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Feed is the main source of material and energy for farmed fish, and its nutritional value and balance are important factors affecting fish's growth rate and physical health. In order to explore the effects of two different feed sources on the growth, serum biochemical indexes, liver antioxidant capacity, and lipid metabolism of young cobia fish, 300 young cobia fish with an initial body weight of 43.14 ± 1.25 g were selected for the experiment and randomly divided into two treatments. Each treatment had five replicates, and each replicate had 30 fish. They were fed with formulated feed and frozen fresh fish, respectively, for 12 weeks. The results showed that the weight gain rate, specific growth rate, and feed conversion rate of juvenile cobia fish fed with formulated diet were extremely significantly lower than those of the frozen fresh fish group (P < 0.01), and condition factor was significantly lower than that of the frozen fresh fish group (P < 0.05). However, protein efficiency rate, hepatosomatic index, and viscerosomatic index were significantly higher than those of frozen fresh fish group (P < 0.05). The content of water, crude protein, and crude ash in the whole fish had no significant difference (P > 0.05), while the content of crude lipid decreased significantly (P < 0.05). The serum aspartate aminotransferase activity and sugar content of cobia in the formulated diet group were significantly higher than those in the frozen fresh fish group (P < 0.05). In contrast, the total cholesterol, triglyceride content, alkaline phosphatase activity, and phosphorus content were significantly lower than those in the frozen fresh fish group (P < 0.05). Compared with the frozen fresh fish group, the antioxidant enzyme activities in the liver of the formulated diet group were significantly decreased (P < 0.05) except malondialdehyde (MDA) and the activity of fatty acid synthase, while there was no significant difference in the malate dehydrogenase. The study showed that under the experimental conditions, frozen fresh fish was more suitable for feeding juvenile cobia, and the formulated diet had adverse effects on the liver of juvenile cobia. Therefore, the nutritional composition of frozen fresh fish and the metabolic characteristics of cobia were used for reference to optimize and adjust the nutritional formula of juvenile cobia. [ABSTRACT FROM AUTHOR]

The diseased cage-cultured cobia (Rachycentron canadum) displayed clinical signs, haemorrhagic eyes, dorsal darkness and gross pathological lesions, enlargement of spleen and liver. Haemorrhages were found in brain, heart and liver with cumulative mortality rates ranging from 20% to 50%. Extensive congestion in the heart, liver, spleen, kidney and brain was observed histopathologically. Epicarditis and meningitis were also revealed in diseased cobia. All isolates recovered from the organs (liver, spleen, head kidney, posterior kidney, brain and muscle) of cobia were found to be gram-positive, non-motile, ovoid cocci, short-chain-forming (diplococci) and a-haemolytic. The API 32 strep system together with the polymerase chain reaction assay for species-specific primers (pLG1 and pLG2) and the internal transcribed spacer (ITS) region (G1 and L1 primers) confirmed all four selected isolates as Lactococcus garvieae. Partial 16S rDNA nucleotide sequence (~1,100 bp) of one representative L. garvieae isolate AOD109191 (GenBank accession number, MW328528.1) shared 99.9% identities with the 16S rDNA nucleotide sequence of L. garvieae (GenBank accession numbers: MT604790.1). Transmission electron microscopy (TEM) evaluation of one representative L. garvieae isolate (AOD109191) and the results of multiplex PCR did not reveal the presence of the capsular gene cluster (CGC), thus categorizing the isolate as the KG+ phenotype. Capsule staining and TEM observations confirmed the presence of a hyaluronic acid-like capsule, a possible virulence factor in KG+ phenotype L. garvieae isolates. The pathogenic potential of the representative isolate (AOD109191) was assessed through intraperitoneal injection challenges in cobia. The gross lesions and histopathological changes found in experimentally infected cobia were similar to those seen in naturally infected fish. This is the first report that confirms L. garvieae-induced 'warm water lactococcsis' can cause outbreaks of diseases in cage-cultured cobia. [ABSTRACT FROM AUTHOR]

In this study, juvenile cobia fish (Rachycentroncanadum) (body weight: 50.44 ± 2.78 g) were used as a study object to investigate the effects of hypoxia stress (dissolved oxygen: 3.15 ± 0.21 mg/L) on the activities of their digestive enzymes, intestinal morphology and relative expression of tight junction proteins coding genes. Under the experimental conditions, the juvenile cobia were given 28 days of hypoxia stress. The results showed that the activities of digestive enzymes in the intestines of the hypoxia stress group decreased. In addition, the amylase and lipase activities decreased significantly (p < 0.05), and the trypsin activity in the hypoxia stress group compared to that in the control group. The morphology and structure of the intestine also showed significant changes. Under the microscopic observation, the mucosal fold height and muscle thickness of the intestine showed a significant decrease (p < 0.05); also, the villi's width showed a significant decrease (p < 0.05) in the hypoxia stress group as compared to that in the control group. The observation under a transmission electron microscope showed that the microvilli of juvenile cobia in the hypoxia stress group were irregularly arranged, atrophied and fallen off compared to the control group. Furthermore, there were gaps in the tight junction. In addition, the boundary between cells was unclear. The relative expression of intestinal tight junction proteins coding genes was down‐regulated to varying degrees. The mRNA expressions of ZO‐1 and claudin‐4 were significantly down‐regulated (p < 0.05) and ZO‐2 and occludin in the hypoxia stress group compared to those in the control group. These results indicated that hypoxia stress could inhibit the activities of intestinal digestive enzymes, damage intestinal morphology and decrease the expression of tight junction proteins coding genes in cobia. The present study provided a scientific foundation for evaluating the multifaceted impacts of hypoxia stress on fish species, such as cobia. [ABSTRACT FROM AUTHOR]

Environmental salinity is a major factor influencing growth and development, reproduction, and physiology in fish. Recently, miRNAs have been confirmed to play an important role in regulating organismal adaptation in salinity challenge. Since the genomic studies on cobia (Rachycentroncanadum) are limited, the miRNA transcriptome of R. canadum is important to investigate the salinity adaptation. In this study, the miRNA transcriptome analysis of the gills in R. canadum was performed under conditions of normal salinity (30‰) and low salinity (10‰). In total, 409 known miRNAs and 139 novel miRNAs were identified, with 56 DEMs (differentially expressed miRNAs). There were 64,983 target genes predicted based on the R. canadum transcriptome, in which 43,283 target genes were attributed to DEMs. The GO annotation and KEGG pathway analysis of target genes indicated that metabolic pathways and signal transduction were the most strongly affected pathways in R. canadum to tackle low‐salinity stress, and R. canadum maintains osmotic homoeostasis and energy balance by regulating miRNAs in metabolism, ion channels, and transporters to adapt to low salinity. Overall, this study provides valuable genomic resources to further understanding the fundamental mechanisms of miRNA regulation in marine teleost response to hypoosmotic stress adaption. [ABSTRACT FROM AUTHOR]

Methionine (Met) plays important roles in protein synthesis and in diverse cellular processes in eukaryotes. In the present study, primary muscle cells of cobia fish Rachycentron canadum were isolated and treated with Met at different concentrations (0.5, 1, 2, 5 or 10 mM) for 24 h in culture media. The results show that the 5 mM Met group had the highest cell viability and total protein content. The phosphorylation levels of phosphoinositide 3‐kinase (PI3K) p85 on Tyr458 and of protein kinase B (Akt) on Ser371 were significantly affected by the Met concentration during incubation. Cells incubated with 5 or 10 mM Met showed higher mRNA levels of the target rapamycin (TOR) and higher phosphorylation levels of TOR on Ser2448. Cells incubated with 5 mM Met had the highest phosphorylation levels of ribosomal p70‐S6 kinase (S6K1) on Ser371 and of 4E‐binding protein 1 (4E‐BP1) on Thr37/46. Cells incubated with PI3K and TOR inhibitors showed that LY294002 and rapamycin significantly inhibited the phosphorylation of Akt on Ser371 and of TOR on Ser2448 respectively. These results indicate that Met concentration affects cell viability and is associated with changes in the PI3K/Akt/TOR pathway. [ABSTRACT FROM AUTHOR]

