Sea Bass Fingerlings Research Articles

Early rearing of European seabass (Dicentrarchus labrax) with mild current enrichment modifies fish swimming behavior without altering their growth performance

The implementation of conditions that favor optimum swimming activity (e.g., suitable flow regimes), has been associated with enhanced growth and improved welfare in some farmed fish species. Despite the importance of European seabass in aquaculture, the potential beneficial effects of rearing flow conditions have not been sufficiently explored in this species. This study investigates how the application of fast (F, 0.01–0.20 m s-1) or slow (S, <0.01 m s-1) steady flows in rearing tanks for 75-77 days affected physiological and behavioral traits in seabass fingerlings. Growth performance, external and internal morphology, and several physiological variables, including hematocrit, plasma cortisol concentration, and osmotic and ionic balance were not affected by flow conditions during rearing. Also, behavioral tests implemented in groups or isolated individuals suggest that coping styles were not affected by the two tank-rearing conditions. On the contrary, the swimming behavior assessed in tests was modified by the flow condition experienced during rearing. Mean swimming speed, peak acceleration, swimming distance, angular velocity, and meander showed some variability across different tests and time, although consistently displaying higher values in seabass reared in the F condition, suggesting increased activity and more consistent swimming patterns in that group. However, the cumulative time in proximity between individuals measured in behavioral group tests suggested that group cohesion was variable, without displaying differences between F and S groups. These findings have particularly important implications for fish welfare and may suggest plasticity in the behavioral response to rearing conditions for this species, although not affecting the assignment of the individuals to the different coping styles. Summary statementWe investigated how mild current enrichment applied during early rearing in seabass modifies physiological and behavioral responses involving swimming activity, exploring the potential associations to fish welfare.

Exploring the detrimental effects of microplastics on Asian seabass (Lates calcarifer) fingerlings survival and health

Microplastics (MPs) are widely used and disposed of indiscriminately, posing a potential threat to aquatic life. Herein, Asian seabass (Lates calcarifer) fingerlings were exposed to various concentrations (1, 10 and 100 ppt or g/kg) of dietary polyethylene MPs for 16 days. The results indicated a significant increase in mortality among the fish fed with dietary MPs compared to the control. Furthermore, histological analysis of the liver revealed moderate-to-severe morphological alterations, hepatocyte necrosis and vacuolisation as the concentration gradient of MPs increased. The severity of the alterations was highest at a concentration of 100 ppt, indicating a direct correlation between MP and liver damage. In addition, RNA sequencing and Gene Ontology term enrichment analysis revealed that a total of 4137 genes were significantly differentially expressed, with 1958 upregulated and 2179 downregulated genes. The significantly enriched terms included ‘oxidoreductase activity’, ‘endocytosis’, ‘mitochondrial’, ‘immune system process’ and ‘lipid catabolic process’. Moreover, the Kyoto Encyclopaedia of Genes and Genomes enrichment analysis demonstrated that dietary MPs triggered oxidative stress, immune response and adaptive mechanism pathways in fish. Thus, MPs can induce metabolic disorders in L. calcarifer, highlighting their potential threat to aquatic organisms.

Optimizing the Supplementation of Calcium and Phosphorus in the Diets of Asian Seabass (Lates calcarifer) in Freshwater based Recirculating Aquaculture System

Background: Calcium and phosphorus are important mineral nutrients for all energy-producing cellular and metabolic pathways. Fish obtain Ca and P from their feed because of the low level of calcium and phosphorus in the freshwater especially in the RAS system. This study was investigated to evaluate the growth characteristics, survival rate, calcium and phosphorus composition and haematological and biochemical parameters of Asian Seabass (Lates calcarifer) under the influence of varied combinations of calcium and phosphorus in the formulated sinking feed. Methods: The experiment was carried out with Asian Seabass fingerlings, each with an initial average weight of 2.00±0.15 g which were randomly distributed in 54 Nos. of PE tanks with a volume of 500 Litres @ 30 Nos./tank. The experiment duration was 60 days and was carried out in a 6×3 factorial design. The fishes were fed with a sinking pellet diet containing calcium Ca 0.0, Ca 0.5% and Ca 1.0% and phosphorus P 0.0, P 0.5%, P 1.0%, P 1.5%, P 2.0% and P 2.5% and all the possible combinations of above percentages of calcium and phosphorus in the experimental diets. Result: The growth characteristics and survival rates were significantly higher in 1% of calcium and phosphorus-contained feed, the calcium and phosphorus composition and haematological and biochemical parameters also confirmed the experimental results. Our study outcome was useful for formulating a calcium and phosphorus-incorporated sinking feed to Asian Seabass for better growth in the recirculating aquaculture system.

