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

A Review on Biofloc System Technology, History, Types, and Future Economical Perceptions in Aquaculture

Given the scarcity of water and land resources, coupled with the competitive nature of aquaculture, the long-term viability of this industry will depend on strategies for vertical development. This involves enhancing production environments, increasing productivity, and advancing aquaculture technologies. The use of biofloc technology offers a potential solution to mitigate the adverse environmental impacts and the heavy reliance on fishmeal in the aquaculture sector. This method is designed to effectively assimilate inorganic nitrogen found in aquaculture wastewater, thereby enhancing water quality. Additionally, this process produces microbial protein, which can serve as a viable supplemental feed for aquatic animals. Furthermore, this technique has the potential to reduce the feed conversion ratio, thereby lowering overall production costs. This article provides an overview of the evolving field of biofloc system technology within aquaculture. In this study, we will examine the historical development and various types of biofloc systems, as well as the factors that influence their effectiveness. Finally, we will explore the economic potential of implementing biofloc systems in aquaculture.

Utilization of Sugarcane Bagasse (Saccharum officinarum Linn.) as a Carbon Source in Biofloc System of Vaname Shrimp Litopenaeus vannamei

<b>Background and Objective:</b> Vaname shrimp (<i>Litopenaeus vannamei</i>) is one of the main economic commodities in aquaculture in the world. Biofloc is a cultivation technology that effectively improves the growth and health status of vaname shrimp. This research aimed to analyze the use of bagasse as a carbon source in the biofloc system for white shrimp cultivation. <b>Materials and Methods:</b> The shrimp used were 18 g/individual shrimp obtained from the Bone Marine and Fisheries Polytechnic Pond. Sugarcane bagasse processed from sugar factory waste was dried in an oven at 60°C and ground using a flouring machine. The research treatments included biofloc application where sugarcane bagasse played a role as a carbon source (L), biofloc application where wheat flour's role was as a carbon source (T) and control or no biofloc application (K). <b>Results:</b> This research showed that sugarcane bagasse could be used as a carbon source for white shrimp biofloc cultivation where the growth value tended to be the same as wheat flour. Total hemolytic count (THC) and shrimp survival in sugarcane bagasse biofloc were as good as wheat flour biofloc. Sugarcane bagasse biofloc had the same ability as wheat flour biofloc in reducing ammonia levels in the rearing media. Sugarcane bagasse biofloc had the same ability as wheat flour biofloc in reducing ammonia levels in the rearing media. The application of bagasse had no effect on temperature, pH, dissolved oxygen and salinity of the rearing media because this treatment was in the optimal range for the growth of vaname shrimp. <b>Conclusion:</b> Sugarcane bagasse has the potential to be a carbon source in biofloc systems because it could improve growth, health status, survival and water quality.

Comparative Transcriptome Analysis of the Response to Vibrio parahaemolyticus and Low-Salinity Stress in the Swimming Crab Portunus trituberculatus

Vibrio parahaemolyticus is one of the main pathogenic bacteria of Portunus trituberculatus and causes mass mortality of P. trituberculatus in aquaculture. In addition, low-salinity stimulation makes P. trituberculatus more susceptible to V. parahaemolyticus infections. In order to elucidate the molecular mechanism of resistance to V. parahaemolyticus in P. trituberculatus, comparative transcriptomic analysis of blood cells stimulated by low salinity and V. parahaemolyticus was carried out in this study. Transcriptome sequencing of low-salinity stress and pathogen infection at different time points was completed using Illumina sequencing technology. A total of 5827, 6432, 5362 and 1784 differentially expressed genes (DEGs) involved in pathways related to ion transport and immunoregulation were found under low-salinity stress at 12, 24, 48 and 72 h compared with the control at 0 h. In contrast, 4854, 4814, 5535 and 6051 DEGs, which were significantly enriched in Toll and IMD signaling pathways, were found at 12, 24, 48 and 72 h compared with the control at 0 h under V. parahaemolyticus infection. Among them, 952 DEGs were shared in the two treatment groups, which were mainly involved in apoptosis and Hippo signaling pathway. Cluster analysis screened 103 genes that were differentially expressed in two factors that were negatively correlated, including immunoglobulin, leukocyte receptor cluster family, scavenger receptor, macroglobulin and other innate-immune-related genes. These results provide data support for the analysis of the mechanisms of immunity to V. parahaemolyticus under low-salinity stress in P. trituberculatus and help to elucidate the molecular mechanisms by which environmental factors affect immunity.