Cobia Rachycentron canadum is an economically important fish and is cultured throughout southern China and other part of the world. However, the knowledge of metabolism and nutritional requirements of cobia embryos remains limited. This study investigated changes of the biochemical composition, as well as the activities of related digestive and antioxidant enzymes during the development of both eggs and yolk‐sac larvae of the cobia (Rachycentron canadum). The results showed that egg mass at the fertilized stage increased gradually to the blastula stage and showed a significant increase at the segmentation stage and a significant decrease at the larval period. The main components of embryos and larvae were carbohydrates, lipids and proteins. Protein and lipid contents decreased at the blastula stage, increased significantly at the segmentation stage and then decreased thereafter. Carbohydrate contents decreased significantly during the development. Enzymatic activities showed a progressive increase from the embryo to the yolk‐sac larval stage. The activities of pepsin and trypsin increased significantly during the development. Amylase activity remained low before the blastula stage and increased rapidly thereafter. Lipase showed an 'increase–stable–increase' tendency. Changes of digestive enzyme activities indicated the dynamics of the biochemical composition. Activities of glutathione peroxidase, catalase and superoxide dismutase significantly increased during embryonic and yolk‐sac stages, and malondialdehyde contents followed the same trend. The results of the current research provide vital information to enhance yolk exploitation with a specific focus on organogenesis. Moreover, considerable knowledge on the embryonic development of the cobia is presented. [ABSTRACT FROM AUTHOR]

In the case of coinfections, multiple pathogens induce pathologies independently or in combination. The present study describes the pathological and microbiological characterization of Vibrio harveyi and two strains of Photobacterium damselae subsp. damselae causing coinfection in cobia reared in sea cages. All the isolated pathogens were virulent to juvenile cobia by injection challenge. The experimental challenge with the three isolated pathogens singly or in combination revealed a significant difference in the mortality profile. Lesions in natural coinfection consisted of ascites, fibrinous deposits on internal organs, and increased melanomacrophage centres (MMC) and extensive necrosis in kidneys. Lesions in experimental infection were limited to congestion of internal organs. Enzymatic activity of both extracellular products (ECP) and live cells by well diffusion showed the highest enzymatic index for gelatinase in the ECP of V. harveyi. The enzyme activity evaluated based on the API‐ZYM system revealed the highest activity for alkaline and acid phosphatase in both ECP and bacteria. The MAR index indicated that the pathogens were from a low‐risk region of antibiotic contamination. [ABSTRACT FROM AUTHOR]

Keywords: compensatory growth; Snubnose pompano; stunting; Trachinotus blochii EN compensatory growth Snubnose pompano stunting Trachinotus blochii 403 409 7 12/23/20 20210101 NES 210101 Compensatory growth has been reported in stunted fish by several researchers, and the same has been applied at field level for enhancing the fish production. During stunting phase, the size variation was more prominent in stunted fish than normal fish, whereas it registered a reverse trend during post-stunting phase wherein the size variation was lesser in stunted fish than normal fish. The 90 days stunting study reveals that the growth retarded fish could fully regain the growth when adequately fed, since the final weight and SGR/day % at the end of the poststunting rearing were higher in stunted fish than the normal fish. The FCR at the end of the experiment was slightly higher in the case of 30 days stunted fish, whereas in 60 days stunted fish, it was slightly lower and in 90 days stunted fish it was only half of normal fish (Tables 2-4). [Extracted from the article]

Worldwide, the availability of suitable areas for aquaculture has become a significant concern. In Brazil, the former Ministry of Fisheries and Aquaculture (MPA) has begun to promote discussions and plan meetings on Local Mariculture Development Plans (PLDMs): a planning tool for the establishment of parks and aquatic areas. However, hundreds of groups and individuals still practice aquaculture awaiting a definitive license. This study aimed to serve as a tool to identify suitable sites for the installation of cobia cage farming and also to contribute to the PLDM zoning process. We created 27 criterion maps for marine fish farming. Their individual weights were assigned based on the best judgment of technicians, researchers and other stakeholders using the pair‐wise comparison method. The criteria and their weights were combined using multi‐criteria decision rules, and a final map according to suitability was derived by reclassification. Of the total area, 54,663 ha (14%) were composed of restrictions, and 341,083 ha (86%) were found useful; of which <1% is considered top score. Even so, these are more than enough to ensure the growth of activity. In Rio de Janeiro state, two bays have suitable areas to marine fish culture development. To ensure the sustainability of marine fish farming, we suggested the adoption of limited production areas based on assimilation and production capacity. Through this methodological approach, it was possible to identify suitable areas for cobia farming development. Additionally, the results may serve as a useful tool on which the PLDM can be based on. [ABSTRACT FROM AUTHOR]

Ongoing global warming is one of the major challenges for the development of aquaculture in the tropical regions where species are already cultured in the water temperature close to their upper physiological thresholds. Furthermore, warming can trigger blooms of toxic algae, yet we do not know how extreme warming such as a marine heatwave (MHW) and algal toxins may affect marine aquaculture species. To address this issue, we investigated the effects of a simulated MHW in combination with exposure to trans‐4‐trans‐decadienal (PUA), a diatom‐derived toxin, on survival, growth, development and biochemical composition of cobia larvae and juveniles. Cobia larvae were exposed for 48 hr to one of two temperatures (29 vs. 34°C) and two PUA treatments (0 vs. 0.5 µM). Surviving larvae from each treatment were divided into two subsets: three replicates were used for the feeding test and five replicates were used for the recovery test in a non‐contaminated environment at the respective temperatures of 29 or 34°C. Survival of cobia larvae was reduced by 16% in either MHW or PUA, but it dropped by 60% when both stressors were present, indicating a synergistic effect. MHW, but not PUA, reduced the feeding of cobia larvae. PUA had no delayed effects on growth rate and biochemical composition of the fish. MHW strongly reduced specific growth rate, body protein and lipid contents in cobia. Our results provide the first empirical evidence of how MHW and toxic algae may interact and challenge cobia and marine aquaculture production in tropical countries. [ABSTRACT FROM AUTHOR]

Keywords: embryonic development; hatching; longfin yellowtail; salinity tolerance However, information regarding the effects of specific environmental conditions (e.g. salinity) on the incubation of eggs and yolk-sac larvae of longfin yellowtail is scarce. A one-way analysis of variance ANOVA (trial 1) and two-way ANOVA (spawn sources and salinity; trial 2) were used to compare the effects of salinity on eggs and yolk-sac larvae. [Extracted from the article]

