Immunological responses of customised probiotics-fed marron, Cherax tenuimanus, (Smith 1912) when challenged with Vibrio mimicus

Probiotics, Prebiotics, and Synbiotics Utilization in Crayfish Aquaculture and Factors Affecting Gut Microbiota

Aquaculture is affected by numerous factors that may cause various health threats that have to be controlled by the most environmentally friendly approaches. In this context, prebiotics, probiotics, and synbiotics are frequently incorporated into organisms' feeding rations to ameliorate the health status of the host's intestine, enhancing its functionality and physiological performance, and to confront increasing antimicrobial resistance. The first step in this direction is the understanding of the complex microbiome system of the organism in order to administer the optimal supplement, in the best concentration, and in the correct way. In the present review, pre-, pro-, and synbiotics as aquaculture additives, together with the factors affecting gut microbiome in crayfish, are discussed, combined with their future prospective outcomes. Probiotics constitute non-pathogenic bacteria, mainly focused on organisms' energy production and efficient immune response; prebiotics constitute fiber indigestible by the host organism, which promote the preferred gastrointestinal tract microorganisms' growth and activity towards the optimum balance between the gastrointestinal and immune system's microbiota; whereas synbiotics constitute their combination as a blend. Among pro-, pre-, and synbiotics' multiple benefits are boosted immunity, increased resistance towards pathogens, and overall welfare promotion. Furthermore, we reviewed the intestinal microbiota abundance and composition, which are found to be influenced by a plethora of factors, including the organism's developmental stage, infection by pathogens, diet, environmental conditions, culture methods, and exposure to toxins. Intestinal microbial communities in crayfish exhibit high plasticity, with infections leading to reduced diversity and abundance. The addition of synbiotic supplementation seems to provide better results than probiotics and prebiotics separately; however, there are still conflicting results regarding the optimal concentration.

From waste to feed: Microbial fermented abalone waste improves the digestibility, gut health, and immunity in marron, Cherax cainii

New aquafeed ingredients produced by a circular economy approach are the opportunity for sustainable and resilient aquaculture. In the light of this approach, the mixture of abalone waste and Sargassum spp (9:1) fermented by Saccharomyces cereviceae and Lactobacillus casei (Yakult®) (FMAS) were used to replace 0% (FMAS0), 25% (FMAS-25), 50% (FMAS-50), 75% (FMAS-75), and 100% (FMAS-100) of fishmeal (FM) protein in marron, Cherax cainii diet. The marron was fed these diets in triplicate for 90 days. Growth, feed utilization and protein efficiency ratio were unchanged in marron-fed all test diets. Improvement in apparent protein digestibility was aligned with an increase in the size and number of B-cells in the hepatopancreas. Most of the immune responses, except for haemocyte clotting time, hyaline cells and neutral red retention time (NRR time) were unchanged by 42- and 90-days feeding trials compared to those of the control group. 90 days post-feeding marron with FMAS25 showed a lower haemocyte clotting time than the post 42 days feeding marron with the same diet. Hyaline cells increased in marron fed FMAS75 for 90 days compared to marron fed the same diet for 42 days. The challenge test involved injecting marron with Vibrio mimicus resulted in a 100% survival rate after 96 h of exposure. During the challenge test, phagocytosis activity in 24 and 48-h post-challenged marron fed FMAS75 decreased which recovered after 96 h post-challenge. Marron fed FMAS50 also recorded a significantly higher proportion of granular cells after 24 h and NRR time at 96 h compared with that of other treatments. Given the above indicators of bio-growth, feed efficiency and immune responses, total replacement of FM protein of marron practical feed with FMAS are considered feasible and optimum to maintain health status and resistance to disease.

