Recirculating Aquaculture System Research Articles

Identification of Mycobacterium pseudoshottsii in the Eastern Mediterranean.

Among the numerous pathogenic nontuberculous mycobacteria (NTM), which may cause disease in both poikilothermic and homoeothermic organisms, members of the unique clade Mycobacterium ulcerans/Mycobacterium marinum (MuMC) may cause disease in both fish and humans. Here, we describe the emergence of Mycobacterium pseudoshottsii, one of the four MuMC members, in Israel. For many years, M. marinum was the dominant NTM that was diagnosed in Israel as a fish pathogen. To the best of our knowledge, this is the first isolation and genomic characterization of M. pseudoshottsii infecting edible fish from two different fish species farmed in offshore sea cages in the eastern Mediterranean as well as in a recirculating aquaculture system in Israel. We compared the M. pseudoshottsii whole-genome sequences to all available genomic sequences of MuMC in free, publicly accessible databases. IMPORTANCE Mycobacterium pseudoshottsii was first detected in 1997 in the USA, infecting wild striped bass (Morone saxatilis). Since then, several reports from different countries worldwide have shown its capacity to become established in new regions as well as its pathogenicity to saltwater and euryhaline finfish of different genera. Our phylogenetic analysis revealed that the Mycobacterium ulcerans/Mycobacterium marinum clade (MuMC) is divided into two main branches: one that includes M. marinum and M. pseudoshottsii, and the second, which includes other M. marinum isolates as well as two isolates of M. shottsii. Our results reinforce the proposition that the geographical distribution of M. pseudoshottsii is much more extensive than is commonly believed. The emergence of M. pseudoshottsii in different parts of the world and its pathogenic traits that affect finfish of different genera may be a cause for concern among fish farmers, researchers, and environmental organizations.

Effectiveness of Filter Media Compositions on Water Quality, Growth and Survival Rate of Tilapia (Oreochromis niloticus) Cultured in Recirculation System

Market demand for tilapia (Oreochromis niloticus) is increasing every year. This has encouraged aquaculture companies to apply intensive cultivation systems. However, these applications run the risk of increasing waste and decreasing water quality. One strategy to overcome those problems of water quality is to use recirculation aquaculture system. This study aims to determine the effectiveness of filter media composition on water quality, survival rate, and tilapia growth. The average body weight of the fish used was 3.84 ± 0.05 g per individual. A completely random experiment design with three treatments and three replications were applied. The treatments were combination of several filter media with different compositions, namely A (Dacron + 75% nets + 25% sand), B (Dacron + 50% nets + 50% sand) and C (Dacron + 25% nets + 75% sand).The water quality variables measured were pH, DO, temperature, ammonia, and VTR (Volumetric TAN Removal). The survival rate (SR), relative growth rate (RGR). and total amount feed fed (TFF) of fish were also measured. The results showed that the composition of the filter had a significant effect (P<0.05) between treatment. The best VTR was showed in Treatment C with value 54.65 gm-3d-1.Keywords: Tilapia, recirculation, dacron, nets, sand

Oxidative stress in juvenile tambaqui (Colossoma macropomum) after different periods of air exposure

This study evaluated the response of juvenile Colossoma macropomum to oxidative stress when exposed to air for different periods of time. Fifty-four juveniles weighing 74.8 ± 17.4 g were randomly transferred to nine 30-L tanks in a recirculating aquaculture system and acclimatized to experimental conditions for 15 days. The fish were subsequently fasted for 24 h, after which a group of animals (n = 6) was sampled immediately at the beginning of the experiment to determine baseline levels (without air exposure). Another group (n = 24) was exposed to air for 30 min (30E) and the rest of the fish (n = 24) were exposed to air for 60 min (60E). Oxidative damage and antioxidant defenses were determined immediately after air exposure (IAE; n = 6) and at 1, 24 and 48 h after air exposure (1hAE, 24hAE, and 48hAE; n = 6 animals/per exposure time) by euthanizing fish and immediately removing the gills, liver, kidney, and brain. The interaction between factors (air exposure time x collection time) had an effect on reduced glutathione in the liver (P < 0.0001) and kidney (P = 0.0252). The highest concentrations for reduced glutathione in the gills was for treatment 60E (P = 0.0294), while that for the brain was for treatment 30E (P = 0.0012). Air exposure time had an effect on liver (P < 0.0001) and kidney (P < 0.0001) superoxide dismutase, with the highest values for 60E and 30E, respectively. The interaction between factors had an effect on liver protein levels (P = 0.0029), with the highest value for 30E at 24hAE. Treatment 60E had higher protein degradation in the gills, kidneys and brain than treatment 30E (P < 0.05). Treatment 30E had lower TBARS concentrations in the liver (P = 0.0284) and gills (P = 0.0012), but without damage to the kidney (P = 0.9396) and brain (P = 0.5277). Therefore, air exposure caused changes in antioxidant defenses in the liver, kidney, brain, and gills of C. macropomum juveniles.