The objective of the present study is to preliminarily clarify the mechanism of carbohydrates metabolism in cobia (Rachycentron canadum) (85 ± 3 g) receiving injection of glucose solution. We examined plasma glucose (GLU), total protein (TP), triglyceride (TG), cholesterol (CHOL), insulin, liver glycogen and muscle glycogen, activities of hepatic hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK), as well as relative expressions of glucose transporter 1 (GLUT1), GLUT2, GLUT3, GLUT4, GLUT5 and GLUT9 in hemocyte, liver and muscle of R. canadum when fish were injected with 200 μl of glucose solution (255 mg/ml) after 0, 1, 2, 4, 8, 12, 24 and 48 hr. Fish received injection of 0.68% saline served as control. Results indicated that the plasma GLU, TG and CHOL increased and reached peak at 1, 8 and 48 hr postinjection (hpi) respectively. The hepatic glycogen increased from 1 hpi, and reached peak at 8 hpi, plasma insulin increased at 1 hpi, and reached peak at 2 hpi, and activity of hepatic PK peaked at 8 hpi. Furthermore, the relative expressions of GLUT1, GLUT2, GLUT3, GLUT4 and GLUT5 in hemocytes reached peak at 1,4, 8, 4 and 8 hpi, respectively, relative expressions of GLUT2, GLUT3, GLUT5 and GLUT9 in liver reached peak at 24, 24, 12 and 24 hpi, respectively, and relative expressions of GLUT1 and GLUT3 in muscle were significantly higher at 2 and 2–4 hpi, respectively compared with those in controls. In conclusion, low ability of utilizing glucose in R. canadum may be attributed to insufficient insulin secretion, low activities of key glycolytic enzymes (HK, PFK and PK) regulated by glucose injection and slow increase of GLUTs. [ABSTRACT FROM AUTHOR]

Juvenile cobia (Rachycentron canadum), a carnivorous fish, was chosen to examine the effects of methionine (Met) supplementation of low fishmeal diets on growth and the expression of key genes related to hepatic lipogenesis and glucose metabolism. Seven isonitrogenous and isolipidic diets were formulated to contain 7.2, 9.0, 10.0, 12.4, 14.1, 16.3 and 18.6 g/kg dietary Met levels. Healthy cobia (initial average weight ± SE = 9.79 ± 0.04 g) were randomly assigned into seven groups in triplicate with 40 individuals per sea cage for 8 weeks. The results showed that the weight gain rate (WGR) of fish increased as the dietary Met was increased up to 12.4 g/kg and then decreased. The expression of insulin‐like growth factor‐I (IGF‐I) and target of rapamycin (TOR) genes was inhibited by the Met‐deficient diets. The mRNA levels of fatty acid synthase (FAS) and sterol regulatory element‐binding protein‐1 (SREBP1) genes increased with increasing dietary Met until 12.4 g/kg after which the former remained constant, whereas the latter decreased from 12.4 to 18.6 g/kg Met. The mRNA levels of pyruvate kinase (PK) increased as the dietary Met levels increased, reaching a peak at 12.4 g/kg, and then decreased with further increases in Met. However, the mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) decreased as the dietary Met was increased up to 12.4 g/kg and then remained constant from 12.4 to 18.6 g/kg Met. In conclusion, based on the straight broken‐line analysis of WGR against dietary Met levels, the optimal dietary Met requirement for juvenile cobia was estimated to be 12.4 g/kg (26.9 g/kg dietary protein). A diet with the optimal level of Met induces fish growth and is associated with increased IGF‐I and TOR. [ABSTRACT FROM AUTHOR]

It is very necessary to clarify the mechanism of carbohydrate metabolism in fish due to their poor ability to utilize carbohydrates. Glucose transporters (GLUTs) are important carriers involved in glucose transport across the plasma membrane, which is the first rate‐limiting step of carbohydrate metabolism. In this study, five glucose transporters (RcGLUT1, RcGLUT2, RcGLUT3, RcGLUT5 and RcGLUT9) were obtained from Rachycentron canadum. The complete cDNAs open reading frames (ORF) of RcGLUT1, RcGLUT2, RcGLUT3, RcGLUT5 and RcGLUT9 were 1,476 bp, 1,530 bp, 1,551 bp, 1,539 bp and 1,578 bp (GenBank accession no. MK560257, MK560258, MH184460, MH184461 and MH184462), encoding 491, 509, 516, 512 and 525 amino acid (aa) residues respectively. All five RcGLUTs contained a Sugar_tr domain, which is an important feature of the GLUT gene family. The multiple sequence alignment and phylogenetic relationship analyses showed that RcGLUTs were highly conserved and homologous from fish to mammals. Examination of tissue distribution showed that RcGLUTs were expressed constitutively in R. canadum. RcGLUT1‐5 and RcGLUT9 had the highest expression in the foregut, kidneys, haemocytes, muscles, liver and heart respectively. All six RcGLUTs first increased to peak levels of expression and then reduced both in the liver and muscle after fasting. The exception is that the expression levels of RcGLUT4 and RcGLUT5 in muscle were significantly lower than the control. In response to hypoxia, only RcGLUT2 in the liver and muscle and RcGLUT9 in muscle were expressed at a significantly lower level relative to the control. In sum, all RcGLUTs in the liver and muscles showed significant changes in response to fasting and hypoxia, suggesting that GLUT genes may play a role in the response to common physiological stresses. [ABSTRACT FROM AUTHOR]

This study determined impacts of dietary methionine concentrations at two temperatures on growth, feeding efficiency and N‐metabolites in juvenile cobia. Methionine concentrations of the experimental diets were deficient (M9; 9 g/kg), sufficient (M12; 12 g/kg) and surplus (M16, 16 g/kg). Water temperature was normal (30°C) or elevated (34°C). Twenty cobia in triplicate tanks were fed the experimental diets for 6 weeks. Both methionine and temperature affected cobia's growth and feeding efficiency. Cobia fed M9 performed lower than the fish fed M12 and M16 diets. Additionally, cobia reared at 34°C performed poorer than at 30°C, probably due to lower voluntary feed intake in the fish reared at 34°C. Protein efficiency ratio and protein productive value in cobia fed M9 diet were less than M12 or M16 diets. This was confirmed with the improved retentions of indispensable amino acids (AAs). No interactions between methionine and temperature were observed in growth and protein accretion. At 30°C, CF improved, while HSI and VSI declined upon methionine supplementation levels. Of which an interaction between temperature and methionine was present. Plasma, muscle and liver free AA and N‐metabolites were affected by methionine and temperature. Furthermore, temperature affected cobia's lipid class composition, resulting in increased phospholipids and cholesterol at 34°C. [ABSTRACT FROM AUTHOR]

Summary: The reproductive biology of cobia, Rachycentron canadum, from the coastal waters of Dungun, Malaysia was studied from June 2014 to May 2015. From commercial trawls, a total of 201 samples (combined sexes) were collected (fork lengths [FL] 37.5–124.0 cm; body weights 0.5–20.4 g). The overall sex ratio of females to males was 1:0.9, which was not significantly different (χ2 = 2.12, df = 1; p < .05). Estimations of length at 50% maturity (L50) showed that both sexes matured at approximately 75 cm FL; estimated spawning frequency was 6 days. Mean batch fecundity (BF) ranged from 0.55 to 4.32 million eggs. The average number of eggs per gram of ovary was from 2,100 to 5,400 eggs, and relative fecundity 147 eggs/g. There was a weak positive correlation (r2 = .48) between BF and female FL as well as BF with an ovary‐free body weight (r2 = .56), possibly due to females being in a continuous spawning condition and some possibly half‐spent, based on the histological examination of the female gonads. Despite cobia being asynchronous spawners, the gonadosomatic index in both males and females showed peaks in June, November, and particularly March. Based on histological examination, spawning‐capable males were encountered throughout the study period, whereas spawning‐capable females in the late developing subphase were found mostly in March and April. This is the first study on the reproductive aspects of cobia in Malaysian waters. [ABSTRACT FROM AUTHOR]

