Cobia Research Articles

Amidated pleurocidin peptide encapsulated in biodegradable poly(lactide-co-glycolide) microparticles sustains its antibacterial activity against Photobacterium damselae subsp. piscicida in cobia

Photobacterium damselae subsp. piscicida (PDP), the causative agent of fish pasteurellosis, has become a serious threat leading to high mortalities in cage-cultured juveniles of cobia (Rachycentron canadum). However, overuse of conventional antibiotics to control the infection raises the emergence of resistant bacteria as well as the presence of residual drugs in animals and the environment. Further efforts are therefore needed to look for new and effective antibacterial agents, such as antimicrobial peptides (AMPs), for use on the fish farm to replace conventional antibiotics before commercial vaccines against PDP are available. In the present study, the fish-derived AMP, pleurocidin (PLE), was used as an anti-PDP agent. After C-terminal amidation, the resulting amidated PLE peptide, PLE(am), was further encapsulated with the poly (lactide-co-glycolide) (PLG) polymer to generate PLG-PLE(am) microparticles that would sustain release of antibacterial PLE(am) and elicit effective protection against PDP in cobia. PLG-PLE(am) microparticles, 4.25–5.39 μm in diameter, contained 14.69–18.47 μg of entrapped PLE(am) per milligram of dry weight of microparticles and showed 81%~84% entrapment efficiency. The amount of released PLE(am) from PLG microparticles gradually increased over a 28-day triphasic controlled-release period and the released PLE(am) still retained its antibacterial activity. Peritoneal injection with PLG-PLE(am) microparticles further protected all cobia from a lethal peritoneal infection of 2 × 103 CFU PDP (MML-3) and allowed cobia to survive relatively longer (14 days post infection). In conclusion, the sustained release of antibacterial PLE(am) peptide from PLG-PLE(am) microparticles can preserve the antibacterial activity to result in effective protection in cobia. Our study provides notable evidence to indicate the feasibility of using PLG-PLE(am) microparticles as an antibacterial agent against PDP in cobia.

Differential expression of immune-related genes in head kidney and spleen of cobia (Rachycentron canadum) having Streptococcus dysgalactiae infection

Streptococcus dysgalactiae is a gram-positive bacterium and a harmful aquaculture pathogen. To investigate the immune response against S. dysgalactiae, we performed transcriptome analysis of the head kidney and spleen of cobia (Rachycentron canadum) using RNA-seq. Total RNA was extracted from the head kidney and spleen of cobia, 1 and 2 days after treatment with S. dysgalactiae or control PBS. After RNA purification and cDNA library generation, sequencing was performed using the Illumina HiSeq™ 4000 platform. The filtering and de novo assembling transcripts were annotated using several databases. To identify differentially expressed genes (DEGs) between the S. dysgalactiae and PBS groups, the mapped values of fragments per kilobase of transcripts per million fragments were calculated. After de novo assembly, a total of 106,984 transcripts were detected, with an N50 of 3020 bp. These transcripts were annotated and categorised into a total of 7608 genes based on the KEGG pathway database. DEGs (2-fold difference) were calculated by comparing the S. dysgalactiae and PBS control group gene expression levels at each time point. The DEGs were mainly annotated into signal transduction and immune system categories, based on the KEGG database. The DEGs were significantly enriched in the immune-related pathways – “cytokine-cytokine receptor interaction”, “complement and coagulation cascades”, and “hematopoietic cell linage”. In this study, immune-related genes responding to S. dysgalactiae were detected, and several immune system pathways were categorized. We identified the IL17C-related pathway for inducing the expression of pro-inflammatory cytokine genes (IL-1β, IL-6, and IFNγ). Additionally, neutrophil-related genes (CSF3, CD121, and CD114) were induced in the spleen after S. dysgalactiae infection. It was suggested that these pathways contribute to immune responses against S. dysgalactiae infection. The data revealed in this study may offer improved strategies against S. dysgalactiae infection in cobia.