Effects of Environmental Enrichment on the Behavior of Octopus vulgaris in a Recirculating Aquaculture System.

Octopus vulgaris is a commercially valuable species. It is overexploited in the natural environment and is considered to be an innovative species for aquaculture. However, large-scale farming is generally designed only based on economic requirements, disregarding any form of enrichment that induces the natural behavior of aquatic species. Although many studies have shown the influence of environmental enrichment on terrestrial vertebrates, fish, and cephalopod mollusks, information on the effect of environmental enrichment on the body patterns of O. vulgaris is limited. Therefore, in this study, we assessed how different environmental conditions (Basic vs. Enriched) affect sub-adults of O. vulgaris kept in recirculation systems, through qualitative-quantitative studies of the main body patterns and their potential application in the commercial production of this species. The results indicated that octopuses kept in the enriched environment showed several body patterns and gained a significantly higher weight than those kept in the basic environment. The body patterns displayed by the individuals kept in the basic environment were similar to those exhibited under situations of hostility and inter/intra-specific conflict. Hence, the environment of octopuses needs to be enriched, especially for the large-scale production of this species.

Comparative estimation of the lysine requirements in two generations of improved strain of Nile tilapia (Oreochromis niloticus) at the grow-out stage

A 3 × 2 factorial experiment was conducted to investigate the effects of dietary lysine on growth performance, body indices, feed intake, feed efficiency, whole body nutrient composition and amino acid deposition in two successive generations (16th and 17th) of GIFT (Oreochromis niloticus). Three diets containing different levels of lysine at 1.16%, 1.56% and 2.41% were prepared for the feeding trial. Triplicate groups of fish with an initial body weight of 155 g were fed to apparent satiation for 10 weeks in a recirculating aquaculture system. Apparent digestibility coefficients (ADC) of dry matter, crude protein, crude lipids, and total carbohydrates were measured in the experimental diets. At the end of the experiment, no interactions between dietary lysine levels in diet and fish generation were observed on all parameters except for the condition factor (CF) and ADC of crude protein. However, dietary lysine level significantly affected the final weight, weight gain, thermal unit growth coefficient (TGC), protein efficiency ratio (PER) and ADC of dry matter regardless of the fish generation. Final weight, weight gain and TGC of fish were the highest in fish fed 2.41% dietary lysine in diet or 6.52% lysine in the protein. PER was the lowest in fish fed 1.16% dietary lysine. The final weight and the body's accumulation of isoleucine, phenylalanine, and alanine were significantly affected by the fish generation, with the 17th generation having the best performance. Increase growth and higher lysine requirement observed in the improved generation (17th) compared to the (16th) generation at grow out phase indicating that genetic improvement may have changed the dietary lysine requirement.