Dietary Curcumin Nanoparticles Improve Growth Performance, Oxidative Status and Immune Response of European Seabass (Dicentrarchus Labrax)

Abstract A 90 days of feeding trial was employed for evaluating the effects of dietary supplementation with curcumin nanoparticles (CURNPs) on growth performance, hematological and biochemical parameters, immune response, antioxidant status, and intestinal and hepatic architecture in European seabass (Dicentrarchus labrax) fingerlings. Fish (n = 300, initial body weight = 10.02 g ± 0.11 g) received supplementary CURNPs at rates of 0 (control; CURNPs0), 50 (CURNPs50), 100 (CURNPs100) and 150 (CURNPs150) mg/kg diet for 90 days. Growth performance (final body weight (FBW), daily weight gain (DWG), weight gain (WG), relative growth rate (RGR), and protein efficiency ratio (PER)) and feed uptake (feed conversion rate (FCR)) were improved significantly in CURNPs (100 and 150 mg/ kg)-supplemented groups. The hematological parameters red blood corpuscles (RBCs), hemoglobin (Hb), and packed cell volume (PCV) were improved significantly (P&lt;0.001) in CURNPs150 and CURNPs100 groups, while CURNPs150 had the lowest values of monocytes (P = 0.019) and heterophils (P&lt;0.005) when compared with other groups. Glucose was higher and lipid profile (total cholesterol and triglycerides) were lower in all CURNPs-supplemented groups as compared to the control group. Fish fed with CURNPS at various levels exhibited remarkable increase in digestive enzymes (amylase and lipase), immune markers (immunoglobulin G (IgG), lysozyme and phagocytic indices), and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx)). A noticeable decrease (P&lt;0.05) in malondialdehyde (MDA) and considerable upregulation of hepatic insulin-like growth factor 1 (IGF1) and interleukin-1beta (IL-1β) mRNA levels were found in CURNPs-supplemented fish in a dose-dependent manner. The down regulation of hepatic heat shock protein 70 (HSP70) was observed in CURNPs150. Intestinal and hepatic architectures were improved significantly by CURNPs. In conclusion, CURNPs supplementation improved growth performance, feed consumption and digestion, hematological and biochemical markers, immune response, and redox homeostasis in D. labrax. Therefore, CURNPs could be supplemented in the diets of D. labrax as a natural alternative to promote overall performance.

The effects of nano-curcumin on growth performance, feed utilization, blood biochemistry, disease resistance, and gene expression in European seabass (Dicentrarchus labrax) fingerlings