A shrimp protein hydrolysate ( SPH) containing 894.2 g kg−1 crude protein ( CP) and 54.3 g kg−1 total lipids was tested as a partial replacement for fish meal ( FM) in diets of juvenile cobia. The effects of increasing dietary levels of SPH on the survival, weight gain ( WG), specific growth rate ( SGR), feed conversion ratio ( FCR), nitrogen retention efficiency ( NRE) and daily feed intake ( DFI) of cobia with initial body weight of 11.9 g were evaluated. Four isoproteic (from 431.1 to 439.7 g kg−1) and isoenergetic (20 825-21 347 MJ kg−1) diets were formulated to contain 0 (Control), 120, 240 or 360 g kg−1 of dietary CP derived from SPH. Survival, WG, SGR, FCR, NRE and DFI ranged from 90 to 100%, 40.2-56.5 g, 4.7-6.1% day−1, 1.04-1.54, 26.3-44.0% and 4.7-6.0% fish−1 day−1 respectively. Survival and DFI were not affected by the dietary treatments. On the other hand, fish fed the control diet and the one containing 120 g kg−1 SPH had higher WG, SGR and FCR. Nitrogen retention efficiency was significantly higher for fish fed diets 0 and 120. It is concluded that up to 120 g kg−1 of SPH in cobia diets can be used with no significant effects on feed utilization and fish performance. [ABSTRACT FROM AUTHOR]

This study was conducted to compare the effects of manganese sulphate (Mn-S), glycine manganese(Mn-Gly) and manganese 2-hydroxy-4-(methylthio)butyrate (Mn- HMB) on juvenile cobia, Rachycentron canadum L. Treatments consisted of 0, 2, 4, 8, 16 or 32 mg supplemental Mn kg−1 from Mn-S, Mn-Gly or Mn- MHB. Growth performance, manganese status, antioxidant activities and tissue mineral content were analysed after a 70-day feeding period. Specific growth rate ( SGR) increased with feeding 6.29 to 12.65 mg Mn kg−1 diet from the Mn-S or 6.86 to 12.39 mg Mn kg−1 from the Mn-Gly or 6.50 to 8.33 mg Mn kg−1 from the Mn- HMB and then plateaued above these levels. Feed conversion ratio ( FCR) show decreasing first and then increased trend. Survival rate ( SR) were not affected by the dietary treatments ( P > 0.05). Fish fed diets supplemented with manganese at levels of 4-32 mg Mn kg−1 had obviously higher hepatic Mn- SOD activity ( P < 0.05); on the contrary, hepatic has lower malondialdehyde ( MDA) content ( P < 0.05) than fish fed the basal diet. The manganese concentrations of whole body and vertebrae increased with increasing dietary Mn levels from 2-32 mg Mn kg−1 (independent on manganese sources). Dietary Mn supplementation did not significantly influence the copper concentrations of whole body and vertebrae, the zinc concentrations of whole body and liver. Analysis by the broken-line regression of SGR indicated that the optimal dietary Mn requirements in juvenile cobia were 15.42, 11.22 and 10.50 mg Mn kg−1 diet from Mn-S, Mn-Gly or Mn- HMB respectively. [ABSTRACT FROM AUTHOR]

Fish are potentially submitted to water acidification when reared in recirculating aquaculture systems. This study evaluated the responses of juvenile cobia Rachycentron canadum after acute exposure to acid water. Juvenile cobia (12.6 ± 0.5 g; 14.2 ± 0.2 cm) were acutely exposed to four pH levels (7.9 (control), 6.5, 6.0, and 5.5). After 24 h of exposure to different pH values, fish were sampled for physiological and histopathological evaluation. Acid water affected physiological parameters and induced morphological histopathologies on gill and skin of juvenile cobia, and these effects were more conspicuous with decreasing pH values. Acid stress induced blood acidosis in juvenile cobia, coupled to a decrease in bicarbonate ( HCO3−) and saturated O2 (s O2) in fish blood. On the other hand, haematocrit, haemoglobin and glucose concentration increased their values ( P < 0.01) comparing to control level. Hyperplasia with completely fusion of secondary lamella was observed in all pH treatments (6.5. 6.0 and 5.5), while telangiectasia and proliferation of chloride cells were present for fish exposed to pH 6.0 and 5.5. In skin hyperplasia and hypertrophy of mucous cells, necrosis of these cells for fish exposed to pH 6.0 and 5.5 was observed. The results of this study demonstrate that acute acid water exposition affected physiology and histopathology in juvenile cobia, especially at pH values below 6.5. Accordingly, particular attention must be given to pH during cobia reared in recirculating aquaculture. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the effects of the immunostimulant combination ( IC) containing β-glucan, A3α-peptidoglycan, vitamin C and vitamin E on the growth performance, non-specific immunity and protection against Vibrio harveyi infection in cobia ( Rachycentron canadum). Fish were fed diets containing six graded levels of IC (0, 1, 2, 3, 4 and 5 g kg−1 diet) for 8 weeks. The results showed that the survival rate ranged from 81.1 to 84.4% with no significant difference among all the groups ( P > 0.05) after the feeding experiment. Dietary IC significantly increased the specific growth rate ( SGR), serum lysozyme, alternative complement pathway ( ACH50) activity, phagocytosis percentage ( PP) and respiratory burst activity of head kidney macrophages of cobia. Moreover, feeding of supplemented diets containing 3.0 g kg−1 IC resulted in significantly lower mortality against the pathogens, V. harveyi compared with the control group. To elevate the growth and immune resistance ability of cobia, the optimal dose of dietary IC administration, determined by second-order polynomial regression analysis was 3.43 and 2.71 g kg−1 diet, respectively, on the basis of the SGR and mortality after challenge with V. harveyi. [ABSTRACT FROM AUTHOR]

This study investigates the effects of four predominant constituent fatty acids of fish oils, including palmitic acid (16:0, PAM), oleic acid (18:1n-9, OLA), eicosapentaenoic acid ( EPA, 20:5n-3) and docosahexaenoic acid ( DHA, 22:6n-3), on cell differentiation and lipid accumulation in the primary culture of cobia preadipocytes. Time-serial (0-20 days) comparisons of the changes in the expression of relevant genes and late-stage (Day 20) adiposity including lipid droplet size and lipid accumulation of the differentiating preadipocytes were also studied. Lipid accumulation was significantly higher when adipocytes were incubated with OLA compared to EPA and DHA and with DHA compared to EPA. Although the expressions of transcription factors C/ EBPβ and PPARγ were significantly higher when treated with EPA than with DHA in the early stage (Day 4), the lipogenic genes FABP1, FATP2 and LPL were equally upregulated. The upregulation by EPA was greater than that by DHA in the late stage (Day 20). Among the fatty acids studied, OLA, which is also abundant in plant oils such as olive or canola oil, was most adipogenic. Although both EPA and DHA were antiadipogenic, EPA was more adipogenic than DHA. [ABSTRACT FROM AUTHOR]

The effects of NaCl supplementation (0.0%, 2.5%, 5.0%, 7.5% and 10.0% dry weight of a basal diet) on growth, gill histological alterations and osmoregulation of juvenile cobia reared in low-salinity water (5 g L−1) were assessed. At the end of the experiment, gills were sampled for Na+, K+- ATPase activity determination and histological evaluation. In all treatments, no mortality was observed. Results showed that dietary NaCl supplementation did not alter growth. At the highest supplementations (7.5% and 10.0%), juvenile cobia showed higher feed intake and feed conversion ratio. Na+, K+- ATPase activity was higher in fish fed the diet without salt supplementation than in those fed with NaCl-supplemented diets. The number of chloride cells significantly increased with increasing dietary salt level, being 2.5-fold higher in fish fed with 10.0% NaCl supplementation (41 cells mm−2) than in those from the non-supplemented fed group (16 cells mm−2). These findings indicate that dietary salt supplementation stimulated chloride cell proliferation paralleled with a reduction in the gill Na+, K+- ATPase activity, suggesting a possible decrease in energy consumption associated with osmoregulation. However, the suggested energy sparing did not have a significant impact on juvenile cobia growth. [ABSTRACT FROM AUTHOR]