Dietary ribose supplementation improves flesh quality through purine metabolism in gibel carp (Carassius auratus gibelio)

Since the aquaculture industry is currently observing a deterioration in the flesh quality of farmed fish, the use of nutrients as additives to improve the flesh quality of farmed fish species is a viable strategy. The aim of this study was to investigate the effect of dietary D-ribose (RI) on the nutritional value, texture and flavour of gibel carp (Carassius auratus gibelio). Four diets were formulated containing exogenous RI at 4 gradient levels: 0 (Control), 0.15% (0.15RI), 0.30% (0.30RI) and 0.45% (0.45RI). A total of 240 fish (150±0.31g) were randomly distributed into 12 fibreglass tanks (150L per tank). Triplicate tanks were randomly assigned to each diet. The feeding trial was carried out in an indoor recirculating aquaculture system for 60d. After the feeding trial, the muscle and liver of gibel carp were analysed. The results showed that RI supplementation did not result in any negative impact on the growth performance and 0.30RI supplementation significantly increased the whole-body protein content compared to the control group. The contents of collagen and glycogen in muscle were enhanced by RI supplementation. The alterations in the flesh indicated that RI supplementation improved the texture of the flesh in terms of its water-holding capacity and hardness, therefore improving the taste. Dietary RI facilitated the deposition of amino acids and fatty acids in the muscle that contributed to the meaty taste and nutritional value. Furthermore, a combination of metabolomics and expression of key genes in liver and muscle revealed that 0.30RI activated the purine metabolism pathways by supplementing the substrate for nucleotide synthesis and thereby promoting the deposition of flavour substance in flesh. This study offers a new approach for providing healthy, nutritious and flavourful aquatic products.

Microplastics in water, feed and tissues of European seabass reared in a recirculation aquaculture system (RAS)

Plastic particles (PLs) are ubiquitous in aquatic ecosystems, and aquaculture production is susceptible to contamination from external or endogenous sources. This study investigated PL presence in water, fish feed and body sites of 55 European seabass produced in a recirculating aquaculture system (RAS). Fish morphometric parameters and health status biomarkers were determined. A total of 372 PLs were recovered from water (37.2 PL/L), 118 PLs from feed (3.9 PL/g), and 422 from seabass (0.7 PL/g fish; all body sites analysed). All 55 specimens had PLs in at least two of the four body sites analysed. Concentrations were higher in the gastrointestinal tract (GIT; 1.0 PL/g) and gills (0.8 PL/g) than in the liver (0.8 PL/g) and muscle (0.4 PL/g). PL concentration in GIT was significantly higher than in muscle. Black, blue, and transparent fibres made of man-made cellulose/rayon and polyethylene terephthalate were the most common PLs in water and seabass, while black fragments of phenoxy resin were the most common in feed. The levels of polymers linked to RAS components (polyethylene, polypropylene, and polyvinyl chloride) were low, suggesting a limited contribution to the overall PL levels found in water and/or fish. The mean PL size recovered from GIT (930 μm) and gills (1047 μm) was significantly larger than those found in the liver (647 μm) and dorsal muscle (425 μm). Considering all body sites, PLs bioconcentrated in seabass (BCFFish >1), but their bioaccumulation did not occur (BAFFish <1). No significant differences were observed in oxidative stress biomarkers between fish with low (<7) and high (≥7) PL numbers. These findings suggest that fish produced in RAS are mainly exposed to MPs through water and feed. Further monitoring under commercial conditions and risk assessment are warranted to identify potential threats to fish and human health and define mitigating measures.

Comparative Study of Flesh Quality, Blood Profile, Antioxidant Status, and Intestinal Microbiota of European Catfish (Silurus glanis) Cultivated in a Recirculating Aquaculture System (RAS) and Earthen Pond System.

With the increasing demand for European catfish, traditional extensive growth methods in polyculture are no longer sufficient to meet market needs. Therefore, this study aimed to identify indicators for improving recirculating aquaculture system (RAS) technology by determining and comparing growth performance, flesh quality, blood profile, oxidative status, and intestinal microbiota parameters between fish cultivated in a RAS and an earthen pond. Results revealed that RAS-grown fish had a higher fat content compared to pond-grown fish, while no significant differences were found for growth parameters. Sensory analysis showed no significant difference in taste between the two groups. Blood composition analysis showed small differences. Oxidative status analyses showed higher catalase and glutathione peroxidase activities in RAS-grown fish and slightly higher superoxide dismutase activity in pond-grown fish. Microbial analysis showed differences in the intestinal microflora, with a higher total number of aerobic germs and anaerobic germs and a lower total number of sulfite-reducing clostridia in RAS-grown fish. This study provides valuable insights into the comparative performance of a RAS and a pond rearing system in European catfish production, potentially informing future growth technologies.