Influences of different arachidonic acid levels and temperature on the growth performance, fatty acid profile, liver morphology and expression of lipid genes in cobia (Rachycentron canadum) juveniles

An 8-week nutritional experiment was conducted with the aim of evaluating the influences of different arachidonic acid (ARA) levels and two different temperatures (29.5 °C and 26.5 °C) on the growth performance, tissue and whole-body fatty acid (FA) compositions, plasma prostaglandin concentration, liver morphology and expression of genes related to lipid metabolism in cobia juveniles. A basal fat-reduced diet was manufactured and subsequently coated with different FA sources, distinct levels of ARA (ARA1, 0.5%; ARA2, 1.2%; and ARA3, 1.9%) and fish oil (FO: 8.8%, as a control diet). All diets were formulated to be isoproteic and isolipidic. Cobia juveniles (5.86 ± 0.40 g) were randomly divided into 24 tanks with 18 animals each. Twelve tanks were kept at 29.5 °C, and 12 tanks were kept at 26.5 °C. The animals were fed twice per day with each experimental diet until apparent satiation in triplicate tanks at both temperatures. The results revealed that the animals maintained at 26.5 °C and fed with the ARA diets exhibited better growth than those fed with the FO diet and kept at 29.5 °C. In contrast to observations in other teleost species, ARA excess did not reduce growth or survival. The FA compositions of the livers, fillets and whole bodies generally reflected the diet compositions, i.e., gradual increases in ARA were observed according to the diet level. Additionally, greater depositions of docosahexaenoic acid (DHA) in the fillets of the animals from the ARA2 group that was kept at 26.5 °C were observed. The plasma prostaglandin levels were greater in the animals that were kept at 29.5 °C for all experimental diets and in the ARA2 animals compared with the FO groups at both temperatures. The FAS and SREBP-1 expressions in the livers were down-regulated in the ARA1 and ARA2 animals that were maintained at 26.5 °C compared with the animals that were fed the same diets but kept at 29.5 °C. Additionally, SREBP-1 expression was up-regulated in the ARA2 animals compared with the FO animals at both temperatures. The results of this study indicated that ARA inclusion between 0.5 and 1.9% combined with a temperature of 26.5 °C can improve juvenile cobia growth performance and directly influence the modulation of prostaglandin synthesis and the relative expressions of lipid genes.

Molecular cloning, characterization and expression analysis of glucose transporters fromRachycentron canadum

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.

Preparation and Identification of Novel Antihypertensive Peptides from the In Vitro Gastrointestinal Digestion of Marine Cobia Skin Hydrolysates.

This research focuses on cobia skin hydrolysates and their antihypertensive effects via the inhibitory activities of angiotensin I-converting enzyme (ACE). Marine fish Cobia (Rachycentron canadum) skin was hydrolysed for 5 h using Protamex and Protease N to obtain the cobia skin protein hydrolysates PX-5 and PN-5, respectively. The soluble protein and peptide contents of the PX-5 were 612 and 270 mg/g, respectively, and for the PN-5, 531 and 400 mg/g, respectively. The IC50 of PX-5 and PN-5 on ACE was 0.221 and 0.291 mg/mL, respectively. Increasing the IC50 from 0.221 to 0.044 mg/mL by simulated gastrointestinal digestion (PX-5G) reduced the ACE-inhibitory capacity of PX-5. Using gel filtration chromatography, the PX-5G was fractioned into eight fractions. The molecular weight of the fifth fraction from PX-5G was between 630 and 450 Da, and the highest inhibitory efficiency ratio on ACE was 1552.4%/mg/mL. We identified four peptide sequences: Trp-Ala-Ala, Ala-Trp-Trp, Ile-Trp-Trp, and Trp-Leu, with IC50 values for ACE of 118.50, 9.40, 0.51, and 26.80 μM, respectively. At a dose of 600 mg PX-5 powder/kg body weight, in spontaneously hypertensive rats PX-5’s antihypertensive effect significantly reduced systolic and diastolic blood pressure by 21.9 and 15.5 mm Hg, respectively, after 4 h of oral gavage.