Gut bacterial consortium enriched in a biofloc system protects shrimp against Vibrio parahaemolyticus infection

BACKGROUND

Shrimp cultured in a biofloc system (BFS) have a lower disease incidence than those farmed in a water exchange system (WES). Although a number of studies have reported that the gut bacterial community induced by BFS is highly associated with shrimp disease resistance, the causal relationship remains unknown. Here, the promotive roles of gut bacterial community induced by BFS in pathogenic Vibrio infection resistance and its potential micro-ecological and physiological mechanisms were investigated by gut bacterial consortium transplantation and synthetic community (SynCom) construction.

RESULTS

The BFS induced a more stable and resistant gut bacterial community, and significantly enriched some beneficial bacterial taxa, such as Paracoccus, Ruegeria, Microbacterium, Demequina, and Tenacibaculum. Transplantation of a gut bacterial consortium from BFS shrimp (EnrichBFS) greatly enhanced the stability of the bacterial community and resistance against pathogenic V. parahaemolyticus infection in WES shrimp, while transplantation of a gut bacterial consortium from WES shrimp significantly disrupted the bacterial community and increased pathogen susceptibility in both WES and BFS shrimp. The addition of EnrichBFS in shrimp postlarvae also improved the pathogen resistance through increasing the relative abundances of beneficial bacterial taxa and stability of bacterial community. The corresponding strains of five beneficial bacterial taxa enriched in BFS shrimp were isolated to construct a SynComBFS. The addition of SynComBFS could not only suppress disease development, but also improve shrimp growth, boost the digestive and immune activities, and restore health in diseased shrimp. Furthermore, the strains of SynComBFS well colonized shrimp gut to maintain a high stability of bacterial community.

CONCLUSIONS

Our study reveals an important role for native microbiota in protecting shrimp from bacterial pathogens and provides a micro-ecological regulation strategy towards the development of probiotics to ameliorate aquatic animal diseases. Video Abstract.

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.

Screening of bioflocculant and cellulase-producing bacteria strains for biofloc culture systems with fiber-rich carbon source

The biofloc technology (BFT) system has been widely applied in the shrimp and fish culture industry for its advantages in water-saving, growth improvement, and water quality purification. However, The BFT system usually takes a long time to establish, and the extra carbon source input increases the maintenance cost of the system. In this study, we aimed to develop a low-cost and high-efficient BFT system for Litopenaeus vannamei by applying bacteria that could promote the formation of BFT and utilize cheap carbon sources. Three bioflocculant-producing bacteria strains (M13, M15, and M17) have been screened from a cellulolytic strain collection. All three strains have been identified as Bacillus spp. and can use sugarcane bagasse (SB) as a carbon source, which is a cheap byproduct of the sucrose industry in the tropic area of China. Compared to sucrose, the addition of SB and the three strains could improve the biofloc formation rate, biofloc size distribution, ammonia removal rate, and the growth performance of the shrimps. These results suggest that the bioflocculant and cellulase-producing bacteria strains could promote the biofloc formation and the growth of shrimps by using SB as an economic substitute carbon source in the BFT shrimp culture system.

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.

Dietary inclusion of rambutan (Nephelium lappaceum L.) seed to Nile tilapia (Oreochromis niloticus) reared in biofloc system: Impacts on growth, immunity, and immune-antioxidant gene expression

An eight-week feeding trial was carried out to determine the effects of rambutan seed (RS) as a feed additive on the growth, skin mucus, serum immune parameters, and gene expression of Nile tilapia (Oreochromis niloticus) raised under a biofloc system. Nile tilapia fingerlings (14.77 ± 0.80 g fish^-1) were fed five experimental diets containing 0, 5, 10, 20, and 40 g kg^-1 of RS, corresponding to five treatments (RS0, RS5, RS10, RS20, and RS40) with three replications per treatment. The results showed that fish consuming the RS10 and RS20 diets presented a substantial (P < 0.05) improvement in specific growth rate (SGR), weight gain (WG), and feed conversion ratio (FCR) after eight weeks. The highest values were recorded in the RS10 diet; however, there were no significant (P > 0.05) differences exhibited in the fish survival rates between treatments. The RS supplementation diets demonstrated greater immunological parameters, particularly skin mucus and serum immune responses (P < 0.05), than that of the control after eight the eight-week feeding trial. The highest level was seen in fish fed the RS10; followed by the RS20, RS40 (P > 0.05), and RS5 diets. Regarding gene expressions, IL1, IL8, LBP, GSTa, and GSR genes were significantly up-regulated in fish provided the RS10 diet in comparison to the control and other supplemented diets (P < 0.05). However, no significant up-regulation was found in these genes among the RS0, RS5, RS20, and RS40 diets, with the exception of the GPX gene. Similarly, up-regulation of IL-8, LBP, GSTa, GPX, and GSR were noted in fish fed the RS10 diet (P < 0.05). Notably, no significant differences were evident in these genes among the RS5, RS20, and RS40 diets. In conclusion, fish fed RS10 (10 g kg^-1) significantly enhanced growth, skin mucus, serum immunities, and immune-antioxidants related gene expressions of Nile tilapia raised under biofloc system.