Zeolite mediated processing of nitrogenous waste in the rearing environment influences gut and sediment microbial community in freshwater crayfish (Cherax cainii) culture

Zeolite is known to uptake toxic metals and filter nitrogenous waste from aquaculture effluents. The present study aimed to investigate the impacts of zeolite in three different applications namely, dietary zeolite (DZ), suspended zeolite (SZ) in the water column, and a combination of both (DZSZ) relative to unexposed freshwater crayfish, marron (control). At the end of the 56-days trial, the impact was assessed in terms of characterization of microbial communities in the culture environment and the intestine of marron. Alongside the microbial communities, the innate immune response of marron was also evaluated. The 16S rRNA data showed that marrons exposed to the suspended zeolite had a significant increase of bacterial diversity in the gut, including the restoration of marron core operational taxonomic units (OTUs), relative to other forms of exposures (DZ, DZSZ) and the control. Suspended zeolite alone also increased the number of unshared OTUs and genera, and improved predicted metabolic functions for the biosynthesis and digestion of proteins, amino acids, fatty acids, and hormones. In the tank sediment, the shift of microbial communities was connected more strongly with the time of experiment than the type of zeolite exposure. In the second case, only control marron had a different microbial ordination in terms of rare taxa present in the community. Nevertheless, the modulation in the gut environment was found more prominent in DZ, relative to modulation in the tank sediments. The taxa-environment correlation identified Rhodoferax as the most potential bacteria in removing nitrogenous waste from the rearing environment. Further analysis showed that SZ resulted in the upregulation of genes associated with the innate immune response of marron. Overall results suggest that SZ can be used to enrich microbial communities in the gut and tank sediments and better immune performance of marron.

A Mixture of Manganese, Silica and Phosphorus Supplementation Alters the Plankton Density, Species Diversity, Gut Microbiota and Improved the Health Status of Cultured Marron (Cherax cainii, Austin and Ryan, 2002)

Trace element supplementation to the freshwater environment can influence the plankton density and species diversity, contributing to the nutrition of aquaculture species, especially during the juvenile stage. An experiment was conducted under laboratory conditions to evaluate the effects of supplementing different mixtures of manganese, silica and phosphorus on the plankton density and species diversity and their impact on cultured juvenile marron (Cherax cainii, Austin and Ryan, 2002). Manganese, silica and phosphorus in concentrations of 0.0024, 0.41, 0.05 mg*L^-1; 0.0041, 0.82, 0.12 mg*L^-1; and 0.0058, 1.26, 0.25 mg*L^-1 respectively termed as low, medium and high were supplemented to tank water containing a phytoplankton density of 3.77 ± 0.16 × 10⁶ cells*L^-1 and 292.9 ± 17.6 individuals*L^-1 of zooplankton, and plankton growth was observed every 24 h for 6 days. Afterwards, a 3-month trial was conducted studying the effects of these trace element concentrations and resulting plankton densities on marron growth, survival, moulting, gut microbiota and health indices. Silica supplementation at high concentration increased the diatom abundance, silica and phosphorus supplementation at higher concentration that resulted in a significant increase in plankton density and species diversity, leading to improved marron health indices than the control and the tanks receiving a low concentration. Marron-specific growth rate, weight gain and dissolved copper concentration in haemolymph were significantly higher in tanks with higher supplementation and higher plankton density. Marron survival, moult interval and total haemocyte count were not affected by the supplementation. Marron gut microbiota at higher trace element concentration supplementation showed a significant increase in abundance of phosphate solubilizing bacteria.

Lactobacillus plantarum in black soldier fly (Hermetica illucens) meal modulates gut health and immunity of freshwater crayfish (Cherax cainii)

Probiotic supplements are being used to improve the growth and immune performance of aquaculture species over the last couple of decades. In recent times, black soldier fly (BSF) is considered as one of the promising sources of alternative protein to fishmeal protein in aqua-diets. Since the freshwater crayfish, marron (Cherax cainii), a Western Australian's native and iconic freshwater crayfish species, grows fairly slow under commercial farming environment, this study was aimed to investigate the supplemental effect of BSF and BSF with probiotic bacteria Lactobacillus plantarum (BSFLP) on overall health and immune performance of marron after 56 days of feeding under laboratory conditions. The post-trial data revealed insignificant influences of any diets on growth performance, however, both BSF and BSFLP based diets significantly improved some haemolymph parameters and gut health of marron. High throughput sequence data revealed that both BSF and BSFLP diets significantly improved the diversity of microbial communities including some beneficial bacteria for crustaceans in the hindgut of marron. Further analysis showed that both BSF and BSFLP diets upregulated the expression of some genes in the gut tissue and haemocytes associated with the innate immune response of marron at 48 h post injection. The up-regulation of some immune genes in BSFLP diet group was found significantly linked to OTU abundance for Lactobacillus. The findings of this study could be helpful for improving overall health status of marron.