Phytochemicals are used in fish farming to reduce stress and combat diseases during intensification. Recently, nanotechnology has represented a paradigm shift in the aquatic feed industry to improve the solubility, availability, and efficacy of phytochemicals. The purpose of this research was to investigate the effects of dietary supplementation with nano-curcumin (CUNE) on the growth, feed utilization, body composition, blood biochemistry, antioxidant status, disease resistance to Vibrio parahaemolyticus (V. parahaemolyticus), and the expression of insulin-like growth factor 1 (IGF-1), growth hormone (GH), interleukin-10 (IL-10), and interlukin-1β (IL-1β) genes in European Seabass (Dicentrarchus labrax) fingerlings. Fish (6.02±0.01) were randomly divided into four equal groups and fed varying levels of CUNE: 0 (CUNE0), 50 (CUNE1), 60 (CUNE2), and 70 mg/kg (CUNE3) of nano-curcumin for 56 days, respectively. The inclusion of dietary CUNE significantly improved the growth indices (final body weight and weight gain, and specific growth rate) and feed utilization (improved feed intake and lower FCR) of European seabass fingerlings (p<0.05). However, CUNE inclusion had no significant effect on body composition including the percentages of dry mater, crude protein, crude lipid, and ash (p>0.05). All CUNE groups established an enhancement in blood hematology in a dose-dependent manner, with CUNE3 demonstrating the highest values. CUNE supplementation (70 mg/kg diet) produced the highest levels of total protein, albumin, globulin, and triglycerides, as well as the lowest levels of glucose, and hepatic enzymes (ALT, AST, and ALP; p<0.05) compared to other groups. Furthermore, the CUNE-supplemented groups showed significant improvements in superoxide dismutase, catalase, and glutathione peroxidase, while reducing malondialdehyde (p<0.05). Additionally, the consumption of CUNE increased the expression of IGF-1, GH, and IL-10 genes in a dose-dependent manner (p<0.05). Interestingly, fish fed 70 mg of CUNE in their diets had lower expression of the IL-1β gene compared to the other groups (p<0.05). When the fish were challenged with V. parahaemolyticus, the addition of CUNE in their diets resulted in reduced mortality rates. Therefore, nano-curcumin could be considered as a natural feed additive to promote growth, feed utilization, and bacteria resistance via supporting antioxidant status, serum metabolites, and the regulation of GH, IL-10, and IGF-1 in the hepatic tissues of European seabass fingerlings.

Improving the Aerobic Capacity in Fingerlings of European Sea Bass (Dicentrarchus labrax) through Moderate and Sustained Exercise: A Metabolic Approach.

Sustained swimming induces beneficial effects on growth and energy metabolism in some fish species. However, the absence of a standardized exercise regimen that guarantees an optimal response to physical activity is due to the anatomical, behavioral, and physiological differences among species, and the different conditions of tests applied, which are especially notable for the early stages of cultured species. The objective of this study was to assess the growth and metabolic responses of European sea bass submitted to continuous and moderate exercise exposure, selecting a practical swimming speed from swimming tests of groups of five fingerlings. The exercise-effects trial was carried out with 600 sea bass fingerlings (3-5 g body weight) distributed in two groups (control: voluntary swimming; exercised: under sustained swimming at 1.5 body lengths·s-1). After 6 weeks, growth parameters and proximal composition of both muscles were not altered by sustained swimming, but an increased synthetic capacity (increased RNA/DNA ratio) and more efficient use of proteins (decreased ΔN15) were observed in white muscle. The gene expression of mitochondrial proteins in white and red muscle was not affected by exercise, except for ucp3, which increased. The increase of UCP3 and Cox4 protein expression, as well as the higher COX/CS ratio of enzyme activity in white muscle, pointed out an enhanced oxidative capacity in this tissue during sustained swimming. In the protein expression of red muscle, only CS increased. All these metabolic adaptations to sustained exercise were also reflected in an enhanced maximum metabolic rate (MMR) with higher aerobic scope (AMS) of exercised fish in comparison to the non-trained fish, during a swimming test. These results demonstrated that moderate sustained swimming applied to sea bass fingerlings can improve the physical fitness of individuals through the enhancement of their aerobic capacities.

Characterization of a New Toti-like Virus in Sea Bass, Dicentrarchus labrax.

