteromonadaceae, and inhibiting the growth of Cyanobacteria, certain Rhodobacteraceae, Mycoplasmataceae and Vibrio. The change of microbial community caused by increasing C/N ratio input was closely associated with various bioactive metabolites of flavonoids, benzenoids, prenol lipids, and indole derivatives, which are benefit for shrimp growth either as an antimicrobial agent or as a nutrient component. Overall, this study demonstrated that manipulating high C/N ratio of feed input helps to the growth of shrimp through increasing the relative abundance of potential beneficial bacteria and the accumulation of various bioactive metabolites to suppress the growth of detrimental bacteria.

Poly-β-hydroxybutyrate (PHB) in bioflocs alters intestinal microbial community structure, immune-related gene expression and early Cyprinid herpesvirus 2 replication in gibel carp (Carassius auratus gibelio)

The aquaculture system based on biofloc technology (BFT) showed positive effects on prevention of Cyprinid herpesvirus 2 (CyHV-2) infection in gibel carp (Carassius auratus gibelio), which is detrimental to health and causes seriously economic losses to aquaculture. However, the enhancement mechanism of BFT regarding immunity and disease resistance of cultured species is scarce. Poly-β-hydroxybutyrate (PHB) has been proved as one of bioactive compounds in bioflocs. In this study, two groups (4% PHB supplementation diets and control with basal diets) with 30-day feeding were set to study the effect of PHB supplementation on immune-related gene expression by qRT-PCR, time-course CyHV-2 replication in vivo by qPCR and intestinal microbiota by illumine high-throughput sequencing. PHB supplementation significantly up-regulated transcriptional levels of eight immune-related genes, decreased cumulative mortality of gibel carp and early CyHV-2 replication in spleen in vivo (P < 0.05). Additionally, PHB changed the microbial structure but not diversity, and significantly increased beneficial bacteria such as Bacillus sp. KEGG pathway analysis by PICRUSt demonstrated that oral administration of PHB up-regulated abundances of genes responsible for seven pathways and down-regulated genes in eleven pathways. Histological structures of foregut, mindgut and hindgut were also affected. Our findings suggested that profitable effects of PHB on immunity and disease resistance might be gut microbiota-related, and regulated through pathways of enzymes secretion, replication and repair, and host immune system. This study will provide new insights into understanding the enhancing mechanism of BFT on immunity and disease resistance of cultured animals, and developing prebiotics/probiotics-based immunotherapies to improve animal health and disease resistance.

Effects on hematological parameters, antioxidant and immune responses, AChE, and stress indicators of olive flounders, Paralichthys olivaceus, raised in bio-floc and seawater challenged by Edwardsiella tarda

Studies on the resistance of fish raised in bio-floc systems against bacterial infection are limited. We aimed to evaluate the changes in hematological parameters, antioxidant and immune responses, stress indicators, and acetylcholinesterase (AChE) in olive flounder, Paralichthys olivaceus, raised in bio-floc and seawater for 10 months and, then, infected with Edwardsiella tarda at concentrations of 0 (control), 6.61 × 10⁴, 6.61 × 10⁵, 6.61 × 10⁶, and 6.61 × 10⁷ CFU/g fish for 7 days. The lethal concentration 50% was 4.32 × 10⁷ in bio-floc and 3.11 × 10⁶ in seawater. Hematological parameters were significantly decreased by E. tarda challenge, and plasma components were significantly changed. The superoxide dismutase, catalase, and glutathione-S-transferase activities, as antioxidant responses, were significantly increased after infection, whereas the reduced glutathione level was significantly decreased. The lysozyme activity was significantly increased and the AChE level was significantly decreased after infection. Cortisol and HSP 70, as stress indicators, were also significantly increased. The results indicate that E. tarda infection affected various physiological factors in P. olivaceus. Additionally, P. olivaceus raised in seawater were more susceptible to E. tarda infection than those raised in bio-floc.