Biological filters regulate water quality, modulate health status, immune indices and gut microbiota of freshwater crayfish, marron (Cherax cainii, Austin, 2002)

Water quality has significant impacts on the health and immune responses of aquaculture species. This study aimed to analyse and compare the effects of two biological filters namely, gravel and, Bio-Ball with a recently developed filter called Water-cleanser on regulation of water quality parameters, health and immune response of marron reared in plastic tanks for 60 days. Results showed that addition of Bio-Ball significantly (P < 0.05) reduced the concentration of ammonia, nitrate and phosphate while Water-cleanser showed the ability to reduce ammonia and nitrate from water in aquaculture tanks. Although the biological filters had no significant effect on marron growth but inclusion of Bio-Ball and Water-cleanser positively influenced the biochemical composition of tail muscle and some haemolymph parameters of marron. The next generation sequence data demonstrated higher bacterial diversity in the hindgut of marron with Water-cleanser, followed by Bio-Ball and gravel, respectively. In addition, the predicted metabolic pathways revealed a significantly higher bacterial activity and gene function correlated to metabolism and biosynthesis of protein, energy and secondary metabolites in Bio-Ball and Water-cleanser. Bio-Ball and Water-cleanser were also associated with up-regulation of innate immune responsive genes of marron gut. Overall, Bio-Ball and Water-cleanser proved to have higher water remediation and immune response modulation capabilities, and therefore could be used as preferred filters for growth of beneficial bacteria in crayfish culture.

Lactobacillus acidophilus and L. plantarum improve health status, modulate gut microbiota and innate immune response of marron (Cherax cainii)

This study aimed to investigate the combined effects of two most potent probiotic bacteria Lactobacillus acidophilus and Lactobacillus plantarum on overall health and immune status of freshwater crayfish, marron under laboratory conditions. A total of 36 marron were distributed into six different tanks and two different feeding groups, control and probiotic-fed group. After acclimation, control group was fed with basal diet while probiotic group was fed 109 CFU/mL per kg of bacterial supplemented feed for 60 days. The results showed no significant differences in weight gain, however, probiotic feed significantly enhanced some hemolymph parameters and biochemical composition of tail muscle. Histology data revealed better hepatopancreas health and higher microvilli counts in the marron gut fed probiotic diet. The probiotic bacteria triggered significant shift of microbial communities at different taxa level, mostly those reported as beneficial for crayfish. The probiotic diet also enriched the metabolic functions and genes associated with innate immune response of crayfish. Further correlation analysis revealed significant association of some taxa with increased activity for hemolymph and immune genes. Therefore, dietary Lactobacillus supplementation can modulate the overall health and immunity as well as gut microbial composition and interaction network between gut microbiota and immune system in crayfish.

Marked variations in gut microbiota and some innate immune responses of fresh water crayfish, marron (Cherax cainii, Austin 2002) fed dietary supplementation of Clostridium butyricum

This study aimed to investigate the effects of Clostridium butyricum as a dietary probiotic supplement in fishmeal based diet on growth, gut microbiota and immune performance of marron (Cherax cainii). Marron were randomly distributed into two different treatment groups, control and probiotic fed group. After 42 days of feeding trial, the results revealed a significant (P < 0.05) increase in growth due to increase in number of moults in marron fed probiotics. The probiotic diet also significantly enhanced the total haemocyte counts (THC), lysozyme activity in the haemolymph and protein content of the tail muscle in marron. Compared to control, the 16S rRNA sequences data demonstrated an enrichment of bacterial diversity in the probiotic fed marron where significant increase of Clostridium abundance was observed. The abundance for crayfish pathogen Vibrio and Aeromonas were found to be significantly reduced post feeding with probiotic diet. Predicted metabolic pathway revealed an increased activity for the metabolism and absorption of carbohydrate, degradation of amino acid, fatty acid and toxic compounds, and biosynthesis of secondary metabolites. C. butyricum supplementation also significantly modulated the expression level of immune-responsive genes of marron post challenged with Vibrio mimicus. The overall results suggest that C. butyricum could be used as dietary probiotic supplement in marron aquaculture.