The European sea bass Dicentrarchus labrax is the main species reared in Mediterranean aquaculture. Its larval stage, which is very sensitive and highly affected by sanitary and environmental conditions, is particularly scrutinized in hatcheries. Recently, a Mediterranean sea bass farm had to deal with an abnormal increase in mortality, especially between 20 and 35 days post-hatching (dph). Biological investigations led to the observation of cytopathic effects on three different fish cell lines after almost 3 weeks of culture at 14 °C in contact with homogenized affected larvae, suggesting the presence of a viral agent. High-throughput sequencing revealed a 6818-nucleotide-long RNA genome with six putative ORFs, corresponding to the organization of viruses belonging to the Totiviridae family. This genome clustered with the newly described and suggested Pistolvirus genus, sharing 45.5% to 37.2% nucleotide identity with other piscine toti-like viruses such as Cyclopterus lumpus toti-like virus (CLuTLV) or piscine myocarditis virus (PMCV), respectively. Therefore, we propose to name this new viral agent sea bass toti-like virus (SBTLV). Specific real-time RT-PCR confirmed the presence of the viral genome in the affected larval homogenate from different production batches and the corresponding cell culture supernatant. Experimental infections performed on sea bass fingerlings did not induce mortality, although the virus could be detected in various organs and a specific immune response was developed. Additional studies are needed to understand the exact involvement of this virus in the mortality observed in hatcheries and the potential associated cofactors.

Growth performance, feed utilization, and resistance to acute crowding of post‐metamorphic stage black sea bass Centropristis striata reared at high stocking densities in a pilot recirculating nursery

AbstractA reliable and cost‐effective source of fingerlings is essential for the successful commercial aquaculture of black sea bass. This study aimed to determine the effects of nursery tank stocking densities on the growth performance, feed efficiency, survival, tolerance to shipping, and biochemical quality of juvenile black sea bass. In two experiments, different stocking densities were compared for black sea bass at different stages of development. In Experiment 1, intermediate stage juveniles (1.27 g mean wt) were stocked at densities of 4.5 and 6.5 fish per liter of tank volume. Growth performance and biochemical quality were similar between the two density treatments. In Experiment 2, early post‐metamorphic stage juveniles (mean wt. = 0.524 g) were compared using the same stocking densities. While the fish reared at 4.5 fish/L were slightly larger, there were no significant differences in growth performance or biochemical quality between the density treatments. After both experiments, the fingerlings from each density treatment showed high survival rates under acute crowding and simulated shipping conditions. The study demonstrates that high NT densities of 4.5 and 6.5 fish/L did not negatively impact the growth performance and quality of black sea bass fingerlings, providing transport‐ready fingerlings in a relatively short period.

Utilization of calcium-rich groundwater desalination concentrate in aquaculture

Global production of desalinated water increased greatly over the past three decades. Brackish water desalination is energetically favorable compared with seawater desalination, but high treatment costs and negative environmental impact of the concentrate byproduct hinders its development in semi-arid regions. The present study assessed key considerations associated with potential commercial aquaculture in high-flowrate calcium-rich groundwater desalination concentrate. European seabass (Dicentrarchus labrax) fingerlings, weighing 20–40 g were cultivated in brackish water (control), raw concentrate, and partially softened concentrate under flow-through conditions. Aside from two disease-related mortality events, fish survival exceeded 92% during 70 days of cultivation in all water types. The highest average growth rate of 0.26 g d−1 was obtained in the partially softened concentrate, which was 27% and 83% higher than in the raw concentrate and in the control, respectively. Substantial mineral precipitation on equipment and minor gill damage were observed in fish tanks receiving raw concentrate, projecting serious operational issues under commercial application. Preliminary aeration-softening of the concentrate relieved CO2 supersaturation and prevented precipitation issues. Several implementation options in a case study fish farm predict commercial and environmental feasibility in specific locations.

Distinctive location of piscine intestinal coccidiosis in Asian seabass fingerlings.