Toxic effects of waterborne nitrite exposure on antioxidant responses, acetylcholinesterase inhibition, and immune responses in olive flounders, Paralichthys olivaceus, reared in bio-floc and seawater

Paralichthys olivaceus (mean weight, 280.1 ± 10.5 g; mean length, 28.37 ± 2.3 cm) was reared in bio-floc and seawater for 6 months to determine the toxic effects of waterborne nitrite exposure (0, 25, 50, 100, and 200 mg/L) for 1 week, compared to those observed with bio-floc and seawater only. The effects on antioxidant activity, immune responses, and acetylcholinesterase activity were measured. Following nitrite exposure, superoxide dismutase activity in the liver and gills was significantly elevated and catalase activity was significantly increased, except for in the gills of P. olivaceus reared in bio-floc. Further, glutathione S-transferase activity was significantly elevated in the liver and gills, and glutathione was significantly lower. Meanwhile, acetylcholinesterase activity in the liver and gills was significantly inhibited and plasma lysozyme activity and immunoglobulin M were considerably elevated.

Bioflocs substituted fishmeal feed stimulates immune response and protects shrimp from Vibrio parahaemolyticus infection

Fishmeal is the main source of protein in the shrimp feed industry and is normally derived from trash fish. As such, the production of fishmeal has an adverse effect on the marine environment by taking away small and juvenile fish, leading to depletion of marine species. There is a need for alternative sources of protein which will substitute fishmeal in the aquaculture industry. This study evaluated the components and nutritional efficacy of bioflocs, which were used to substitute fishmeal protein. The effect of bioflocs diets on growth performance, survival rate, and immune response in shrimp compared to normal fishmeal feed were determined. Bioflocs were harvested from the shrimp ponds (C:N ratio >12:1) at Shrimp Village, Chaiya district, Surat Thani, Thailand. The total protein in bioflocs was about 48% and the total lipid was about 5% (dried weight) and the percentages of essential amino acids (EAA) and fatty acids (EFA) in bioflocs were similar to those of fishmeal feed. Shrimp fed with the different dietary bioflocs feed regimens [% to replace fishmeal; 0% (B0), 25% (B25), 50% (B50), 75% (B75), and 100% (B100)] for 42 days revealed that all growth parameters were almost similar to those of the control shrimp (shrimp fed with normal fishmeal, B0) including final body weight, weight gain, specific growth rate, and feed conversion ratio. Remarkably, the survival rates, the levels of immune parameters, and expression of immune genes (proPO-I, PEN-4 and dicer) were significantly higher in bioflocs fed shrimp, especially in B25 and B50 shrimp. Moreover, B25 and B50 bioflocs fed shrimp showed notably increased survival rates following Vibrio parahaemolyticus (V. parahaemolyticus) infection. In conclusion, the present study demonstrates that shrimp survival and immunity are enhanced by biofiocs substituted fishmeal. Significantly, the bioflocs diets activated the immune response to prevent V. parahaemolyticus infection.

Performance and microbial community analysis of Combined Denitrification and Biofloc Technology (CDBFT) system treating nitrogen-rich aquaculture wastewater

This study proposed two novel Combined Denitrification and Biofloc Technology (CDBFT) systems (one under blue LED light (L1) and the other without light (C1), each containing a denitrification (DE) reactor and a biofloc-based reactor) for the enhanced total nitrogen (TN) removal. Long-term operation (110 days) suggested that simultaneous nitrification and denitrification was achieved in both C1 and L1. Significantly higher total nitrogen removal efficiency (TNRE) was observed in L1-CDBFT (92.2%) than C1-CDBFT (87.5%, P < 0.05; after day 14). Further 24-hour nitrogen transformation test showed the boosted nitrate removal of L1-BFT than C1-BFT. High-throughput sequencing analysis revealed that phyla Rotifera and Nematoda which were indispensable for aquatic animal larviculture, were only found in L1-BFT. Nevertheless, CDBFT effluent from both systems was suitable for tilapia culture based on water quality, biofloc characteristics and tilapia survival rates. Overall, this study highlights the significance of developing CDBFT for TN removal especially under lights.