Cobia (8.4 ± 0.1 g body weight) were fed to satiation with three test diets of high plant protein-based ingredients and different lysine to arginine ratios, and one commercial diet (currently used for cobia rearing in Vietnam as a control for growth) for 6 weeks. The test diets contained 206 g marine ingredients kg−1, including fishmeal, krill meal and fish protein concentrate (in order of high to low inclusion), while the rest of the dietary protein was a blend of soya and pea protein concentrate, wheat protein and sunflower meal. Crystalline lysine and arginine were added in the test diets to produce either a balanced lysine to arginine ratio ( BL/ A; 1.1) and a high or low lysine to arginine ratio ( HL/ A; 1.8 and LL/ A; 0.8, respectively). There were no significant differences in final body weight, weight gain, feed conversion ratio or protein gain between cobia fed BL/ A- and commercial control diet ( CCT). Cobia fed BL/ A diet performed better than fish fed either HL/ A- or LL/ A diet. This was partly due to a higher feed intake and protein and lipid gain in cobia fed BL/ A diet as compared to HL/ A- and LL/ A diet. [ABSTRACT FROM AUTHOR]

The present study was carried out to investigate the number of daily feeding sessions that results in maximum growth of juvenile cobia under laboratory conditions. Groups of eight fish (110 g) were randomly distributed in twenty 500-L tanks and hand-fed a commercial diet for 60 days. The same amount of feed was offered daily, divided in 1, 2, 3, four or six meals. None of the parameters associated with growth performance (survival, weight gain, specific growth rate, feed intake, condition factor or size variation) showed any significant differences among treatments. Although under the present conditions feeding frequency had no effect on the growth performance of cobia larger than 110 g, in commercial farming operations where large numbers of fish are kept within a single rearing structure, fish may have aggressive interactions during feeding. Under these conditions, it is difficult to ensure that all cobia are fed to satiation and thus it is usual to provide two or more meals per day. The present results indicate that for an individual cobia the provision of more than one daily meal has no significant effect on growth performance. [ABSTRACT FROM AUTHOR]

Cytosine-guanine oligodeoxynucleotide (CpG ODN) motifs of bacterial DNA are recognized through toll-like receptor 9 (TLR9) and are potent activators of innate immunity. However, the interaction between TLR9 and CpG ODN in aquatic species has not been well characterized. Hence, cobia TLR9 isoform B (RCTLR9B) was cloned and its expression and induction in intestine were investigated. RCTLR9B cDNA consists of 3113bp encoding 1009 amino acids containing three regions, leucine rich repeats, transmembrane domain, and toll/interleukin-1 receptor (TIR) domain. Intraperitoneal injection of CpG ODN 2395 upregulated RCTLR9 A and B and MyD88 and also induced the expressions of Mx, chemokine CC, and interleukin IL-1β. Cobia intraperitoneally injected with CpG ODN 1668 and 2395 had increased survival rates after challenge with Photobacterium damselae subsp. piscicida. In addition, formulation of CpG ODN with formalin-killed bacteria (FKB) and aluminum hydroxide gel significantly increased expressions of RCTLR9 A (50 folds) and B (30 folds) isoforms at 10 dpi (CpG ODN 1668) and MyD88 (21 folds) at 6 dpv (CpG ODN 2395). Subsequently, IL-1β increased at 6 dpv in 1668 group. No histopathological damage and inflammatory responses were observed in the injected cobia. Altogether, these results facilitate CpG ODNs as an adjuvant to increase bacterial disease resistance and efficacy of vaccines in cobia. [ABSTRACT FROM AUTHOR]

A 9-week feeding trial was conducted to estimate the dietary requirement of arginine in juvenile cobia in indoor flow-through and aerated aquaria. Six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of arginine ranging from 1.76% to 3.75% (dry weight) at about 0.4% increments replaced by equal proportions of glycine. Survival was not significantly different among dietary treatments. Specific growth rate ( SGR) and feed efficiency ratio ( FER) increased with increasing dietary arginine up to the 2.96% diet ( P < 0.05), and thereafter declined. The whole body crude protein content was significantly affected by dietary arginine ( P < 0.05), while moisture, crude lipid and ash showed no significant differences among dietary treatments. The essential amino acid contents of muscle were not significantly affected by dietary arginine. The serum nitric oxide synthase activities in fish fed diets with arginine from 2.18% to 3.75% were significantly higher than activities in fish fed the diet with 1.76% arginine ( P < 0.05). On the basis of SGR and FER, the optimal dietary arginine requirements of juvenile cobia were estimated to be 2.85% of the diet (6.20% of dietary protein) and 2.82% of the diet (6.13% of dietary protein), respectively, using second-order polynomial regression analysis. [ABSTRACT FROM AUTHOR]

An 8-week experiment was designed to determine the optimum dietary iron requirement of juvenile cobia Rachycentron canadum (mean initial weight, 15.89 ± 0.84 g) with iron sulphate (Fe SO4•7H2O) and iron methionine (FeMet) as iron sources, using a semi-purified diet based on casein and white fish meal as the protein sources. The basal diet was supplemented with 0, 30, 60, 120, 240 and 480 mg iron kg−1 dry diet from either Fe SO4 or FeMet, respectively. Survival was not significantly affected by the all dietary treatment. Weight gain ( WG), feed efficiency ( FE), serum catalase activity ( SCAT), and haemoglobin were significantly affected by any of the dietary treatments from both of two iron sources. Based on broken-line regression analysis of WG, FE and SCAT, a minimum requirement for dietary iron was recommended to be 80.5-94.7 mg kg−1 from Fe SO4 and 71.3-75.1 mg kg−1 from FeMet. Iron supplement to the basal diet had no significant effect on haematocrit, erythrocyte count, iron concentration in whole body and fillet. Our experiment also showed that the bioavailability of FeMet and Fe SO4 to juvenile cobia was similar for WG and FE, and the relative bioavailability of FeMet and Fe SO4 to juvenile cobia was 275% for maximum SCAT. [ABSTRACT FROM AUTHOR]

A 10-week feeding trial was conducted to estimate the optimum dietary manganese requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 501 g kg−1 crude protein from vitamin-free casein, gelatin and fish protein concentrate. Manganese sulphate was added to the basal diet at 0 (control group), 6, 12, 18, 24 and 36 mg Mn kg−1 diet providing 5.98, 7.23, 16.05, 23.87, 28.87 and 41.29 mg Mn kg−1 diet, respectively. Each diet was randomly fed to three replicate groups of cobia for 10 weeks, and each tank was stocked with 30 fish (initial weight, 6.27 ± 0.03 g). The manganese concentration in rearing water was monitored during the feeding period and was < 0.01 mg L−1. Dietary manganese level significantly influenced survival ratio ( SR), specific growth ratio ( SGR), feed efficiency ratio ( FER) and the manganese concentrations in the whole body, vertebra and liver of cobia. When the dietary manganese level rose from 5.98 mg kg−1 to 23.87 mg kg−1, the superoxide dismutase ( SOD; EC 1.15.1.1) activities in liver also increased ( P < 0.05). But there was no significant change in SOD activities for the groups fed with diets containing manganese level higher than 23.87 mg kg−1. On the basis of broken-line regression of SGR, manganese concentration in whole body and vertebra the manganese requirements of juvenile cobia were 21.72 mg kg−1, 22.38 mg kg−1 and 24.93 mg kg−1 diet in the form of manganese sulphate, respectively. [ABSTRACT FROM AUTHOR]