Culture of dorado Seriola lalandi in Recirculating Aquaculture Systems low cost in the North of Chile

Culture of dorado Seriola lalandi in Recirculating Aquaculture Systems low cost in the North of Chile

Salinity as a tool for strain selection in recirculating land-based production of Ulva spp. from germlings to adults

The genus Ulva is globally distributed and has been thoroughly studied because of its functional biochemical composition, rapid growth rates and opportunistic features, and interest in Ulva cultivation is growing worldwide. In Europe, mostly near- and on-shore flow-through cultivation systems are used and land-based recirculating aquaculture systems (RAS) using fresh water or artificial seawater have not been developed for Ulva. While RAS provides quality control and can be located inland, maintenance costs are high. Using selected strains adapted to low-salinity could reduce seawater production costs and improve the economic feasibility. Therefore, our study assessed how salinity can be used as a tool for strain selection and optimization of functional traits. Growth rates and antioxidant activity of three species (four strains) of tubular and foliose Ulva from the NE-Atlantic and Mediterranean (foliose: Ulva lacinulata – two geographical strains, tubular: Ulva linza and Ulva flexuosa) were followed for three weeks at salinities ranging from 10 to 30 PSU. The tubular strains achieved optimal growth at a lower salinity than U. lacinulata. However, growth rates of both foliose strains were higher than of tubular strains, even at sub-optimal salinity. Therefore, U. lacinulata is a good candidate for RAS with artificial seawater, and the cost of salt can be reduced by up to 33.3% (20 PSU) without significantly reducing the growth rate of U. lacinulata. Higher antioxidant activity was achieved by reducing the salinity to 10 PSU for 10 days, suggesting that the functional traits of cultivated Ulva lacinulata can be optimized prior to harvest.

Morphologic and genic effects of waste pollution on the reproductive physiology of Paracentrotus lividus lmk: a mesocosm experiment.

A considerable amount of coastal contamination is caused by wastes deriving from household and the degradation and the metabolism of plants and animals, even if our attention is commonly focused on industrial pollutants and contaminants. Waste pollutants are mainly represented by highly diluted soluble compounds and particles deriving from dead organisms. This complex combination, consisting of suspended particles and dissolved nutrients, has a significant impact on coastal planktonic and benthic organisms, also playing an active role in the global cycles of carbon. In addition, production practices are nowadays shifting towards recirculated aquaculture systems (RAS) and the genic responses of target organisms to the pollution deriving from animal metabolism are still scarcely addressed by scientific investigations. The reservoir of organic matter dissolved in the seawater is by far the least understood if compared to that on land, cause only a few compounds have been identified and their impacts on animals and plants are poorly understood. The tendency of these compounds to concentrate at interfaces facilitates the absorption of dissolved organic compound (DOC) onto suspended particles. Some DOC components are chemically combined with dissolved metals and form complexes, affecting the chemical properties of the seawater and the life of the coastal biota. In this research, we compared the reproductive performances of the common sea urchin Paracentrotus lividus cultured in open-cycle tanks to those cultured in a recirculating aquaculture system (RAS), where pollution progressively increased during the experiment due to animal escretions. Sea urchins were cultured for 7months under these two conditions and their gametes were collected. Embryos resulting by in vitro fertilization were analyzed by Real Time qPCR to identify possible effects of pollution-induced stress. The fertility of sea urchins was evaluated, as well as the gonadosomatic indices and the histological features of gonads. Our results indicate that pollution due to excess of nutrients, event at sub-lethal concentrations, may hardly impact the reproductive potential of this key species and that chronic effects of stress are revealed by the analyses of survival rates and gene expression.