Effect of Carbon to Nitrogen Ratio on Water Quality and Community Structure Evolution in Suspended Growth Bioreactors through Biofloc Technology

Application of biofloc technology could effectively treat wastewater. However, the effect of influent carbon to nitrogen ratio (C/N ratio) on water quality and microbial community structure evolution in suspended growth bioreactors (SGBRs) through biofloc technology is still unclear. Here, we show that the total ammonia nitrogen (TAN) and nitrite nitrogen in the effluent of the C/N 10 treatment was significantly higher than that in the C/N 15, C/N 20 and C/N 25 treatments (p < 0.05). Higher TAN removal efficiency was obtained in treatments of C/N 15, C/N 20 and C/N 25, and there was no accumulation of nitrite nitrogen and nitrate nitrogen. Increasing the C/N ratio strengthened the elimination ability of total phosphorus and chemical oxygen demand (COD). The concentrations of TAN and COD first dropped to the lowest level and then increased slightly within one cycle in all treatments. The accumulation of biomass in the reactors increased with the increasing C/N ratio, indicating that a higher C/N ratio was conducive to microbial proliferation. The 16S rRNA sequencing revealed that the microbial community diversity in SGBRs was significantly higher than that in the natural wastewater (P0). The predominant phylum were Proteobacteria, Bacteroidetes and Verrucomicrobia, but Saccharibacteria occupied a dominant position in the late period of the experiment. Pathogens, such as Aeromonas, Acidovorax, Flavobacterium, and Malikia were significantly decreased after high C/N ratio simulative wastewater treating natural wastewater in the reactors. In summary, the water quality and biomass concentrations in SGBRs can be improved under the conditions of influent C/N ratio, equal to or greater than 15.

The Role of Bacillus amyloliquefaciens on Litopenaeus vannamei During the Maturation of a Biofloc System

Biofloc technology is a sustainable aquaculture production system which uses microorganisms to maintain water quality and to increase productivity. In this system, probiotics can enhance the positive effects of bioflocs on the cultured species. The objective of this research is to study the role of the probiotic bacterium Bacillus amyloliquefaciens during the formation of a biofloc system for the culture of Litopenaeus vannamei. Two doses of probiotic were assayed and applied directly to the water. The experiment was developed in nine tanks distributed as follows: Three control tanks with no probiotic, three tanks with a probiotic dose of 103 cfu/mL, and three tanks with a dose of 104 cfu/mL. Water quality, microbial activity, growth parameters and the immune system state of shrimps were monitored throughout the maturation process. The results indicate a positive effect upon the shrimp immune system throughout the study period, where specifically there was an increase in granular hemocytes in the shrimp hemolymph. During the immature biofloc phase, granular hemocytes were 5% higher in tanks supplemented with the probiotic. During the mature biofloc phase, granular hemocytes were 7% higher in those same tanks. During the maturation of the biofloc, environmental conditions are more unfavorable for shrimp growth, due to the accumulation of nitrites. So, the effect of the probiotic is especially important during this stage when the shrimp are stressed and are more vulnerable to diseases. However, the effects on microbial activity, water quality and Litopenaeus vannamei growth did not increase the benefits of the biofloc system.