Common moist diet replacement to promote sustainable Cobia Rachycentron canadum (Linnaeus) near- shore farming in Brazil

ABSTRACT: Cobia is one of the most promising warm water aquaculture species. In Brazil, cobia farming began in 2008 in the state of Rio de Janeiro from experimental scale facilities to regular near-shore farms based on fresh/frozen fish diets composed mostly of Sardinella sp. Despite the encouraging results achieved in the promotion of sustainable cobia farming, we advocate the replacement of fresh/frozen fish by a practical formulated feed. This experiment evaluated the zootechnical performance and environmental efficiency of moist and practical formulated feeds in early grow-out phases in the cycle of cobia nearshore cage culture. Four hundred and twenty juvenile cobia (151 ± 7 g) were fed with moist feed and practical formulated feed for 56 days. Biometrics were taken every two weeks and diets were analyzed for proximate composition, fatty acid composition and pellet quality. Although growth performance was equivalent between treatments, feed consumption and feed conversion ratios (FCR) were different (p < 0.05) and varied according to water temperature. Cobia fed moist feed exhibited an FCR two times higher than those fed formulated feed. Elevated settling speed and low floatability contributed to higher heterogeneity and lower efficiency of fish fed moist diet. Nitrogen excretion rate was reduced (64 %) and protein efficiency ratio elevated (27 %) within formulated diet groups in comparison to those fed moist diet (79 % and 15 %, respectively). The fatty acid profile of cobia muscle was similar across the groups. With no negative effects of diet substitution on production performance and improvement of environmental efficiency, this approach can be applied and advocated globally and contribute to the responsible intensification of sustainable marine fish culture.

EFFECTS OF DIETS WITH DIFFERENT PROTEIN LEVEL FOR COBIA (Rachycentron canadum) GROWTH IN CONTROLLED TANK

The feed given to cobia’s juvennile (Rachycentron canadum) still uses expensive factory-made feed to be the basis of this research. This aims of this research to examine the effect of feed formula with different protein levels on optimal growth cobia. This research method used a completely randomized design (CRD) with three treatments and three replications. The treatment in this study were different protein level commercial feed (as control/46%), and formula feed (protein P1 46% and P2 protein 48%). The parameters tested included absolute weight, daily growth rate, feed conversion ratio, protein retention, and survival rate. The data obtained were analyzed by analysis of variance and continued with the duncan test with a 95% confidence interval. The results showed that the growth of absolute weight and daily growth rates generated from each treatment were significantly different (p &lt;0.05), K (80.30 ± 11.20c g and 1.78 ± 0.25c g/day), P1 (21.87 ± 1.95a g and 0.49 ± 0.05a g/day), P2 (37.43 ± 3.29b g and 0.83 ± 0.07b g/day).

Nutritional regulation of pyruvate kinase and phosphoenolpyruvate carboxykinase at the enzymatic and molecular levels in cobia Rachycentron canadum.

Despite being a carnivorous fish species, cobia (Rachycentron canadum) can utilize high levels of dietary carbohydrate (up to 360gkg-1). By contrast, rainbow trout (also carnivorous) cannot, due to the absence of molecular induction of glycolytic enzyme and inhibition of gluconeogenic enzyme gene expressions such as pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK). We hypothesized that this phenomenon is species-specific and will not be observed in cobia. Our results show that, at the molecular level, the mRNA abundance of the important glycolytic (PK) and gluconeogenic (PEPCK) enzymes in cobia liver are regulated by dietary carbohydrate-to-lipid (CHO:L) ratios and nutritional status (fed, unfed, and refed). Significantly upregulated hepatic PK and depressed PEPCK gene expressions were observed when the fish were fed with an increasing CHO/L-ratio diet or were refed. However, in contrast to gene expression, there was no significant effect of dietary CHO/L ratios on PK enzyme activity. The decrease in PEPCK activity was significantly found between low CHO/L ratio and high CHO/L ratio diets, whereas the moderate CHO/L ratio group showed intermediate values. But PEPCK activity appeared to be independent of nutritional status. These results suggest that nutritional regulation is obvious, at least at the molecular level, in the key hepatic enzymes (PK and PEPCK) of the glucose metabolism pathway, in response to different dietary CHO/L ratios and to the transition from being starved to fed. Determining whether other key enzymes involved in hepatic glucose metabolism contribute to glucose tolerance in cobia is necessary for further investigation of this phenomenon at the enzymatic and molecular levels.