Coccidian infection (coccidiosis) is one of the most important causes of illness and death in the fish population, including Asian sea bass. The fingerling developmental stage is sensitive to various infectious agents. Economic losses are sustained by the sea bass aquaculture industry due to coccidiosis annually. However, the related pathological changes in the Asian sea bass fingerlings' three-part intestine remain unknown. This study aimed to investigate the Asian sea bass fingerlings' infection rate, infection location and site, and specific pathological lesions in the small intestinal tissues in a marine cage farming operation. A cross-sectional study was conducted on 44 fingerling fishes. Major coccidia proportions were identified morphologically at both the macroscopic and microscopic levels. The infection number was determined based on coccidia presence at various intestinal locations and sites. All areas were assessed for pathological lesions using semi-quantitative grading. Analysis of variance was used to perform all data analyses using the SPSS software. Data were expressed as means ± standard deviation. p < 0.05 was considered statistically significant. All Asian sea bass fingerlings studied were infected with coccidia. Enteritis and mucosal necrosis were distinct lesions found in the anterior intestine, which had the highest infection rate (49.94%), followed by the mid intestine (35.63%), and the posterior intestine (22.43%). The most common coccidian infection site was extracellular (subepithelial), followed by intracytoplasmic, and epicellular sites. Histopathological lesion determination revealed that intestinal tissue inflammation and epithelial injuries were predominantly seen in the anterior gut (p < 0.05). There was a high coccidian infection rate in Asian sea bass fingerlings from marine cage farming operations. Infection and intestinal damage at the anterior intestine, a major site, led to fingerling death. Disease prevention in the nursery should be intensive from the fingerling period to decrease the fatality rate caused by coccidia.

Growth performance, blood biochemical parameters, immune response, and antioxidant defense of Asian seabass (Lates calcarifer) fingerlings exposed to monovalent and bivalent vaccines against Streptococcus iniae and Vibrio harveyi

Growth performance, blood biochemical parameters, immune response, and antioxidant defense of Asian seabass (Lates calcarifer) fingerlings exposed to monovalent and bivalent vaccines against Streptococcus iniae and Vibrio harveyi

Monitoring Infection and Antibiotic Treatment in the Skin Microbiota of Farmed European Seabass (Dicentrarchus Labrax) Fingerlings.

The microbiota of fish skin, the primary barrier against disease, is highly dynamic and modulated by several factors. In fish aquaculture, disease outbreaks occur mainly during early-life stages, with associated high economic losses. Antibiotic treatments sometimes remain the best option to control bacterial diseases, despite many reported negative impacts of its use on fish and associated microbiota. Notwithstanding, studies monitoring the effects of disease and antibiotic treatment on the microbiota of fingerlings are scarce. We sequenced the bacterial 16S rRNA V4 gene region using a metabarcoding approach to assess the impact of a mixed infection with Photobacterium damselae ssp. piscicida and Vibrio harveyi and subsequent antibiotic treatment with flumequine, on the skin microbiota of farmed seabass (Dicentrarchus labrax) fingerlings. Both infection and antibiotic treatment led to a significant increase in bacterial diversity and core microbial communities and impacted microbiome structure. Dysbiosis was confirmed by changes in the abundance of potential pathogenic and opportunistic bacterial taxa. Skin bacterial metabolic function was also significantly affected by flumequine administration, suggesting a detriment to fish skin health. Our results add to an increasing body of literature, showing how fish microbiome response to infection and antibiotics cannot be easily predicted.

Effects of Dietary Bovine Lactoferrin on Growth Performance and Immuno-physiological Responses of Asian Sea Bass (Lates calcarifer) Fingerlings.

The aim of this study was to evaluate the effects of lactoferrin (Lf) on growth and feeding performance, biochemical and immune parameters in Asian sea bass (Lates calcarifer). A basal diet was supplemented with 0 (control), 400 (400 Lf), or 800 (800 Lf) mg Lfkg-1 diet. The results indicate a significant increase in innate immune parameters when the diet was supplemented with 800 mg Lf kg-1. The highest serum albumin value and the lowest serum glucose concentration were observed in 800 Lf group. The liver catalase activity in the 400 Lf and 800 Lf groups was lower than the control value. Moreover, malondialdehyde concentration in the liver of Asian sea bass was increased with increasing the dietary Lf supplementation. The results of the study suggest that supplementing diet with 800 mg Lf kg-1 stimulates non-specific immune response in Asian sea bass. Nonetheless, selecting an appropriate dose can be difficult, especially since both the higher and the lower dose tested may result in adverse effects.