Carbohydrate sources deferentially influence growth performances, microbial dynamics and immunomodulation in Pacific white shrimp (Litopenaeus vannamei) under biofloc system

This study aims to evaluate the influence of different carbohydrate sources on water quality, growth performance and immunomodulation in pacific white shrimp and to find an alternate for molasses in biofloc system. The experiment consists of 8 biofloc treatments with different carbon sources, C1 (maida flour), C2 (wheat flour), C3 (gram flour), C4 (millet flour), C5 (rice flour), C6 (corn flour), C7 (molasses), C8 (multigrain flour) and un-supplemented control C0 was conducted in 200 L tank system for 120 days. Shrimp juveniles of average weight 1 g were stocked at the rate of 300 nos/m³. Shrimp reared in C8, C7 and C4 treatments had similar growth, survival rate, and disease resistance and were significantly higher (P < 0.05) than other treatments including control. Immune parameters like total hemocyte count (THC) and prophenoloxidase (ProPO) activity showed significantly higher (P < 0.05) levels in biofloc treatment groups. The genes targeting the proPO cascade (PX, BGBP) and antioxidant defense systems (SOD, MnSOD, CAT) revealed significant upregulation in the transcript levels indicating an enhancement in the immune-regulatory functions in the BFT groups. The results suggest that millets and multigrain flour can effectively replace molasses as the carbohydrate source for biofloc system and the biofloc system offers higher growth, survival, and immunomodulation than control.

Effects of Bacillus aryabhattai TBRC8450 on vibriosis resistance and immune enhancement in Pacific white shrimp, Litopenaeus vannamei

The use of probiotics in aquaculture is a practical alternative to promote animal health and disease prevention. Meanwhile, this practice can also reduce the use of prophylactic antibiotics. The purpose of this study was to identify candidate probiotics that could control pathogen populations in host's gastrointestinal (GI) tract and stimulate host immunity in shrimp aquaculture. Bacillus aryabhattai TBRC8450, a bacterial strain isolated from the environment in a shrimp farm, has an antimicrobial activity against many pathogenic strains of Vibrio harveyi and V. parahaemolyticus. Supplementation of B. aryabhattai to Pacific white shrimp (Litopenaeus vannamei) not only decreased the abundance of Vibrio populations, but also shifted the bacterial community in the shrimp GI tract. We found that supplementation of B. aryabhattai triggered shrimp innate immunity and antioxidant activities. mRNA expression of genes encoding microbial peptides and antioxidant enzymes, including C-type lectin, penaeidin-3, heat shock protein 60, thioredoxin, and ferritin, was significantly upregulated in the hepatopancreas of shrimp fed B. aryabhattai. Furthermore, phenoloxidase activity in the hemocytes and the total antioxidant activity in the plasma were increased, indicating enhanced immune and antioxidant responses at the systemic level. In contrast, supplementation of B. aryabhattai had no effect on the total hemocyte count and superoxide dismutase activity in the plasma and hepatopancreas. Importantly, a pathogen challenge test using V. harveyi 1562 showed a significant increase in survival rates of shrimp fed B. aryabhattai compared to the control group. Our findings suggest that B. aryabhattai TBRC8450 can likely be used as a probiotic to reduce the population of V. harveyi in the shrimp GI tract and to enhance shrimp innate immunity and antioxidant capacity for vibriosis resistance in shrimp aquaculture.

Carbon: Nitrogen (C:N) ratio level variation influences microbial community of the system and growth as well as immunity of shrimp (Litopenaeus vannamei) in biofloc based culture system