The effect of a multi-strain probiotic on growth performance, non-specific immune response, and intestinal health of juvenile turbot, Scophthalmus maximus L

Probiotic is well known because of its health benefit on the host, including improve growth, treat disease, and enhance immunity. Currently, probiotic has been widely used in aquaculture. However, there is little information about the effect of probiotic on turbot. Therefore, an effort was made to explore the effect of a multi-strain probiotic on growth performance, non-specific immune response, and intestinal health of juvenile turbot, Scophthalmus maximus L. One hundred eighty juvenile turbot (20.04 ± 0.23 g) were randomly divided into three groups (T0, T1, T2), and fed diet were formulated to contain 0%, 1%, and 5% multi-strain probiotic, respectively. Sixty days after the feeding experiment, the growth performance, body composition, enzyme activities, and intestinal microorganism of turbot were analyzed. T2 and T1 showed better growth performance and significant higher (P < 0.05) enzyme activities than T0 (except lysozyme). Moreover, the IV (intestinal villus), IW (intestinal wall), and GC (goblet cell) were well modulated in probiotic treatments. Furthermore, Lactobacillus was found colonized in the intestine of the group fed with 5% multi-strain probiotic. These results suggested adding dietary multi-strain probiotic could positively affect for turbot aquaculture.

Dietary supplementation of black soldier fly (Hermetica illucens) meal modulates gut microbiota, innate immune response and health status of marron (Cherax cainii, Austin 2002) fed poultry-by-product and fishmeal based diets

The present study aimed to evaluate the dietary supplementary effects of black soldier fly (Hermetia illucens) (BSF) meal on the bacterial communities in the distal gut, immune response and growth of freshwater crayfish, marron (Cherax cainii) fed poultry-by-product meal (PBM) as an alternative protein source to fish meal (FM). A total of 64 marron were randomly distributed into 16 different tanks with a density of four marron per tank. After acclimation, a 60-days feeding trial was conducted on marron fed isonitrogenouts and isocalorific diets containing protein source from FM, PBM, and a combination of FM + BSF and PBM + BSF. At the end of the trial, weight gain and growth of marron were found independent of any dietary treatment, however, the two diets supplemented with BSF significantly (P < 0.05) enhanced haemolymph osmolality, lysozyme activity, total haemocyte counts, and protein and energy contents in the tail muscle. In addition, the analysis of microbiota and its predicted metabolic pathways via 16s rRNA revealed a significantly (P < 0.05) higher bacterial activity and gene function correlated to biosynthesis of protein, energy and secondary metabolites in PBM + BSF than other dietary groups. Diets FM + BSF and PBM + BSF were seen to be associated with an up-regulation of cytokine genes in the intestinal tissue of marron. Overall, PBM + BSF diet proved to be a superior diet in terms of improved health status, gut microbiota and up-regulated expression of cytokine genes for marron culture.

Effects of different dietary protein sources on the immunological and physiological responses of marron, Cherax cainii (Austin and Ryan, 2002) and its susceptibility to high temperature exposure

A two phased feeding trial was conducted to evaluate the effects of alternative protein sources on the immunophysiological responses of marron. During the phase I, marron were fed with five alternative protein supplemented diets for 90 days, while in phase II, the same marron were exposed to elevated temperature (30 °C) and their immunophysiological responses were investigated post exposure. Five isoproteic (crude protein 30%) and isoenergetic diets were prepared by containing fishmeal, poultry by-product meal, feather meal, lupin meal, and meat and bone meal as the main protein source. A hundred and fifty juvenile marron (Cherax cainii) of the average weight 9.09 ± 0.21 g were randomly distributed into 15 tanks (three replicates per feeding treatments). In the Phase I, general immune response parameters, such as, total haemocyte count (THC), proportion of hyaline cells, neutral red retention time (NRRT), phagocytic rate (PR), heamolymph bacteraemia, and condition indices of marron were investigated. The highest (P < 0.05) THC among dietary protein sources was obtained in marron fed with PbM at the end of experiment. Marron fed with FeM protein sources resulted in the highest survival rate followed by PbM fed group. Longer microvilli length (3.83 ± 0.18 μm) was demonstrated in marron fed with PbM diet. Diets containing FM and PbM protein sources revealed significantly (P < 0.05) lower number of microvilli/group than diets containing FeM and LM. The results demonstrated that different dietary protein sources in the marron diets did not detect significant (P > 0.05) change of the condition indices throughout the experiment period, however highest Hiw and Hid was recorded in marron fed with PBM at day 45. The PR of marron fed dietary protein from PbM did not change significantly after temperature exposure. Increased NRRT, PR and haemolymph bacteraemia was observed with dietary feeding of FM at the end of the trial. However, results revealed that PbM could be an alternative protein source for culture of marron as reflected in terms of increased THC, longer microvillus length and improved susceptibility to high temperature exposure. Overall, result could serve as useful baseline data in developing cost effective potential diets for marron aquaculture.