Characterization of red-spotted grouper nervous necrosis virus isolated from ovarian fluids of asymptomatic wild Asian seabass, Lates calcarifer

Viral nervous necrosis (VNN) caused by nervous necrosis virus is a serious disease affecting a wide range of marine, brackishwater and freshwater fishes. The disease causes acute mortalities in larval and early juvenile stages while adult fishes are asymptomatic and remain as carriers of the virus. In the present study, nervous necrosis virus was isolated from ovarian fluids of asymptomatic wild-collected Asian seabass, Lates calcarifer in SSN-1 cell line. The complete genome of the virus was amplified by PCR from plaque purified virus and sequenced. Bioinformatic analysis of the sequence revealed that the isolate belonged to red-spotted grouper nervous necrosis virus. The virus purified from infected SSN-1 cell culture supernatants by cesium chloride gradient ultracentrifugation resulted in two bands in the gradient. Both the bands on SDS-PAGE analysis and western blot revealed a single 40 kDa capsid protein. The virus replication was optimum at 26–28 °C in vitro and the virus can be completely inactivated using 3 mM binary ethylenimine in 32 h at 25 °C. The isolated virus was infectious and caused 100% mortality in Asian seabass larvae. The inactivated virus when injected to Asian seabass fingerlings produced neutralizing antibody titre ranging from 1:320 to 1: 1280. The isolate is a potential candidate for production of an inactivated vaccine against VNN.

Ceratothoa oestroides Infection in European Sea Bass: Revealing a Long Misunderstood Relationship.

Ceratothoa oestroides (Cymothoidea, Isopoda) is a generalist crustacean parasite that negatively affects the economic sustainability of European sea bass (Dicentrarchus labrax) aquaculture in the North-East Mediterranean. While mortalities are observed in fry and fingerlings, infection in juvenile and adult fish result in approximately 20% growth delay. A transcriptomic analysis (PCR array, RNA-Seq) was performed on organs (tongue, spleen, head kidney, and liver) from infected vs. Ceratothoa-free sea bass fingerlings. Activation of local and systemic immune responses was detected, particularly in the spleen, characterized by the upregulation of cytokines (also in the tongue), a general reshaping of the immunoglobulin (Ig) response and suppression of T-cell mediated responses. Interestingly, starvation and iron transport and metabolism genes were strongly downregulated, suggesting that the parasite feeding strategy is not likely hematophagous. The regulation of genes related to growth impairment and starvation supported the growth delay observed in infected animals. Most differentially expressed (DE) transcripts were exclusive of a specific organ; however, only in the tongue, the difference between infected and uninfected fish was significant. At the attachment/feeding site, the pathways involved in muscle contraction and intercellular junction were the most upregulated, whereas the pathways involved in fibrosis (extracellular matrix organization, collagen formation, and biosynthesis) were downregulated. These results suggest that parasite-inflicted damage is successfully mitigated by the host and characterized by regenerative processes that prevail over the reparative ones.

Effect of alternate feeding with fish oil‐ and peanut oil‐based diets on the growth and fatty acid compositions of European seabass fingerlings ( Dicentrarchus labrax ) in the recirculated systems

The aim of this study was to evaluate the effects of alternate feeding regime with fish oil- and peanut oil-based diets on fatty acid profiles and growth performances of European seabass fingerlings (Dicentrarchus labrax). Six trials were implemented; fish oil trial [C; continuously fed by diet with fish oil (FO)], peanut oil trial [P; continuously fed by diet with peanut oil (PO)], mixture oil trial (PC; continuously fed by diet containing both %50 FO and %50 PO), alternate cycled feeding three trials [(3P/3C; fish fed by diet with PO for 3 weeks and FO for the following 3 weeks), (3PC/3C; fish fed by diet with PC for 3 weeks and FO for following 3 weeks) and (9P/3C; fish fed by diet with P for 9 weeks and C for following 3 weeks)] for 12 weeks. Significantly higher SGR and the best FCR were detected in P and 3PC/3C and 9P/3C groups, respectively, compared with C group (p > 0.05). The lowest HSI and VSI were in the C group (p > 0.05). The highest crude protein was determined in 3P/3C group while protein ratios were higher in cycled fed groups than in the experimental groups (p > 0.05). The highest crude lipid were detected in P group (p > 0.05). The higher SFA level was detected in 9P/3C group (p < 0.05), whereas C group had the lowest content. While P group had the highest fillet MUFA content, which was predominantly made up of OA, the lowest MUFA was determined in the 3PC/3C and C groups. The highest LA was observed in C group (p < 0.05). The ArA was higher in the cycled fed groups than the diet groups. EPA, n-3 PUFA and n3/n6 rates were significantly higher (p < 0.05) in cycled fed groups, compared with the diet groups. The DHA ratio was significantly lower in 9P/3C group compared with the other groups. Also, the lipid quality of the flesh was directly related to the EPA and DHA ratios, and a higher quality product was revealed at the end of cycled feeding with the low IA, IT and high FLQ and h/H values obtained. This study shows that cycled feeding regimes by diets including vegetables oil and FO may be used in European seabass culture.