Biofloc technology (BFT) is a novel modern aquaculture farming technique used to reduce toxic nitrogen concentration, act as in situ food source and eradicate pollutants using carbon and therefore to control C:N ratio in an aquaculture system. In this study, effect of different C:N ratios of a biofloc based system on water quality such as the level of Total ammonia nitrogen (TAN) nitrite-nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N) were explored. Further, the growth and immunity status of shrimp L. vannamei under the influence of different C:N ratios were evaluated. Two of the C:N ratios (15 and 20) could significantly (P < 0.05) reduce TAN, NO₂-N and NO₃-N levels (0.456 ± 0.01, 0.145 ± 0.09, and 0.102 ± 0.02 ppm) compared to control (1.45 ± 0.1, 0.749 ± 0.14 and 0.675 ± 0.16 ppm). Large variations in the frequency distribution of operational taxonomic units (OTUs) for the bacterial community in water with different C:N ration (BFT) and control were observed. Vibrios often considered as opportunistic pathogens, where the most dominant bacterial flora of water in control (79%) and C:N5 (37%) group. In C:N10, Thauera (62%) was most represented genus. Similarly, Attheyaceae (56%), followed by Peridiniaceae (30%) were the most dominant groups in C:N15 treatment. The diversity of bacterial flora was more spread in C:N20 treatments with Psychrobacter (26%), Proteobacteria (25%) and Peridiniaceae (20%) as the major groups. The trend of Vibrio dominance decreased with the increase in C:N ratios and thus confirming the dominance of heterotrophic bacteria in high C:N ratio groups. Upon challenge with pathogens, shrimps from C:N10, C:N15 and C:N20 groups showed significantly higher survival (P < 0.05) compared to the C:N5 and control group. Similarly, better growth rate was also observed in BFT tanks compared to control both during the culture and at harvest. Comparatively higher expression of four immune-related genes (ras-related nuclear gene (RAN), serine proteinase gene (SP), prophenoloxidase activating enzyme (PPAE), and crustin were observed in different C:N ratio ponds than control and these were in increasing trend with the C:N ratio. Gene expression analysis showed that the transcripts of those immune genes were significantly increased among all C:N treatments than that of control. Overall, these findings demonstrated that with optimum C:N ratio, BFT can be used to optimize the bacterial community composition for both optimal water quality and optimal shrimp health. This study thus indicates the possibility of obtaining better performance of L. vannamei culture with proper adjustment of C:N ratio in a biofloc based system.

Exploring the Impact of the Biofloc Rearing System and an Oral WSSV Challenge on the Intestinal Bacteriome of Litopenaeus vannamei

We provide a global overview of the intestinal bacteriome of Litopenaeus vannamei in two rearing systems and after an oral challenge by the White spot syndrome virus (WSSV). By using a high-throughput 16S rRNA gene sequencing technology, we identified and compared the composition and abundance of bacterial communities from the midgut of shrimp reared in the super-intensive biofloc technology (BFT) and clear seawater system (CWS). The predominant bacterial group belonged to the phylum Proteobacteria, followed by the phyla Bacteroidetes, Actinobacteria, and Firmicutes. Within Proteobacteria, the family Vibrionaceae, which includes opportunistic shrimp pathogens, was more abundant in CWS than in BFT-reared shrimp. Whereas the families Rhodobacteraceae and Enterobacteriaceae accounted for almost 20% of the bacterial communities of shrimp cultured in BFT, they corresponded to less than 3% in CWS-reared animals. Interestingly, the WSSV challenge dramatically changed the bacterial communities in terms of composition and abundance in comparison to its related unchallenged group. Proteobacteria remained the dominant phylum. Vibrionaceae was the most affected in BFT-reared shrimp (from 11.35 to 20.80%). By contrast, in CWS-reared animals the abundance of this family decreased from 68.23 to 23.38%. Our results provide new evidence on the influence of both abiotic and biotic factors on the gut bacteriome of aquatic species of commercial interest.

Biofloc technology application in aquaculture to support sustainable development goals

Biofloc technology (BFT) application offers benefits in improving aquaculture production that could contribute to the achievement of sustainable development goals. This technology could result in higher productivity with less impact to the environment. Furthermore, biofloc systems may be developed and performed in integration with other food production, thus promoting productive integrated systems, aiming at producing more food and feed from the same area of land with fewer input. The biofloc technology is still in its infant stage. A lot more research is needed to optimise the system (in relation to operational parameters) e.g. in relation to nutrient recycling, MAMP production, immunological effects. In addition research findings will need to be communicated to farmers as the implementation of biofloc technology will require upgrading their skills.