Molecular cloning of IL-6, IL-10, IL-11, IFN-ɤ and modulation of pro- and anti-inflammatory cytokines in cobia (Rachycentron canadum) after Photobacterium damselae subsp. piscicida infection.

Photobacterium damselae subsp. piscicida (P. damselae subsp. piscicida) is the agent of Photobacteriosis, a serious fish disease that produces an acute infection and high mortality in farmed cobia. It has been proved that regulation of pro- and anti-inflammatory cytokines play a central role in initiation of proper inflammatory responses against bacterial infection. Here we have analyzed the expression of pro-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-8 and IFN-ɤ) and anti-inflammatory cytokines (IL-10 and IL-11) in spleen and head kidney during acute P. damselae subsp. piscicida infection of cobia. Our data revealed that cytokines tested showed distinct patterns of expression. While TNF-α and IL-8 showed a decay pattern of expression, IL-1β response was quite late. Moreover, P. damselae subsp. piscicida infection induced the simultaneous expressions of pro-inflammatory (IL-6, IFN-ɤ) and anti-inflammatory (IL-10, IL-11) cytokines. Together these results indicate the innate immunity of cobia is actively suppressed by P. damselae subsp. piscicida.

Effect of increased rearing temperature on digestive function in cobia early juvenile

The present study is focused to elucidate the main characteristics of the digestive function of this carnivorous fast-growing fish living at high temperatures. With this aim, we have examined the effects of an increased temperature from 30 to 34 °C on the daily pattern of gastrointestinal pH, enzymatic proteolytic digestive activity and the feed transit time in early juveniles of cobia (Rachycentron canadum), a species living in tropical and subtropical waters with an increasing aquaculture production. Fish were fed two meals a day. Gastric luminal pH was permanently acidic (mean pH values: 2.76–4.74) while the intestinal pH increased from neutral/slightly acidic to slightly alkaline when the digesta was present, with an increasing alkalinity from proximal to distal intestine (mean pH values: 6.05 to 7.69). The temperature did not affect the gastric pH but a slightly higher acidity was induced in the intestine at 34 °C.Pepsin activity showed a daily rhythm at 30 °C with maximum in the middle of the light period, while at 34 °C some hourly changes coinciding with feed adding without a clear daily trend during the 24-h period were observed. The trypsin activity exhibited a daily rhythm at both temperatures with an increase after morning feeding to reach a maximum several hours later. Average pepsin activity during the daily cycle was slightly higher at 34 °C (6.1 and 7.3 U mg−1 BW at 30 and 34 °C respectively), but values were significantly different only at 8 and 24 h after the morning meal. Similarly, the trypsin activity was significantly affected by the temperature only at 8 and 16 h after the morning meal, but daily activity averages were similar (1.20 and 1.29 U g−1 BW at 30 and 34 °C respectively).The partial transit rates of the first meal in the stomach for each period inter-samplings were higher during the first 4-h period and decreased progressively along the rest of the 24-h cycle at both temperatures, but no significant differences were detected at 30 °C. In addition, the transit was notably faster at 34 °C particularly during the first 8 h after feeding, with rates between 100 and 65% of total volume displaced (intake or released) during each 4-h period. In the intestine the transit rate was relatively constant and similar at both temperatures during 12 h after feeding. Then the rates remained very low during the following 12 h.Residence time of the first meal was longer at 30 than at 34 °C, particularly in the stomach (12 h:02 min vs 4 h:54 min respectively). In the intestine the difference was not so large (8 h:18 min vs 6 h:24 min respectively). In a parallel study under same conditions, cobia reared at 30 °C grew faster and showed a more favorable feed conversion ratio than those at elevated temperature (34 °C). The present results indicate that at 34 °C, a subtle increase of proteolytic activity cannot compensate for the faster gut transit rate. Therefore, 30 °C is more appropriate temperature for the early on-growing of cobia because at higher temperatures the digestion efficiency decrease being one of the causes for a lower growth.