Probiotics, immunostimulants, plant products and oral vaccines, and their role as feed supplements in the control of bacterial fish diseases

There is a rapidly increasing literature pointing to the success of probiotics, immunostimulants, plant products and oral vaccines in immunomodulation, namely stimulation of the innate, cellular and/or humoral immune response, and the control of bacterial fish diseases. Probiotics are regarded as live micro-organisms administered orally and leading to health benefits. However, in contrast with the use in terrestrial animals, a diverse range of micro-organisms have been evaluated in aquaculture with the mode of action often reflecting immunomodulation. Moreover, the need for living cells has been questioned. Also, key subcellular components, including lipopolysaccharides, have been attributed to the beneficial effect in fish. Here, there is a link with immunostimulants, which may also be administered orally. Furthermore, numerous plant products have been reported to have health benefits, namely protection against disease for which stimulation of some immune parameters has been reported. Oral vaccines confer protection against some diseases, although the mode of action is usually linked to humoral rather than the innate and cellular immune responses. This review explores the relationship between probiotics, immunostimulants, plant products and oral vaccines.

Dietary pantothenic acid deficiency and excess depress the growth, intestinal mucosal immune and physical functions by regulating NF-κB, TOR, Nrf2 and MLCK signaling pathways in grass carp (Ctenopharyngodon idella)

This study investigated the effects of dietary pantothenic acid (PA) on the growth, intestinal mucosal immune and physical barrier, and relative mRNA levels of signaling molecules in the intestine of grass carp (Ctenopharyngodon idella). A total of 540 grass carp (253.44 ± 0.69 g) were fed six diets with graded levels of PA (PA1, PA15, PA30, PA45, PA60 and PA75 diets) for 8 weeks. The results indicated that compared with PA deficiency (PA1 diet) and excess (PA75 diet) groups, optimal PA supplementation increased (P < 0.05): (1) percent weight gain (PWG), feed intake and feed efficiency; (2) lysozyme activity, complement 3 content, liver-expressed antimicrobial peptide 2 and hepcidin, interleukin 10, transforming growth factor β1 and inhibitor of κBα mRNA levels in some intestinal segments; (3) activities and mRNA levels of copper/zinc superoxide dismutase, manganese superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferases and glutathione reductase, and NF-E2-related factor 2 (Nrf2) mRNA level in the whole intestine; (4) Claudin b, Claudin 3, Claudin c, Occludin and ZO-1 mRNA levels in some intestinal segments of grass carp. Conversely, optimal PA supplementation decreased (P < 0.05): (1) tumor necrosis factor α, interleukin 1β, interferon γ2, interleukin 8, nuclear factor κB P65 (NF-κB P65), IκB kinase α, IκB kinase β, IκB kinase γ and target of rapamycin (TOR) mRNA expression levels in some intestinal segments; (2) reactive oxygen species, malondialdehyde and protein carbonyl contents, and Kelch-like ECH-associating protein 1a, Kelch-like ECH-associating protein 1b in the intestine; (3) Claudin 12, Claudin 15a and myosin light-chain kinase (MLCK) mRNA levels in some intestinal segments of grass carp. In conclusion, optimum PA promoted growth, intestinal mucosal immune and physical function, as well as regulated mRNA levels of signaling molecules NF-κB P65, TOR, Nrf2 and MLCK in grass carp intestine. Based on the quadratic regression analysis of PWG and intestinal lysozyme activity, the optimal PA levels in grass carp (253.44-745.25 g) were estimated to be 37.73 mg/kg and 41.38 mg/kg diet, respectively.