Brown seaweed Sargassum polycystum as dietary supplement exhibits prebiotic potentials in Asian sea bass Lates calcarifer fingerlings

Seaweeds are known to contain nutrients that are essential for human nutrition, making them edible and potential resources to mine for bioactive substances. The present study was aimed to investigate the prebiotic potentials of the seaweed, Sargassum polycystum as supplement in diets for Asia sea bass fingerlings. Experimental dietary formulations were supplemented with four graded levels of powdered seaweed (0.0, 1.5, 3.0 and 4.5 %) and fed to sea bass fingerlings (mean initial weight 2.2 g) for 55 days. Fish were evaluated for feed efficiency, growth performance and mortality. The results showed that survival, feed consumption and efficiency, and growth performance were better in fish fed the 1.5 and 3.0 % seaweed supplemented feed compared to the control. Carcass protein and Fe contents, red blood cell (RBC) and white blood cell (WBC) counts were also better in the fish fed the sargassum supplemented diets, which were significantly (p < 0.05) higher in the 1.5 and 3.0 % treatments than in the control. Proliferation of pure colonies of descendant Gram positive, none-spore forming, cocci and rod-shaped, catalase and oxidase negative bacteria was observed in the intestines of fish reared with the sargassum supplemented feed. These bacteria were identified as Lactobacillus paracasei subspecies paracasei, which were earlier identified to exhibit probiotic characteristics. Taken together, these results demonstrated the prebiotic potentials of sargassum, S. polycystum for Asian sea bass fingerling when supplemented in their diets at concentrations of between 15 and 30 g/kg. The commercial cultivation of sargassum seaweed needs to be encouraged.

An indel in the Suv39h1 gene is associated with resistance to iridovirus in the Asian seabass

Suv39h1 is a member of the Suv39h sub-family of histone lysine methyltransferases. The gene plays an important role in heterochromatin organization, chromosome segregation, and mitotic progression in humans and model organisms. However, its functions in food fish species remain largely unknown. We identified the full-length cDNA of the Suv39h1 in the Asian seabass, analysed its genomic structure and identified polymorphisms. The gene was expressed in all tissues examined, but highly expressed in the gill, spleen and kidney. After challenging Asian seabass juveniles with iridovirus, the expressions of the gene altered, suggesting that the gene is related to the infection by iridovirus. Three SNPs and one indel were detected in the 3’ UTR of the gene. The indel was significantly associated with the resistance against iridovirus. In silico-mapping revealed that the gene was mapped to chromosome 6, where a significant QTL for the resistance to iridovirus was located previously in the Asian seabass. Altogether, the data suggest that the gene Suv39h1 play an important role in iridovirus resistance in the Asian seabass. This study also laid the foundation for further detailed analysis of the function of the Suv39h1 gene in resistance to iridovirus. The indel may supply a useful DNA marker for selecting Asian seabass fingerlings resistant to iridovirus.