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.

Cellular and molecular immune response and production performance of Indian white shrimp Penaeus indicus (H. Milne-Edwards, 1837), reared in a biofloc-based system with different protein levels of feed

The present study focuses on the immunity and growth of Penaeus indicus fed with varying protein levels (25%, 30%, and 35%) in a biofloc based rearing system. A 120 days growth trial was carried out using juvenile Penaeus indicus (0.71 ± 0.01) with dietary protein level, 25% (LP), 30% (MP), and 35% (HP), and a control diet-fed with 35% acted as control group resulting in 4 treatments each with four replicates and were randomly assigned 16 tank units (7500 L each). A combination of different carbon sources (molasses, wheat flour, and rice bran in 2:1:1 ratio), yeast and a probiotic (Bacillus sp.) consortium were used for the development of biofloc. At the end of the trial, the growth parameters of shrimps viz., initial weight, feed conversion ratio (FCR), and daily growth coefficient (DGC) were computed. The results indicated that shrimp fed with medium (30%) protein (MP) diet recorded significantly (P < 0.05) improved growth performance compared to high protein fed group (35%) and low protein (25%) fed group (LP) in a biofloc system and control group (35%). The immunological parameters such as hemagglutination activity (HA) assay, serum protein, lysozyme, phenol oxidase (PO), and inhibition of superoxide dismutase (SOD) activity were observed in serum, plasma, and hemocyte lysate supernatant (HLS). The HA activity, PO activity in plasma was found to be higher in high protein fed animals, whereas medium protein resulted in enhanced PO activity in serum. Similarly, lysozyme and SOD were inhibited well in high protein fed animals compared to the low protein fed group. The vital immune genes's mRNA profiling showed a potential rise in the expressional pattern in MP and HP treatments compared to LP and control. BGBP (beta-1,3-glucan binding protein) and hemocyanin mRNA transcript levels were highly upregulated in the HP (5 fold) and moderately expressed in MP (2 fold) and LP (1-2 fold). The transcripts of peroxinectin, antimicrobial peptides like crustin showed significant upregulation in HP followed by in MP and LP and control. Likewise, other immune genes, such as SOD, prophenoloxidase (proPO), showed a similar trend in a marginal way, indicating immunomodulation in the biofloc groups. This study suggested that biofloc with high protein (35%) supplementation can substantially enhance the immune response of shrimps, although medium protein level (30%) is optimum for improving the survival, growth, and in turn economic return in Indian white shrimp.

Bioaugmentation of biofloc system with enzymatic bacterial strains for high health and production performance of Penaeus indicus

The beneficial effects of two probiotic bacterial strains Marinilactibacillus piezotolerans and Novosphingobium sp. during the culture of Indian white shrimp, Penaeus indicus, under biofloc and clear water system were evaluated. The experimental variation were CW1 (M. piezotolerans in clear water), BFT1 (biofloc + M. piezotolerans), CW2 (Novosphingobium sp. in clear water), BFT2 (biofloc + Novosphingobium sp.) and control (without bacterial strains and biofloc). Growth and survival considerably increased in probiotic bio-augmented treatments. Probiotic incorporation significantly improved water quality, especially ammonia reduction. Microbiota analysis from gut samples taken from different treatments revealed varied microbial population structure among clear water culture, biofloc culture and control. Proteobacteria and Firmicutes were the top phyla observed in the treatments which were significantly higher in bio-augmented systems than the control. Vibrio genera were predominantly observed in control and clear water system compared to that of biofloc systems. Immune genes were significantly altered in response to probiotic gut microbial supplementation than the control. Higher gene expression profile of important immune genes was observed in the biofloc reared shrimps. Expression of digestive enzyme related genes such as trypsin, chymotrypsin, cathepsin L, cathepsin B and alpha amylase were also upregulated significantly in probiotic supplementation especially in the biofloc treatments. Proteomic analysis of hepatopancreas of shrimps from different treatments was carried out by using 2D gel electrophoresis and MALDI-TOF analysis. The proteins were mostly related to growth and stress tolerance. Eukaryotic initiation factor 4E binding protein was expressed in all the groups and it was high in biofloc treated animals followed by animals treated solely with probiotics compared to those of control groups. The results concludes that biofloc already proved as an effective culture method for healthy shrimp production and supplementation of probiotic bacterial strains registered additional benefit for growth, survival, microbial, immunological status of P, indicus culture.