The effects of replacing fish meal (FM) with shrimp waste meal ( SWM) in diets fed to juvenile cobia ( Rachycentron canadum) were investigated through a 6-week trial. SWM was added to replace FM at fractions of 0%, 10%, 20% and 25% of the diet. The result showed the survival rates of the fish were higher than 86.7%. The weight gain and feed conversion rate showed an increasing trend as the SWM proportion in diet increased from 0% to 25%, but the protein efficiency ratio showed a decreasing trend in efficiency. In addition, the hepatosomatic index increased significantly when the SWM percentage was 20% and 25%. There were no significant differences in the protein and ash concentration of the muscle among all dietary groups. However, the muscle lipid content was low when fish fed in diets with high SWM level. Chitinase activity was extremely high in the pyloric caeca tissue of cobia, and increased specific activities of chitinase were only found in the foregut of cobia fed diets containing 10% SWM for a 6-week period. A challenge test showed that SWM could not enhance cobia resistance to Photobacterium damselae ssp. piscicida infection. Our results suggest that the administration of a 10% SWM diet could potentially reduce the use of FM in the diet of cobia. [ABSTRACT FROM AUTHOR]

Cobia, Rachycentron canadum (500 g) cultured in pond cages for a 3-month experiment were fed two moist diets based on raw fish with or without added fish silage. No significant differences in nutritional composition were observed between the fillet groups, which were of high quality with a balance of essential and non-essential amino acids ( EAA/ NEAA = 1) and medium levels of omega-3 fatty acid composition (210 g kg−1 total fatty acids). The total quality index method and quantitative descriptive analysis from both groups were correlated throughout storage ( r2 = 0.83-0.86). After 15 days iced storage, the scores of most attributes were low compared to maximum accepted values. The thiobarbituric acid reactive substances and microbial counts were also below the accepted limits after the storage trial. It might be concluded that the nutritional composition and the fillet quality were similar for the groups fed raw fish with or without added fish silage, and the estimated shelf life for cobia was >15 days. [ABSTRACT FROM AUTHOR]

An 8-week feeding trial was conducted to establish the dietary vitamin E requirement of juvenile cobia. The basal diet was supplemented with 10, 20, 30, 40, 60, 120 mg vitamin E kg−1 as all-rac-α-tocopheryl acetate. The results indicated that fish fed the diets supplemented vitamin E had significantly higher specific growth rate, protein efficiency ratio, feed efficiency and survival rate than those fed the basal diet. It was further observed that vitamin E concentrations in liver increased significantly when the dietary vitamin E level increased from 13.2 to 124 mg kg−1. Fish fed the basal diet had significantly higher thiobarbituric acid-reactive substances concentrations in liver than those fed the diets supplemented vitamin E. Fish fed the diets supplemented with 45.7 and 61.2 mg kg−1 vitamin E had significantly higher red blood cell and haemoglobin than those fed the basal diet, while fish fed the diets supplemented with 61.2 and 124 mg kg−1 vitamin E had higher immunoglobulin concentration than those fish fed the basal diet. Lysozyme and superoxide dismutase were significantly influenced by the dietary vitamin E level. The dietary vitamin E requirement of juvenile cobia was established based on second-order polynomial regression of weight gain and lysozyme to be 78 or 111 mg all-rac-α-tocopheryl acetate kg−1 diet, respectively. [ABSTRACT FROM AUTHOR]

Year-round control of the spawning cycle of cobia ( Rachycentron canadum) has been established by using water temperature manipulation. To compare the effectiveness of using this method to induce volitional spawning in cobia, two 80 m3 recirculating aquaculture systems ( RAS) were used. Temperatures in one of the maturation tanks ('Mat 1') were maintained between 27 and 29°C for 12 months of the 15.5-month study period. Temperatures in the second maturation tank ('Mat 2') were allowed to fluctuate naturally throughout the year and ranged from 20 to 32°C. A total of 101 spawning events occurred in the tanks between the spring of 2008 and the summer of 2009 (3 April 2008 to 17 June 2009). Of the 38 total spawning events in Mat 1, 17 of them (44.7% of all Mat 1 spawning events) occurred during the off-season (fall and winter). The egg viability rates did not differ significantly ( P > 0.05) between on- and off-season spawns in Mat 1. Conversely, cobia broodstock exposed to natural water temperatures (no environmental manipulation) in Mat 2 followed the natural pattern of warm water (>26°C) dependence, limiting egg production to spring and summer seasons. This method of water temperature manipulation allows for effective control of the cobia reproductive cycle without compromising egg viability. [ABSTRACT FROM AUTHOR]

The present study was performed to investigate the effects of a commercially available probiotic product (compound probiotic) containing Bacillus subtilis 7.0 × 109 CFU g−1, Bacillus licheniformis 3.0 × 109 CFU g−1, Lactobacillus spp. 5.0 × 108 CFU g−1 and Arthrobacter spp. 1.0 × 108 CFU g−1 on the growth performance, non-specific immunity and protection against Vibrio harveyi infection in cobia ( Rachycentron canadum). Fish were fed diets containing six graded levels of compound probiotic (0.0, 1.0, 2.0, 3.0, 4.0 and 5.0 g kg−1) for 8 weeks. The results showed that the survival rate ranged from 81.1% to 84.4% with no significant difference among dietary treatments ( P > 0.05) after feeding experiment. Dietary compound probiotic significantly increased the specific growth rate (SGR), serum lysozyme, alternative complement pathway (ACP) activity, phagocytosis percentage (PP) and respiratory burst activity of head-kidney macrophages of cobia. Moreover, feeding of supplemented diets containing compound probiotic resulted in significantly lower mortality against the pathogens Vibrio harveyi compared with the control group. To elevate the growth and immune resistance ability of cobia, an optimal dose of dietary compound probiotic administration determined by second-order polynomial regression analysis was 3.3 g kg−1, on the basis of the SGR and mortality after challenge with V. harveyi. [ABSTRACT FROM AUTHOR]

A 9-week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition and apparent digestibility coefficient and digestive enzyme activities of juvenile cobia. Six isonitrogenous and isolipidic diets containing graded levels of starch (1.3%, 6.5%, 12.5%, 18.4%, 24.2% and 30.4%) were fed to juvenile cobia. Specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary starch up to 18.4% ( P<0.05), and thereafter SGR declined but FER and PER remained nearly the same. Apparent digestibility coefficient of starch reduced significantly when dietary starch up to 30.4%. Fish fed the diets with starch from 18.4% to 30.4% showed higher amylase activities in intestinal tract than those fed diets containing starch 1.3% and 6.5% ( P<0.05). Significantly higher whole-body lipid contents were observed in fish fed the diets containing higher starch. Whole-body moisture content was inversely correlated with whole-body lipid content, while protein and ash showed no significant differences. Plasma glucose, hepatosomatic index, liver glycogen and liver lipid increased with an increasing dietary starch. Based on SGR and FER, the appropriate dietary starch supplementations of juvenile cobia were estimated to be 21.1% and 18.0 % of diet respectively. [ABSTRACT FROM AUTHOR]