HÁBITO ALIMENTAR DO BEIJUPIRÁ EM PERNAMBUCO, NORDESTE DO BRASIL

O hábito alimentar do beijupirá, Rachycentron canadum, foi descrito ao longo da costa do Estado de Pernambuco, Nordeste do Brasil. Foram capturados 110 exemplares entre fevereiro/2004 e agosto/2006, com comprimento furcal ou zoológico variando entre 40,0 e 137,0 cm (média e desvio padrão: 85,8±18,0 cm) e peso total entre 0,4 e 29,8 kg (7,5±4,4 kg). Foi avaliada a importí­¢ncia de cada item alimentar na dieta utilizando o í­­ndice de importí­¢ncia relativa (IIR). Dentre os 110 estômagos analisados (52 fêmeas e 58 machos), 92 (83,6%) com algum item alimentar e 18 (16,4%) vazios. Os peixes ósseos foram os principais itens consumidos na dieta alimentar (IIR = 98,7%), entre os quais a mariquita (Holocentrus adscensionis) e o baiacu (Diodon sp.) foram as presas mais consumidas (IIR = 30,7% e 8,2%, respectivamente). A dieta foi composta, ainda, por elasmobrí­¢nquios, crustáceos e cefalópodes (IIR &lt;1% cada). Não foram encontradas diferenças na dieta entre os sexos e classes de tamanho (&lt; ou â"°¥ 69,8 cm de comprimento furcal, L50 estimado para a espécie). Os dados analisados demonstram que, na costa de Pernambuco, o beijupirá é um predador carní­­voro com preferência por peixes ósseos demersais, independente do tamanho e sexo dos indiví­­duos analisados.

Feeding of juvenile cobia, Rachycentron canadum: Evaluation of practical feeds, comparison of commercial fishmeal replacers, and estimation of essential amino acid requirements

Three studies were conducted with juvenile cobia, Rachycentron canadum: (Study 1) a 10‐week feeding trial within floating net cages to test the nutritional efficacy of different dietary feeding regimes (trash‐fish control diet, a semimoist diet, an in‐house dry formulated diet, and a commercial cobia feed); (Study 2) a 10‐week feeding trial within an indoor water‐recirculating tank‐based system to test the nutritional efficiency of different potential dietary fishmeal replacers (poultry byproduct meal, soy protein concentrate, feather meal), a diet without taurine supplementation, and a commercial cobia feed; and (Study 3) estimation of the essential amino acid (EAA) requirements of cobia based on EAA whole‐body composition in fast‐growing cobia fed a trash‐fish‐based diet. Fish performance in terms of growth and feed efficiency was the greatest within the outdoor net‐cage feeding trial, with fish fed the control trash‐fish‐based diet exhibiting the best performance. Although fish growth was poorer within the indoor feeding trials, fish performance was similar for most diets, with apparent crude protein digestibility coefficients of over 75% being obtained in all experimental diets in both feeding trials. The estimated EAA requirements of cobia obtained during this study were similar to those reported for other similar marine carnivorous fish species.

Physical, chemical and sensory evaluation of meat from cobia (rachycentron canadum), desensitized with different voltages of electric shock, stored under refrigeration

ABSTRACT: Fish quality is conditioned by several factors, among them desensitization methods applied for fish managing and slaughtering. This research used electric shock at different intensities as a desensitization method for cobia (Rachycentron canadum) slaughtering and evaluated its effects over fish quality during refrigerated storage. The experiment was carried out by numbing the fish with electroshock at the intensities of 100, 150 and 200 Volts, and keeping them in refrigerated storage for 21 days. On the cobia, obtained from a commercial fish farm the following physical, chemical and sensorial characteristics as quality variables were evaluated: dielectric properties, rigor index, pH, texture, color, sensorial evaluation of freshness, ATP and degradation catabolites. The experimental design was a 6×3 factorial (6 times of analysis and 3 electroshock intensities). Significant differences (P&lt;0.05) were observed for the analyzed variables, as a consequence of desensitization treatments and of storage time within each treatment. However, the number of variables affected by the treatment was smaller than the number of variables significantly affected by the storage time, and the interaction time×treatment was highly significant within the results reported. The best results for the parameters tested were obtained when the treatment at 150 volts intensity with the majority of analyzed variables held significant differences (P&lt;0.05) among treatments. It was also concluded that cobia can be conserved in refrigerated storage within seven days after slaughtering using electro-narcosis as a method of desensitization.