Effects of stocking density of the white shrimp Litopenaeus vannamei (Boone) on immunities, antioxidant status, and resistance against Vibrio harveyi in a biofloc system

Determining optimum stocking density of the white shrimp Litopenaeus vannamei (Boone) is a big concern for shrimp farmers. However, few studies have assessed the influence of stocking density on the antioxidant status, immunology, digestive enzyme activities, and growth performance of white shrimp in biofloc systems. In this study, these parameters of white shrimp in a biofloc system were compared at three stocking densities: 300 orgs m^-3 as low stocking density (LD), 400 orgs m^-3 as medium stocking density (MD), and 500 orgs m^-3 as high stocking density (HD). The feed conversion ratio in the LD group was significantly lower than that in the MD and HD groups (P < 0.05), and the ultimate individual weight in the LD group was significantly higher than that in the other two groups (P < 0.05). The antioxidant status and immunology parameters, including complement 3, complement 4, lysozyme, superoxide dismutase, glutathione peroxidase and malondialdehyde were all depressed in the HD groups. Furthermore, activities of the digestive enzymes, amylase, trypsin, and lipase were lower in the MD and HD groups than that in the LD group. The highest relative percentage survival was observed in the LD group 10 days after challenge with the pathogen Vibrio harveyi. Results of this study indicated that the immune status and welfare of white shrimp can be seriously impaired in the HD condition (i.e., ≥500 m^-3) in biofloc systems. These findings can be used to determine suitable stocking densities in the white shrimp farming industry using the biofloc system.

Effects of carbon sources and plant protein levels in a biofloc system on growth performance, and the immune and antioxidant status of Nile tilapia (Oreochromis niloticus)

The efficacy of different biofloc treatments (BFTs) to compensate for a reduction in dietary protein level under zero-water exchange systems was studied during a 10 weeks experiment, assessing the effect on water quality, growth, immune and antioxidant status of Nile tilapia (Oreochromis niloticus) fingerlings. Six groups were established and fed the same plant-based feed containing 20 or 30% crude protein: two groups in clear water conditions with no added carbon source, two biofloc groups given a wheat milling by-product (WMB) as additional carbon source and two biofloc groups given rice bran (RB). The results showed that biofloc volume was higher when WMB was used as carbon source. The highest growth performance were obtained with the biofloc system and the higher dietary protein level. Fish fed 20% crude protein and stocked in WMB biofloc significantly outperformed the fish fed 30% crude protein and stocked in clear water. Significant improvements in hematocrit, white blood cells, lymphocytes, plasma proteins, and humoral (immunoglobulin, lysozyme, myeloperoxidase and ACH₅₀) and cellular (phagocytosis activity and respiratory burst) immune parameters were observed in all BFT fish. BFT also increased superoxide dismutase and catalase activities. Moreover, the fish fed 20% dietary protein and reared in both biofloc conditions showed equal or superior levels of the immunological criteria to fish fed 30% protein in clear water conditions. In conclusion, using WMB as carbon source could make up for a reduction in dietary protein levels of 10% and improve growth performance, and the immune and antioxidant status of O. niloticus.

Bacterial community characterization of water and intestine of the shrimp Litopenaeus stylirostris in a biofloc system

BACKGROUND

Biofloc technology (BFT), a rearing method with little or no water exchange, is gaining popularity in aquaculture. In the water column, such systems develop conglomerates of microbes, algae and protozoa, together with detritus and dead organic particles. The intensive microbial community presents in these systems can be used as a pond water quality treatment system, and the microbial protein can serve as a feed additive. The current problem with BFT is the difficulty of controlling its bacterial community composition for both optimal water quality and optimal shrimp health. The main objective of the present study was to investigate microbial diversity of samples obtained from different culture environments (Biofloc technology and clear seawater) as well as from the intestines of shrimp reared in both environments through high-throughput sequencing technology.