Sedimentation efficiency evaluation of an aquaculture tank through experimental floc characterization and CFD simulation

One of the most important parameters for the proper functioning of an aquaculture tank is water quality. The survival and healthy growth of fish depends on it. The main factors affecting water quality are the remains of food and feces of fish which form cohesive particles called flocs that are kept within the tank or in the modules of the recirculating aquaculture system (RAS). Through the application of non-invasive optical techniques such as particle tracking velocimetry (PTV) it was possible to experimentally characterize the particles from aquaculture tanks obtaining diameters and settling velocity distribution, which allowed estimating the effective density of the flocs. With these parameters, the discrete phase model (DPM) was applied using computational fluid dynamics (CFD) to estimate the position and velocity of the particles within a prototype tank with geometry that promotes hydrodynamics suitable for particles sedimentation while maintaining the conditions for fish growth. Through an experimental validation it was verified that by having a tank with circular geometry, central settler made of concentric cylinders, perimeter gratings and outlet spillway cone, it is possible to achieve an efficiency of 77.91–90% of particles sedimentation not exceeding 1 h in the process. Thus, through computer simulation coupled with experimental validation, it was possible to establish geometric parameters for the design of aquaculture tanks with self-cleaning characteristics under the sustainable scheme of water recirculation and reuse.

Dietary protein requirements of whiteleg shrimp (Penaeus vannamei) post-larvae during nursery phase in clear-water recirculating aquaculture systems

Whiteleg shrimp Penaeus vannamei farming in clear water recirculating aquaculture systems (RAS) is relatively recent, and consequently, knowledge on the shrimp dietary demands is still insufficient, particularly in the initial developmental stages. This study aimed at assessing the dietary protein requirement of whiteleg shrimp post-larvae (PL) in a clear-water recirculating aquaculture system (RAS). Six microdiets were formulated to contain 34%, 44%, 49%, 54%, 58%, and 63% crude protein (P34, P44, P49, P54, P58 and P63, respectively) and were evaluated in triplicates. Whiteleg shrimp PL (3.2 mg wet weight) were reared for 21 days in a clear-water RAS at Riasearch Lda. At the end of the feeding period, the optimal protein requirement was estimated at 47.1%, 46.4%, 47.2%, and 44.0% for weight gain, relative growth rate (RGR), feed conversion ratio (FCR), and survival, respectively. PL fed the P54, P58, and P63 diets achieved significantly higher final body weights than those fed P34. PL fed P34 showed significantly lower RGR and survival and significantly higher FCR values than those fed the remaining diets, suggesting that low protein diets may not be adequate to be used in this stage of shrimp development and/or for the clear-water RAS husbandry conditions. Moreover, diet P34 seemingly reduced the overall antioxidant status of the PL when compared to P44, P49, and P54. However, the P34 diet seems to have stimulated the PL immune mechanisms when compared to P44, P49, and P54, possibly due to increased levels of fish and algae oil. Similarly, despite the good growth performances, a diet containing 63% of protein also seemed to have compromised the overall shrimp PL antioxidant status and stimulate their immune system. Shrimp fed diet P54 showed an apparent overall superior antioxidant status when compared to the remaining diets, evidencing that using protein inclusion levels up to 54% in aquafeeds not only potentiates growth performances and survival but also can potentially be beneficial to the health status of P. vannamei PL grown in a clear-water RAS. Hence, results from this study suggest that a minimum of approximately 47% of protein should be considered when tailoring microdiets for whiteleg shrimp PL grown in a clear-water RAS, but inclusion levels up to 54% can be used with benefits to the PL antioxidant status.

Microbial community structure and diversity in fish-flower (mint) symbiosis

The fish-flower symbiosis model is an eco-friendly sustainable farming technology combining plants, fish and microorganisms in a recirculating aquaculture system. However, there are few studies on the structure and diversity of microbial communities in fish intestines, culture water and plant roots during fish-flower symbiosis. Here, we cultured carp (Cyprinus carpio), crucian carp (Carassius auratus) and grass carp (Ctenopharyngodon idella) with mint (Mentha spicala L.) and extracted total genomic DNA from intestinal microorganisms, culture-water microorganisms and root microorganisms for each fish species for high-throughput sequencing of 16S rRNA genes. Analysis of microbial community structure and diversity revealed changes in abundance of microbial genera in the intestines and culture water of each fish species, including changes in the dominant taxa. Pirellula, Truepera, Aquincola, Cetobacterium and Luteolibacter were widespread in the fish intestine, culture water and mint root system. This study revealed the effects of mint feeding on the structure and diversity of microbial communities of fish, water bodies and the mint root system during fish-flower symbiosis, providing a theoretical reference for the promotion and application of fish-flower (mint) symbiosis technology and healthy fish culture technology.