Isolation and screening of probiotic candidates from marron, Cherax cainii (Austin, 2002) gastrointestinal tract (GIT) and commercial probiotic products for the use in marron culture

Six strains of bacteria including Bacillus mycoides (A10) and Shewanella species (A12) isolated from healthy marron intestine, Bacillus species (PM1), Bacillus subtilis (PM3), Bacillus sp. (PM4) and Bacillus sp. (AQ) from commercial probiotic products were investigated for probiotic potential in marron culture. Antibiotic susceptibility tests indicated PM3 and PM4 were susceptible to all nine antibiotics evaluated. A10, A12 and AQ were resistant to class penicillins, whereas PM1 was resistant to class penicillin and macrolides. All strains were non-pathogenic for marron. Strong inhibition against Vibrio mimicus and Vibrio cholerae non-01 was exhibited by PM4 and PM3. A10 inhibited V. mimicus at 72 h of growth, but not V. cholerae non-01, whereas A12 inhibited V. cholerae non-01 but not V. mimicus, and AQ showed no inhibition activity. A wide range of enzymes were produced by A10 and AQ using the API ZYM test. Protease enzymes were produced by PM3, PM4, AQ and PM1. In order of effectiveness, the following bacteria have probiotic potential: B. subtilis (PM3), Bacillus sp. (PM4) and B. mycoides (A10). Further study is required to determine the bacterium or any combination that gives a multibeneficial effect on marron.

Enhancement of the immune response and protection against Vibrio parahaemolyticus by indigenous probiotic Bacillus strains in mud crab (Scylla paramamosain)

In a previous study, bacterial communities of the intestine in three populations of crabs (wild crabs, pond-raised healthy crabs and diseased crabs) were probed by culture-independent methods. In this study, we examined the intestinal communities of the crabs by bacterial cultivation with a variety of media. A total of 135 bacterial strains were isolated from three populations of mud crabs. The strains were screened for antagonistic activity against Vibrio parahaemolyticus using an agar spot assay. Antagonistic strains were then identified by 16S rRNA gene sequence analysis. Three strains (Bacillus subtilis DCU, Bacillus pumilus BP, Bacillus cereus HL7) with the strongest antagonistic activity were further evaluated for their probiotic characteristics. The results showed that two (BP and DCU) of them were able to survive low pH and high bile concentrations, showed good adherence characteristics and a broad spectrum of antibiotic resistance. The probiotic effects were then tested by feeding juvenile mud crabs (Scylla paramamosain) with foods supplemented with 10(5) CFU/g of BP or DCU for 30 days before being subjected to an immersion challenge with V. parahaemolyticus for 48 h. The treated crabs showed significantly higher expression levels of immune related genes (CAT, proPO and SOD) and activities of respiratory burst than that in controlled groups. Crabs treated with BP and DCU supplemented diets exhibited survival rates of 76.67% and 78.33%, respectively, whereas survival rate was 54.88% in crabs not treated with the probiotics. The data showed that indigenous mud-associated microbiota, such as DCU and BP, have potential application in controlling pathogenic Vibriosis in mud crab aquaculture.

Probiotics in fish and shellfish culture: immunomodulatory and ecophysiological responses

Aquaculture is emerging as one of the most viable and promising enterprises for keeping pace with the surging need for animal protein, providing nutritional and food security to humans, particularly those residing in regions where livestock is relatively scarce. With every step toward intensification of aquaculture practices, there is an increase in the stress level in the animal as well as the environment. Hence, disease outbreak is being increasingly recognized as one of the most important constraints to aquaculture production in many countries, including India. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. The development of non-antibiotic and environmentally friendly agents is one of the key factors for health management in aquaculture. Consequently, with the emerging need for environmentally friendly aquaculture, the use of alternatives to antibiotic growth promoters in fish nutrition is now widely accepted. In recent years, probiotics have taken center stage and are being used as an unconventional approach that has numerous beneficial effects in fish and shellfish culture: improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. As natural products, probiotics have much potential to increase the efficiency and sustainability of aquaculture production. Therefore, comprehensive research to fully characterize the intestinal microbiota of prominent fish species, mechanisms of action of probiotics and their effects on the intestinal ecosystem, immunity, fish health and performance is reasonable. This review highlights the classifications and applications of probiotics in aquaculture. The review also summarizes the advancement and research highlights of the probiotic status and mode of action, which are of great significance from an ecofriendly, sustainable, intensive aquaculture point of view.