Effects of graded levels of starch on the non-specific immune responses, antioxidant capacities and intestinal health in Chinese mitten crab, Eriocheir inensis

A 9-week feeding trial was conducted to investigate the effects of graded levels of dietary starch (12%, 17%, 22%, 27% and 32%) on growth, non-specific immune responses, antioxidant capacities, immunity genes expression levels and pathogen resistance in Chinese mitten crab, Eriocheir inensis (initial body weight: 10.5 ± 0.5 g). Results showed that the highest weight gain rate of crabs was obtained in group containing 22% dietary starch. The highest activity of acid phosphatase, phenoloxidase and lysozyme in blood was found in crabs fed with 22-27% dietary starch. Additionally, 17%-27% dietary starch significantly increased the activities of superoxide dismutase and glutathione peroxidase, reduced malondinaldehyde content and then increased the total antioxidant capacities in hepatopancreas of crabs. The highest activity of alanine aminotransferase and aspartate aminotransferase was found in crabs fed with 32% dietary starch, indicating that excess starch had a negative effect on the liver function of crabs. With the dietary starch level increased, the transcription factors gene expression of the pro-inflammatory factors were significantly up-regulated, and the highest ILF2, IL-16, Relish and ADAM10 was found in crabs fed with dietary 32% starch, which may potentially promote the inflammatory response in intestines. Moreover, with the dietary starch increased, the activity of phenoloxidase and lysozyme, as well as the gene expression of crustin, were all increased in crabs after challenge against Citrobacter freundii, which demonstrated that additional dietary starch could provide immune-protection and help crabs improve their resistance against pathogens. In conclusion, these results suggest that adequate dietary starch can increase growth, enhance innate immune responses and promote disease resistance, reduce oxidative stress and inflammatory response in E. inensis. Taken together, 22-27% dietary starch (25.9-30.8% dietary carbohydrate) was suggested as a digestible energy source in crabs feed.

Bio-augmentation of heterotrophic bacteria in biofloc system improves growth, survival, and immunity of Indian white shrimp Penaeus indicus

Effect of bio-augmentation of Bacillus spp in biofloc on growth, survival and immunity in Indian white shrimp Penaeus indicus was evaluated. Nine Bacillus strains were isolated and screened individually as well as in the form of a consortia. To maintain a C:N ratio of 12:1 a blend of carbohydrate sources was used. Bio-augmentation with bacterial consortium and Virgibacillus sp. produced improved growth and immunity. Shrimp survival ranged from 80 to 95% among treatments. Production was higher (35%) in the biofloc tanks with an average body weight (ABW) of 10.89 ± 1.2 g. On evaluating the immune responses, it was found that trypsin significantly (P < 0.05) enhanced Prophenoloxidase (PO) activity in Lysinibacillus, Bacillus cereus, Bacillus licheniformis and Bacillus subtilis bio-augmented groups. Laminarin induced PO activity was observed in groups supplemented with Oceanobacillus sp., Bacillus sp.and Bacillus megaterium. The lysozyme (LZ) activity was significantly (P < 0.05) higher in B. cereus and Microbial Consortia (MC), while other treatments were less effective. Total hemocyte count (THC) significantly (P < 0.05) increased in all treatment groups compared to the control. Hyaline hemocyte (HH) count was significantly (P < 0.05) higher in the control group (14.43%). Semi granular hemocytes (SGH) was higher in groups treated with Lysinibacillus, Bacillus sp., B. licheniformis and B. subtilis. The granular hemocyte (GH) count was significantly (P < 0.05) higher in Virgibacillus sp., B. cereus, B.megaterium and Oceanobacillus sp. The biofloc alone (BF), treated and augmented with B. megaterium significantly (P < 0.05) increased phagocytic activity. Highly significant phagocytic index (PI) was observed in bio-augmented groups, BF and MC. The relative expression levels of immune genes were found to be significantly up-regulated in shrimps grown in bio-augmented groups. Enhanced immunological parameters implies that bio-augmentation of biofloc with Bacillus spp. improved immunity in shrimps. Hence, bio-augmentation of probiotics in biofloc may be useful in improving culture conditions to produce P. indicus.