RESULTS

Analyses of the bacterial community identified in water from BFT and "clear seawater" (CW) systems (control) containing the shrimp Litopenaeus stylirostris revealed large differences in the frequency distribution of operational taxonomic units (OTUs). Four out of the five most dominant bacterial communities were different in both culture methods. Bacteria found in great abundance in BFT have two principal characteristics: the need for an organic substrate or nitrogen sources to grow and the capacity to attach to surfaces and co-aggregate. A correlation was found between bacteria groups and physicochemical and biological parameters measured in rearing tanks. Moreover, rearing-water bacterial communities influenced the microbiota of shrimp. Indeed, the biofloc environment modified the shrimp intestine microbiota, as the low level (27 %) of similarity between intestinal bacterial communities from the two treatments.

CONCLUSION

This study provides the first information describing the complex biofloc microbial community, which can help to understand the environment-microbiota-host relationship in this rearing system.

From microbes to fish the next revolution in food production

Increasing global population and the consequent increase in demand for food are not a new story. Agroindustrial activities such as livestock help meet this demand. Aquaculture arose decades ago and revolutionized the agroindustrial activity as a significant food generator. However, like livestock, aquaculture is based on finite resources and has been accused of being unsustainable. Abandoning aquaculture is not an option considering the food, foreign exchange, and employment it generates, and therefore must be reinvented. Among the many alternatives suggested to make aquaculture more sustainable, microorganisms have been highlighted as a direct food source for cultured fish and crustaceans, a strategy that promises to revolutionize aquaculture by eliminating waste. Considering waste, as part of a cycle, it can increase stock densities and reduce emissions of contaminants and operational costs.

Growth performance and immunological and antioxidant status of Chinese shrimp, Fennerpenaeus chinensis reared in bio-floc culture system using probiotics

Chinese shrimp Fennerpenaeus chinensis (mean length 1.86 ± 0.15 cm, and weight 137.4 ± 12.7 mg) were reared in the different concentrations of bio-floc (control, 60, 80, 100, 120, and 140%) for 90 days. The growth rate was significantly increased over 100% bio-floc concentrations. In the immunological parameters, the gene expression of proPO and lysozyme was considerably increased over 120% bio-floc concentrations. The gene expression of SP was notably elevated at 140% bio-floc concentration. In the antioxidant enzymes, the activity of SOD was considerably decreased over 80% bio-floc concentrations. A notable decline in the activity of CAT was observed over 120% bio-floc concentrations. The results indicate that rearing of Chinese shrimp in bio-floc system can induce the increase of growth performance, enhancement of immune responses, and reduction of oxidative stress.

Rearing effect of biofloc on antioxidant and antimicrobial transcriptional response in Litopenaeus stylirostris shrimp facing an experimental sub-lethal hydrogen peroxide stress

This study compares the antioxidant and antimicrobial transcriptional expression of blue shrimps reared according to two different systems, BioFloc Technology (BFT) and Clear sea Water (CW) and their differential responses when facing an experimental sublethal hydrogen peroxide stress. After 30 days of rearing, juvenile shrimps were exposed to H2O2 stress at a concentration of 30 ppm during 6 h. The oxidative stress caused by H2O2 was examined in the digestive glands of the shrimp, in which antioxidant enzyme (AOE) and antimicrobial peptide (AMP) gene expression were analysed by quantitative real-time PCR. Results showed that rearing conditions did not affect the expression of genes encoding AOEs or AMPs. However, H2O2 stress induced a differential response in expression between shrimps from the two rearing treatments (BFT and CW). Comparative analysis of the expression profiles indicates that catalase transcripts were significantly upregulated by H2O2 stress for BFT shrimps while no change was observed for CW shrimps. In contrast, H2O2 caused down-regulation of superoxide dismutase and glutathione transferase transcripts and of the three AMP transcripts studied (penaeidin 2 and 3, and crustin) for CW shrimps, while no effect was observed on BFT shrimp transcript levels. These results suggested that BFT shrimps maintained antioxidant and AMP responses after stress and therefore can effectively protect their cells against oxidative stress, while CW shrimp immune competence seems to decrease after stress.