As a marine carnivore exhibiting exceptionally high growth rates, cobia are considered a species for which fish oil (FO) replacement may be difficult. However, partial, if not complete, FO replacement is necessary to ensure sustainability. We evaluated the effects of graded substitution of dietary FO with soybean oil (SO) in cobia culture. Feeds contained FO (100% FO), SO (0% FO) or blends of the two (67% FO, 33% FO) as the supplemental lipid source. Production performance was largely unaffected by partial replacement of FO with SO: feed intake and final weight were reduced only in the 0% FO dietary treatment. Fillet total lipid fatty acid (FA) composition differed among the dietary treatments, closely approximating dietary FA profile. As increasing amounts of FO were replaced, SO-associated FA became enriched within the fillet lipid at the expense of FO-associated FA. Fillet lipid classes were associated with a particular FA signature, regardless of dietary FA profile. SO can replace a substantial amount of dietary FO; however, juvenile cobia appear to exhibit a nominal requirement for intact long-chain polyunsaturated FA. Therefore, aggressive FO replacement may result in essential fatty acid deficiencies unless the feeds can be amended with alternative sources of these essential nutrients. [ABSTRACT FROM AUTHOR]

Juvenile cobia ( Rachycentron canadum) (100 g) were fed four moist diets (447-476 g kg dry wt) where 0, 130, 260 or 390 g kg of concentrated lizardfish ( Saurida undosquamis) silage replaced fresh lizardfish, respectively. Blood and livers were sampled at 0, 6, 12, 24 and 48 h postfeeding at the end of the 3-week experiment. At 6 h postfeeding in all groups, maximum concentrations of most plasma essential amino acids were observed, while significantly lower levels of most non-essential amino acid levels were recorded compared to the other sampled times. At 6 and 12 h after feeding, the concentration of most plasma free amino acid (FAA) increased with an increase in dietary fish silage levels. Most FAA in livers of all groups peaked at 12 and 24 h postfeeding. However, at 48 h postfeeding, concentrations of most plasma FAA were significantly higher in fish fed 0% silage-based diet than in fish fed the other diets (4999 versus 3390-4339 nmol AA mL plasma). Growth rates and feed utilization were significantly lower in cobia fed 26% or 39% silage-based diets than in fish fed 0% or 13% silage-based diets. Different levels of silage protein thus seemed to have effects on growth and feed utilization efficiency of juvenile cobia. Results from this study support the premise that fish silage can be included until 130 g kg in cobia diets. [ABSTRACT FROM AUTHOR]

An 8-week feeding trial was conducted to evaluate the effect of dietary carbohydrate sources on the growth performance and hepatic carbohydrate metabolic enzyme activities of juvenile cobia. Six experimental diets were formulated to contain 20% glucose, sucrose, maltose, dextrin, corn starch and wheat starch respectively. The results indicated that fish fed the wheat starch and dextrin diets showed significantly better weight gain, specific growth rate and protein efficiency ratio compared with those fed the other diets. However, fish fed the glucose diet had a significantly lower survival and condition factor than those fed the other diets. There were significant differences in the total plasma glucose and triglyceride concentration in fish fed diets with different dietary carbohydrate sources. Haematocrit, haemoglobin, red blood cell and leucocytes were significantly affected by the dietary carbohydrate sources. The activities of glucose-6-phosphate dehydrogenase (G6PD), 6-phosphofructokinase (PFK) and fructose-1,6-bisphosphatase (FBPase) were significantly affected by the dietary carbohydrate sources, while fish fed the glucose diet showed higher G6PD, PFK and FBPase activities than those fed the other diets. These data indicated that dextrin and wheat starch were the most optimal carbohydrate sources for juvenile cobia. [ABSTRACT FROM AUTHOR]

A 10-week feeding trial was conducted to determine the optimal requirement of cobia ( Rachycentron canadum Linneaus) for dietary ascorbic acid (AA). Graded levels of L-ascorbyl-2-polyphosphate (LAPP) were supplemented in basal diet to formulate six semi-purified diets containing 2.70 (the control diet), 8.47, 28.3, 80.6, 241 and 733 mg AA equivalent kg diet, respectively. Each diet was randomly fed to triplicate groups of fish in flow-through plastic tanks (300 L), and each tank was stocked with 25 fish with average initial weight of 4.59 ± 0.36 g. Observed deficiency signs included poor growth, higher mortality and lower feeding rate (FR) in the fish of the control group. Fish fed the control diet had significantly lower weight gain (WG), lower feed efficiency ratio (FER) and lower tissue AA concentrations in fish liver and muscle. With the increase of dietary AA, the survival, WG, FER, hepatic and muscular AA concentrations of cobia significantly increased and then levelled off. The dietary AA requirement of cobia was estimated to be 44.7 mg kg based on WG, 53.9 mg kg or 104 mg kg based on either hepatic or muscular AA concentration, respectively. [ABSTRACT FROM AUTHOR]

Optimization of the protein to energy ratio in juvenile cobia ( Rachycentron canadum) would allow the production of diets that maximize growth without the addition of excess energy that may increase costs or even be detrimental to the health of the fish. During a 6-week growth trial, juvenile cobia (5.6 ± 0.5 g fish−1 initial weight) were fed five isonitrogenous and isolipidic diets containing various protein to energy ratios using starch as the energy source. At the end of the trial, some fish were analysed for body composition characteristics while the rest were used to examine the excretion of dietary starch in the feces. Survival and growth were not significantly affected, but feed efficiency (ranging from 0.64 to 0.94) and daily consumption (ranging from 45.3 to 64.1 g kg−1 of body weight d−1) were affected. No reduction in consumption due to excess energy was noted. Analysis of the fecal carbohydrate data showed a linear relationship between dietary inclusion and excretion of carbohydrates with no sign of reaching saturation. Results of this study suggest that cobia can utilize dietary carbohydrates up to at least 340 g kg−1 of dry diet with an optimal protein to energy ratio of approximately 34 mg protein kJ−1metabolizable energy. [ABSTRACT FROM AUTHOR]

A 10-week feeding trial was conducted to estimate the optimum dietary selenium (Se) requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 50.6% crude protein from vitamin-free casein, gelatin. A control diet (no added seleno-dl-methionine) and five experimental diets containing 0.20, 0.40, 0.60, 0.80 and 1.00 mg seleno-dl-methionine kg−1 were prepared. Each diet was randomly fed to triplicate groups of juvenile cobia with initial weight 6.27±0.03 g in a flow-through system. The Se concentration in rearing water was monitored during the feeding period, and was not detectable. The dietary Se level significantly influenced the survival, specific growth rate (SGR), feed efficiency and the Se concentrations in the whole body and vertebra of cobia. The Se-dependent glutathione peroxidase (EC 1.11.119) activity increased with an increase in the dietary Se levels ( P<0.05). Hepatic glutathione reductase (EC 1.6.4.2) activity was the highest in fish fed the diet with 0.21 mg Se kg−1, and declined with an increase in the dietary Se levels. Based on broke-line regression of SGR, the Se concentration in the whole body and vertebra, the Se requirements of juvenile cobia were 0.788, 0.811 and 0.793 mg Se kg−1 diet in the form of seleno-dl-methionine respectively. [ABSTRACT FROM AUTHOR]

The study was conducted in Cam Ranh, Vietnam, in 1000-L tanks supplied with recirculated and biofiltered saltwater (33‰ and 28.4 °C) to evaluate the potential use of lizard fish ( Saurida undosquamis) or blue crab ( Portunus pelagicus) acid silage protein for juvenile cobia (23–25 g). Six isoenergetic test moist diets (4915–5125 kcal kg−1), using either raw fish diet, fish silage diet (FSD), raw crab diet, crab silage diet (CSD), mixed raw fish/raw crab diet or mixed fish/crab silage diet (MSD), as part of the protein sources in the steam-cooked diets, were fed to satiety to triplicate groups of 20 fish each for a 6-week growth trial. Y2O3 was added as an inert indicator to determine the apparent digestibility coefficients (ADC) for macro nutrients and gross energy. Weight gain (185–286%) and specific daily growth rate (2.5–3.2% per day) were significantly higher in cobia fed the raw-based diets and FSD than in fish fed CSD and MSD (34–90 and 0.7–1.5% per day). Feed conversion ratios (FCR) were significantly higher in the groups fed CSD and MSD diets (2.1–6.5) than the groups fed the other diets (1.0–1.2), resulting in significantly lower protein productive values (0.1–0.2) in the groups fed CSD and MSD than in the other groups (0.3–0.4). The FCR results were confirmed by significantly lower ADC values in fish fed CSD and MSD than those in fish fed the other diets. We thus conclude that the present raw-based diets were better utilized by juvenile cobia than silage-based diets, particularly the diet made from crab silage. [ABSTRACT FROM AUTHOR]

The article focuses on the application of a microdiet in rearing of larvae of cobia Rachycentron canadum. The larvae were reared in 70 L plastic tanks with slight aeration. On average food was supplied four times daily. Debris and dead fish were taken out from the containers daily. About 50% of the tank water was replaced with fresh- filtered seawater.