Biosafety, withdrawal and efficacy of anti-parasitic drug emamectin benzoate in Asian Seabass (Lates calcarifer)

Parasitic infestations are frequently reported in brackishwater fish. Hence, prevention and control strategy is paramount for successful brackishwater aquaculture. Emamectin benzoate (EMB) is found to be an effective in-feed treatment for controlling several ecto-parasites in fish. The objective of this study was to understand the biosafety, withdrawal and efficacy of EMB for use in brackishwater reared Asian Seabass (Lates calcarifer) under tropical climate. Biosafety was evaluated at doses of 0, 50, 250 and 500 μg kg−1 of fish body weight (BW) day−1 for 21 days. EMB was administered per os through coated pellet feed. Gross, haematological and histopathological observations were made and found that there were no biologically significant adverse changes between control and treated groups. Withdrawal period was estimated with similar experiment with same doses but for seven consecutive days. Samples were collected on 0th, 7th, 14th, 21st and 28th day of post-medication for QTRAP 4000 LC-MS/MS analysis. The data showed that the level of EMB in whole fish treated with 50, 250 and 500 μg kg−1 of fish BW day−1 were 21.0 ± 0.0, 142.4 ± 0.1 and 209.7 ± 0.1 parts per billion (ppb) on 0th day of withdrawal, respectively. These values were found drastically decreased on 7th day of withdrawal and reached undetectable level by 28th day. For assessing the environmental safety, acute immobilization test was conducted using 24 h old daphnid. The EC50 and LC50 values in daphnids were 107 and 160 times higher than the the treatment dose, respectively. Efficacy was tested with the therapeutic dose on Asian Seabass fingerlings infested with naturally sea louse (Caligus minimus). Medicated pellet feed was fed at 4% BW day−1 divided equally between three feedings. Efficacy trial showed that there was significant improvement in survival (92.0 ± 2.3%; P < .01), reduction in parasitic load (P < .05), percent efficacy (76.2%) and haematological parameters (P < .01; P < .05) on and after fifth day of treatment. Based on the results, it was concluded that there was an adequate margin of safety and 100% efficacy associated with administering EMB-medicated feed to Asian Seabass fingerlings at the proposed therapeutic treatment regimen of 50 μg of EMB kg−1 fish BW day−1 for seven consecutive days.

Streptococcosis in freshwater farmed seabass Lates calcarifer and its virulence in Nile tilapia Oreochromis niloticus

This study investigated disease outbreaks caused by Streptococcus iniae in freshwater pond-cultured seabass Lates calcarifer in Thailand. The affected fish exhibited typical signs of streptococcal infection except for the ophthalmological lesions. Four putative S. iniae isolates (CU/KSC1, CU/KSC2, CU/KSC3 and CU/KSC4) were identified based on phenotypic characteristics and PCR amplification of the 16S rRNA gene. Phylogenetic analysis of the partial (1234 bp) 16S rRNA nucleotide sequences revealed that CU/KSC1–3 clustered within the group of S. iniae previously reported from diseased Nile tilapia in Thailand, while CU/KSC4 was more distant. Infectivity trials in seabass fingerlings (approximately 7 g bodyweight) via intraperitoneal injection (IP) showed >60% accumulative mortality (63.3–83.3%) in the fish that received 106 colony forming units (CFU) fish−1 of either isolate at 10 d post infection (dpi). A similar IP challenge protocol using the most virulent isolate (CU/KSC4) was conducted to examine the pathogenicity of the seabass isolate in Nile tilapia Oreochromis niloticus. A lower mortality, compared to that of the laboratory infected seabass, was observed in Nile tilapia, where the mortality at 10 dpi was 26.7, 30 and 33.3% in Nile tilapia receiving S. iniae at 10 (Bromage and Owens, 2002), 106 and 107 CFU fish−1, respectively. Moreover, S. iniae was re-isolated from the kidney of both affected fish species, but not from the surviving fish. However, the intestines obtained from these survivors were PCR positive for S. iniae, giving the possibility that the bacteria may be excreted into the rearing water via feces. To our knowledge, this is the first report of S. iniae isolated from disease occurrences in freshwater-inland cultured seabass in Thailand.