MortCam: An Artificial Intelligence-aided fish mortality detection and alert system for recirculating aquaculture

Mortality is an important production and fish welfare indicator in aquaculture. Unusual mortality patterns can be associated with abiotic or/and biotic stresses on fish in recirculating aquaculture systems (RAS). Real or near real-time mortality tracking can provide valuable inputs to farm managers, to make informed RAS management decisions and address root causes in an effort to prevent mass mortality events. While traditional systems use infrequent human operator observation and tracking - often in conjunction with an underwater camera - the proposed tool (i.e., ‘MortCam’) augments this approach with Artificial Intelligence (AI) and Internet of Things (IoT) deployed at the Edge to provide round-the-clock mortality monitoring and trigger alerts when mortality thresholds are exceeded. MortCam consists of an imaging sensor integrated with an edge computing device, customized for underwater applications. MortCam was deployed in a 150 m3 circular dual-drain RAS tank at 0.6 m above the bottom drain plate to acquire the imagery data in both ambient and supplemental light conditions. The images were collected every fifteen minutes for 90 days. Acquired images were annotated either as ‘alive’ or ‘dead’ fish and split into training (70 %), validation (20 %), and test (10 %) datasets to train a custom YOLOv7 mortality detection model. The optimized mixed model achieved a mean average precision (mAP) and F1 score of 93.4 % and 0.89, respectively. Additionally, the model performed well in terms of mortality count and was found robust despite changes in the imaging conditions. The model was deployed on the MortCam to achieve round-the-clock autonomous mortality monitoring. The system reliably generated email and text alerts to notify fish production staff of unusual mortality events.

Transient Numerical Study to Determine the Effect of Inlet Angle Variation on Flow Conditions inside a Circular Aquaculture Tank

Seeing how great the contribution and potential of the aquaculture sector to the fulfillment of food for the people of Indonesia, the development of aquaculture including the Recirculating Aquaculture System (RAS) is very important to be carried out intensively. An important aspect that should be considered for the development of RAS is maintaining water quality as the main medium of cultivation. Optimization of the aquaculture tank is an effort that can be conducted to achieve this goal. A transient numerical study to determine the effect of inlet angle variation on flow conditions inside a circular aquaculture tank was conducted to assess the optimum geometry for the application. Single-phase CFD simulations using the k-ω SST turbulent model were carried out to evaluate the effect of inlet nozzle angle variations. Three angle variations 0°, 45°, and 90° were selected and the resultant fluid flow conditions were analyzed. From the CFD results, it can be known that the optimum condition for the circular aquaculture tank is achieved for the angle 0° among the tested angle in this present study.

Lab- and pilot-scale photo-biofilter performance with algal–bacterial beads in a recirculation aquaculture system for rearing rainbow trout

AbstractIndustrial aquaculture has proliferated due to increased world demand for fish and seafood. Aerobic bacterial biofilters typically perform the nitrogen abatement of wastewater. Recirculation aquaculture systems (RAS) require nitrifying microorganisms developed in the biofilter. Despite the advantages of these biofilters, there are disadvantages, such as the time needed to mature, decrease in oxygen concentration, accumulation of organic matter and difficulty of backflushing, among others. On the other hand, microalgae effectively eliminate nutrients-pollutants, consuming inorganic carbon, nitrogen, and phosphorus and balancing soluble oxygen, conditions not attributable to nitrifying biofilters. The current study used a photo-biofilter to determine the depuration capacity of an immobilized co-culture of microalga Tetradesmus dimorphus and nitrifying bacteria isolated from a Salmon RAS. Bacteria frorm genera Flavobacterium, Microbacterium, Raoultella, Sphingobacterium, and Pseudomonas were identified. Biofilters were tested in sequential batch (lab-scale; 2.85 L) and continuous mode (pilot-plant scale; 120 L) attached to a RAS system for rearing rainbow trout. The algal–bacterial community structure was studied using 16S rRNA gene sequencing. Results showed that at typical loading rates, the algal–bacterial community could simultaneously remove ammonium, total ammonium nitrogen (TAN), nitrate and phosphate. Moreover, the system evaluated removed TAN daily, at an average of 1.18 kg per m3 of beads. Graphical Abstract