Cobia culture has been rapidly gaining in popularity since the early 1990s; however, the relative success of modified commercial diets in aquaculture has delayed the need for specific research into the nutritional requirements of cobia. Recent work has determined optimum dietary protein and lipid levels in juvenile cobia at 45 and 5–15% dry weight respectively. Maximum growth and feed conversion ratios have been recorded at 27–29 °C in juvenile cobia with an optimum ration level determined at 9% initial body weight per day. There is limited information on amino acid and essential fatty acids (EFA) requirements in cobia. Several studies have explored alternate protein sources in juvenile cobia with relative success observed with meat meal, yeast-based protein and various plant based sources including soybean meal. There is no literature on the vitamin or mineral requirements of cobia or the nutritional requirements of larger fish. Therefore future research should focus on the amino acid, EFA, vitamin and mineral requirements of cobia while the protein, lipid and energy requirements of larger cobia should be addressed. Additional work on feed ingredients, choice and palatability would also aid in maximizing culture production while minimizing costs thereby producing a more sustainable product. [ABSTRACT FROM AUTHOR]

An experiment was conducted in the laboratory to investigate the effects of additive ratios of docosahexaenoic acid (DHA) to eicosapentaenoic acid (EPA) on the growth and survival of cobia ( Rachycentron canadum) juveniles from August to October 2005. Three hundred and eighty cobia juveniles (56 days of age, body weight 6.9 ± 0.1 g, body length 9.2 ± 0.1 cm) were selected and 20 of them were freely taken for initial sample analysis in the week 0. Additional 360 juveniles were randomly assigned into eight groups with triplicate, total 24 tanks with 15 fish each. Cobia juveniles were reared in glass-steel tanks (200-L volume per tank) using filtered seawater with temperature 26–30.5 °C, salinity 25.4–33.0 g L−1 and pH 7.8–8.0. Cobia juveniles were fed for 8 weeks using seven treatment diets (D-1 to D-7) with the same amount of DHA and EPA (15.0 ± 1.2 g kg−1 of dried diet), but varying ratios of DHA to EPA (0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, respectively) and a control diet (D-0, DHA + EPA = 8.0 g kg−1 of dried diet, DHA/EPA = 1.3). Five juveniles per tank were randomly taken for sample analysis at the end of weeks 4 and 8, respectively. The highest protein efficiency rate (PER; 1.5 in mean), average body weight (BW; 73.3 g per fish in mean) and the lowest feed conversion ratio (FCR; 1.6 in mean) were obtained in cobia juveniles fed the control diet at the end of week 8. These parameters were significantly different ( P < 0.05) among juveniles fed the control and treatment diets; however, no significant difference ( P > 0.05) was found among juveniles fed the treatment diets evaluated in this study. It was concluded that the survival and growth of cobia juveniles were not greatly influenced by additive ratios of DHA to EPA in our experimental conditions. [ABSTRACT FROM AUTHOR]

Six experiments were designed to determine the optimal anaesthetic dosage of tricaine methanesulphonate (TMS) and clove oil that could be used safely on juvenile cobia Rachycentron canadum of two sizes [G1=4.9±0.8 g; G2=13.9±3.1 g]. We documented the stage of anaesthesia and the acute toxicity as 96 h LC50 (lethal concentration 50% population) at various exposure times of the two anaesthetics. At 10 min induction time, the TMS 96 h LC50 was 93.9 mg L−1 in G1 and 97.0 mg L−1 in G2. Compared with clove oil, the 96 h LC50 was 60.0 mg L−1 in G1 and 69.8 mg L−1 in G2. The difference between the two groups (G1, G2) did not influence anaesthesia safety ( P>0.05). Rachycentron canadum achieved stage 3 anaesthesia more rapidly at a lower clove oil concentration level (40 mg L−1, 10 min) than TMS (60 mg L−1, 10 min), but the recovery period of clove oil, was significantly longer. Clove oil was the most effective in reducing the short-term stress induced by routine biometry (20 mg L−1, 10 min) and also by transporting (1 mg L−1, 8 h). Whereas, for long-term exposure, 40 mg L−1 TMS was found to be safe. [ABSTRACT FROM AUTHOR]

This experiment was conducted to evaluate the effect of different levels of dietary phospholipid (PL) on growth, survival and nutrient composition of 25 days posthatch cobia Rachycentron canadum (0.4 g initial wet weight). For 42 days, fish were fed fish meal and protein hydrolysate based diets containing four PL levels (0, 20, 40 and 80 g kg−1dry matter: purity 97%) and phosphatidylcholine purity was 60%. All diets were isonitrogenous and isolipidic by regulating the fish oil and maize oil levels. Weight gain (2601–10892%), specific growth ratio (7.82–11.18) and survival (49–100) were significantly affected by dietary PL. Intraperitoneal fat ratio (0.19–0.74) and hepatosomatic index (2.67–3.08) increased with dietary PL level. The effect of dietary PL levels on the chemical composition of tissues was significant only for whole body and liver. The contents of plasma total cholesterol (2.47–3.77 mmol L−1) and PL (1.03–2.97 mmol L−1) increased with an increase in dietary PL. In conclusion, in our study survival and growth continued to increase even at the highest PL levels used (80 g kg−1); therefore optimal dietary PL levels may well exceed 80 g kg−1 for early juvenile cobia requirement. It also indicated from the experiment that PL could affect lipid deposition and resulted in a higher lipid level in fish tissue. [ABSTRACT FROM AUTHOR]

This paper describes advances in hatchery and grow-out technology of cobia ( Rachycentron canadum, Linnaeus). In 2007, methods for capture, transport, acclimation, sampling, conditioned spawning, larval rearing, fingerling production, nursery, shipping and grow-out have been perfected. Survival rates ranging from 17.5% to 35% were achieved from egg to shipping size fingerlings (1.0 g) in 2007 at the University of Miami Experimental Fish Hatchery, with production of approximately 20 000 fingerlings per 12 000 L tank. Wild and F1 broodstock cobia have been conditioned to spawn through temperature manipulation producing viable eggs for experimental and production level larval rearing trials in several hatcheries. Brood fish have also been induced to spawn using hormones. Cobia appear to be susceptible to infestations by parasitic protozoa such as Amyloodinium ocellatum and to infections caused by deleterious bacteria such as Photobacterium spp. and Vibrio spp. Prophylactic methods used to prevent and control epizootic diseases at the hatchery are summarized. Improved techniques for cage management were implemented, and both novel designs of submerged cages deployed in exposed areas and traditional gravity cages in protected areas have been used for commercial ongrowing of cobia in the Americas and the Caribbean region. [ABSTRACT FROM AUTHOR]