The ecological and economic potential for offshore mariculture in the Caribbean

Offshore mariculture could enable increased seafood production and economic development while alleviating pressure on coastal ecosystems and wild fisheries. In the Caribbean, however, an integrated assessment of the ecological and economic potential for mariculture in the region is lacking. We assess site suitability and develop a spatial bioeconomic model to predict yields and profits for offshore cobia (Rachycentron canadum) mariculture across 30 jurisdictions in the Caribbean. We find that (1) approximately 1.4% of the study area may be technically feasible; (2) the model could avoid conflicts with other uses and sensitive habitats and protected areas; and (3) the model could be economically profitable, with the potential to produce almost half the amount of seafood that is currently harvested from wild fisheries globally. Here, we show that potential farm-scale production and profitability vary across and within countries and that accounting for the foreign investment risk associated with a country will impact estimated farm profitability. Offshore mariculture could promote food security and economic development while sparing wild fisheries. This model-based study finds that the Caribbean could produce over 40 million metric tons of cobia (Rachycentron canadum), about half as much as the current global wild fish catch, and in less than 1.5% of the study area.

Molecular characterization and expression analysis of the CCR9 gene from cobia (Rachycentron canadum) following bacterial and poly I:C challenge

ABSTRACT Chemokine receptors play an important role in coordination of cell trafficking in many biological processes. In this study, a CC chemokine receptor 9 of cobia Rachycentron canadum (RcCCR9) was identified. Analysis of the ORF (1119 bp) of RcCCR9 revealed a predicted protein of 41.87 kDa with typical seven transmembrane domain architecture. RcCCR9 shared several conserved structural features with homologs from mammals and other fish, and had a consistent relationship with phylogenetic trees and sequence identities. Reverse transcription quantitative PCR analysis showed ubiquitous RcCCR9 transcripts in healthy cobia, mainly in immune-related organs, with the highest levels in blood and lower levels in intestines and brain. After challenge with inactivated Vibrio harveyi or viral mimic poly I:C, RcCCR9 expression was up-regulated in head kidney and down-regulated in spleen. Compared with poly I:C, V. harveyi induced a stronger up/down-regulation of CCR9 mRNA levels in the central immune organs. RcCCR9 seems to be strongly involved in host defense against bacterial infection.

Performance of cobia grown in brackish water and fed with different feeding rates

Abstract: The objective of this work was to evaluate different feeding rates on the productive performance of cobia (Rachycentron canadum) grown in brackish waters. For the experiment, 1,600 juveniles were distributed in 16 enclosures installed in an estuarine pond. Four different feeding rates were evaluated: 1, 3, 5, and 7% live weight (LW) per day. The following performance parameters were assessed: survival, final biomass, specific growth rate, daily weight gain, apparent feed conversion, protein efficiency rate, lipid efficiency rate, and hepatosomatic index. Survival was greater than 80% at all feeding rates. The most efficient feed conversion rate was obtained with the feeding rate of 5% LW per day, which also resulted in better values for the hepatosomatic index. The rate of 5% LW per day provides a better productive performance for cobia in brackish waters.

Withdrawal Period of Oxolinic Acid in Cobia (Rachycentron canadum): Validation of an LC-MS/MS Method

Oxolinic acid (OXO) has been routinely used in aquaculture as both prophylactic and chemotherapeutic agents, principally against systemic bacterial infections. The residue depletion of OXO was investigated in cobia following multiple (5 days) in-feed dosing (30 and 60 mg/kg body weight/day) at 25°C; we assessed OXO concentrations of liver and muscle (+skin) samples post-treatment for three weeks. The OXO residues were quantified using a validated ultra-high-performance liquid chromatographytandem mass spectrometry (UPLC-MS/MS) method and the results indicated recoveries of 86.6-95.8%, with relative standard deviations (RSD) less than 8.5% for intra- and inter-day precisions. Within the range of 10−500 ng/g, the calibration curves for all matrices presented a determination coefficient greater than 0.99. Limit of detection and quantification were estimated at 6 and 10 ng/g, respectively. In order to account for the high variability of the residue data, a safety span corresponding to 50% of depletion time could be seen as appropriate. Considering a maximum residue limit (MRL) of 50 ng/g established by the Taiwan FDA for OXO in muscle with skin in natural proportions, a withdrawal period of 15 days was calculated for the sum of 10day depletion time and 5-day safety span. These results revealed that the analytical method is developed for residue OXO and that the withdrawal period is appropriate.