Effects of biological flocculation technology (BFT) on water quality dynamics and immune response of grass carp (Ctenopharyngodon idella)

The biofloc technology (BFT) offers benefits in improving feed utilization and reducing the feed conversion ratio compared to the recirculating aquaculture system (RAS). In this study, high-throughput 16S rRNA gene sequencing was employed to investigate and compare the bacterial communities in these aquaculture systems and the gut microbiota of grass carp reared in them. We observed a significant distinction between the microbial communities of the aquaculture systems and the intestinal microbiota of grass carp. The genera cetobacterium and bacillus were more abundant in the BFT system, accounting for only 0.05% and 0.25% in the RAS. Our study also demonstrated that BFT could influence the intestinal microorganisms of grass carp (Ctenopharyngodon Idella) by reducing the relative abundance of burkholderia-caballeronia-paraburkholderia and increasing that of cetobacterium. Based on bugBase community predictions, the potential pathogenicity in BFT and grass carp intestine was lower than in RAS. Regarding gene expression in the grass carp intestine, immunosuppressive genes showed higher expression, while pro-inflammatory genes exhibited lower expression in grass carp reared in BFT. Furthermore, the final average length and weight of grass carp in the BFT system were significantly higher than those in the RAS. This study provides valuable insights into gut microbiome ecology in relation to two grass carp aquaculture systems, which could be effectively applied in grass carp management to promote health and improve water quality.

Corticosteroid plasma kinetics and gonadal receptor gene expression during the reproductive cycle in female Eurasian Perch: Investigation of the roles of corticosteroids in vitellogenesis.

To improve the quality of reproduction in Eurasian perch, Perca fluviatilis L., which is a promising candidate for Eurasian freshwater aquaculture that is currently cultivated in recirculating aquaculture systems (RAS), investigating the hormones that mediate and affect reproduction in this species is indispensable. The literature defines a group of four major corticosteroids (11-deoxycorticosterone, 11-deoxycortisol, corticosterone and cortisol) that might mediate critical stages of reproduction in female perch. Unfortunately, neither the basic roles nor the kinetics of these four corticosteroids throughout the reproductive cycle of female perch have been well defined to date. In this study, we therefore elucidated the plasma kinetics of these four corticosteroids during the reproductive cycle of domesticated female perch while monitoring the expression of the different receptors and enzymes that mediate their production and possible functions. Additionally, we performed an invitro experiment during late vitellogenesis to investigate the possible direct roles of these steroids during that stage. Our results revealed that these four corticosteroids were detectable throughout the reproductive cycle, and the levels of most of them (11-deoxycorticosterone, 11-deoxycortisol, and cortisol) fluctuated significantly depending on the stage of reproduction. 11-Deoxycorticosterone and 11-deoxycortisol exhibited their highest levels, 1.8ng/ml and 58ng/ml, respectively, at the beginning of the reproductive cycle. By the end of the reproductive cycle, 11-deoxycortisol and cortisol plasma levels exhibited a surge, reaching 58ng/ml and 150ng/ml, respectively. During the perch reproductive cycle, the corticosteroid receptor complex is not regulated only at the hormone level, as the expression levels of all corticosteroid receptor genes showed a progressive and similar decline. In vitro exposure of vitellogenic oocytes to some of these corticosteroids (11-deoxycorticosterone and 11-deoxycortisol) induced an increase in yolk globule diameter and a decrease in the density of yolk globules, which indicates the involvement of both of these hormones in yolk globule coalescence. Taken together, these results implicate corticosteroids in the reproductive cycle, although the related cellular mechanisms remain to be investigated.

The dissolution of total suspended solids and treatment strategy of tailwater in a Litopenaeus vannamei recirculating aquaculture system

The dissolution of total suspended solids and treatment strategy of tailwater in a Litopenaeus vannamei recirculating aquaculture system