Voluntary feed intake and transition of ingesta in the gastrointestinal tract of juvenile cobia (&lt;i&gt;Rachycentron canadum&lt;/i&gt;) feed different diets

This study aimed to evaluate the palatability of a plant based protein diet (BL/A), with high inclusion levels of plant protein sources but balanced in lysine to arginine ratio (1.1), compared to two locally commercial pellets CD1 (Uni-President, Ltd.) and CD2 (INVE, Ltd.), and the transition of ingesta in juvenile cobia. Juvenile cobia were fed to satiety with each of the three diets had equal feeding rate of 5.3-5.4±0.3% BW (for a meal). No differences in stomach filling occurred between cobia fed the PBD diet and those fish fed the CD1 or CD2 diet. Gastric evacuation rates in cobia were performed as an exponential relationship, and were estimated as the function VT=V0 e-b(x) (VT, volume of feed at time T; V0, volume of feed at time 0; b, the instantaneous evacuation rate; and x, time postfeeding; R²&gt;0.95). Between 77 to 80% of the stomach contents were evacuated to the lower parts of the gastrointestinal tract at 8 h, and most of consumed feed (98%) was emptied out of the stomach at 16 h postfeeding. This was supported by the fact that cobia had good appetite in the 2nd feeding of the day. Time required for the return of appetite in cobia was within 8 h after feeding to satiation.&#x0D; Key words: Cobia, lysine, arginine, evacuation

Seguimiento y simulación de las actividades y la generación de residuos disueltos del cultivo piscícola de la especie cobia en la costa de Cartagena, Colombia

En 2008 se construyó la primer granja piscícola en Colombia en la isla de Tierrabomba cerca de Cartagena de Indias (10.3601 – 75.5966 NW). En el cultivo se sembró cobia (Rachycentron canadum). Esta especie crece muy rápidamente, tiene un alto valor en el mercado, y ha sido cultivada exitosamente en el Caribe. Tres años después de iniciar el cultivo, comenzó un estudio para determinar el impacto del cultivo sobre el ambiente circundante. Mensualmente, durante ocho meses se midieron las variables físicas y los nutrientes en la columna de agua en tres estaciones localizadas cerca de las jaulas (5, 30, 100 m) y un punto control (1000 m). En cada estación se colectaron muestras a las profundidades de 7, 15 y 30 m. Adicionalmente, se instaló un perfilador de corrientes Doppler cerca al cultivo y se colectaron los datos continuamente. Esta información fue ingresada y analizada con el Programa de Simulación para Cultivos Marinos AquaModel (www.aquamodel.org). Este programa comprende un sistema de submodelos para la fisiología del pez, la hidrodinámica, la calidad del agua, la dispersión de desechos disueltos y particulados, producidos por el cultivo, y las transformaciones ecológicas de estos desechos en la columna de agua. La simulación 4-D del AquaModel de la operación de la granja y el impacto ambiental es conducido por las corrientes que mide el perfilador Doppler así como por las mediciones en campo como son la temperatura del agua, y las concentraciones de oxígeno, nutrientes y clorofila a. Las tasas de crecimiento simuladas para el pez concordaron con los cambios temporales en el tamaño de los peces colectados en el campo. La simulación también indicó que el impacto ambiental del cultivo no fue significativo. Tanto las mediciones en campo como la simulación muestran que hay una rápida dilución del nitrógeno total disuelto en el gradiente horizontal, y que la concentración de oxígeno en las

The role of dietary methionine concentrations on growth, metabolism and N-retention in cobia (Rachycentron canadum) at elevated water temperatures.

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.