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This study aimed to determine the impact of elevated temperature combined with different levels of dietary methionine concentrations on feed intake (FI) and brain expression of selected neuropeptides and one receptor involved in appetite control in juvenile cobia (approximately 3.7 g body weight). The genes studies were neuropeptide y, npy; agouti-related protein, agrp; cocaine- and amphetamine-regulated transcript, cart; cholecystokinin, cck and melanocortin 4 receptor; mc4r. The cobia were reared at typical sea water temperature in Vietnam (30 °C) and elevated temperature (34°C; selected as one of the predicted scenarios of climate change). The fish were fed diets with different levels of methionine: deficient (M9; 9.1 g/kg), sufficient (M12; 12.8 g/kg) and surplus (M16, 16.8 g/kg) for 6 weeks (triplicate tanks per treatment). Both dietary methionine concentration and temperature affected FI in cobia. Dietary methionine deficiency (i.e., M9) and elevated temperature reduced FI in cobia. Temperature significantly influenced the mRNA expression of agrp, cart, cck and mc4r. Expression of the orexigenic neuropeptide npy was consistently higher before the meal than after the meal for all diets and at both temperatures. At 30°C, prefeeding levels of npy correlated with both increased methionine levels and FI. The interaction between dietary methionine and temperature on the levels of brain npy expression was significant (P<0.05). There was higher brain expression of agrp, cart and cck in cobia at 34°C than in fish at 30°C, which was correlated with a lower FI. In conclusion, both feeding, temperature and/or dietary methionine levels affected the brain expression of npy and agrp, cart, cck and mc4r. This suggests that these neuropeptides as well as the mc4r receptor are actively involved in adjusting feed intake to compensate for changing energetic demands, as well as metabolic adjustments due to the variable availability of methionine at elevated temperature.

This study aims to explore the impact of dietary methionine concentrations combined with temperatures on feed intake (FI) and expressions of appetite neuropeptides (neuropeptide y, npy; agouti-related protein, agrp; cocaine- and amphetamine-regulated transcript, cart; and cholecystokinin, cck) and one receptor (melanocortin 4 receptor mc4r) in the brain of cobia. The juvenile cobia (ca 3.7g body weight) were reared in two recirculation systems at control temperature (30°C) and elevated temperature (34°C) at the Center for Aquatic Animal Health and Breeding Studies (Nha Trang University, Vietnam). The fish were fed diets with different levels of methionine; deficient (M9; 9 g/kg), sufficient (M12; 12 g/kg) and surplus (M16, 16 g/kg) for 6 weeks (triplicate tanks per treatment). Results showed that cobia fed M9 diet had a lower FI at both temperatures. Further, there was a significant interaction between dietary methionine levels and temperature on FI, with a lower FI in cobia at 34°C compared to fish kept at 30°C and fed the M12 diet and M16 diets. Feed intake was correlated to brain mRNA expression levels of npy and agrp, while temperature significantly influenced the mRNA expression of agrp, cart, cck and mc4r. Expression of the orexigenic neuropeptide npy were consistently higher before the meal compared to after the meal for all diets and at both temperatures. At 30°C pre-feeding levels of npy correlated with both increased methionine levels as well as FI. The interaction between dietary methionine and temperature on levels of brain npy expression was significant (P<0.05). There was a higher brain expression of agrp, cart and cck in cobia at 34 °C compared to fish at 30 °C that was correlated with a lower FI. In summary, both feeding, temperature and/or dietary methionine levels affected the brain expression of npy and agrp, cart and cck suggesting that these neuropeptides are actively involved in adjusting feed intake to compensate towards changing energetic dem

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.

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.

Investigation of some aspects of biology of a recreationally and commercially important fish, cobia, Rachycentron canadum in Dungun coast, Malaysia was conducted between April 2014 and May 2015. A total of 249 specimens were opportunistically collected from the catches of trawl net, gill net and by hooks and line. The total length ranged from 39.20 to 143.00 cm (88.29 ± 1.28 cm), fork length ranged from 37.50 to 124.00 cm (78.69 ± 1.09 cm) while the wet weight ranged from 0.50 to 20.40 kg (5.51 ± 0.26 kg). There was no significant difference in all the morphometric characters between sexes except for head width (HW) (p < 0.05). Ten (10) out of the seventeen (17) truss distances in the body landmarks of cobia showed significant differences between males and females. The equation of length-weight (LW) relationship for combined sex was W = 0.000002FL3.3204 (R² = 0.92). The growth of cobia in Dungun water followed positive allometric as the growth coefficient (b) was higher than 3. Observed length frequency of both sex followed a normal distribution pattern and there was a predominance of cobia in the medium size range from 65 - 85 cm fork length for the females and 55 - 90 cm for the males. The sex ratio of females to males was 1:1.18 and it was not significantly different from the expected 1:1 (X2 = 2.12 df = 1; p < 0.05). Growth parameters of von Bertalanffy growth formula for cobia estimated were L = 142.00 cm, K = 1.20 yr-1, while natural mortality rates (M), fishing mortality rate (F), total mortality (Z) and Exploitation rate (E) estimated were 1.34, 0.95, 2.29 and 0.41 respectively. The maximum allowable limit of exploitation (Emax) was estimated to be 0.56. The sizes attained by cobia at the end of age 1 (year) was 99.28 cm. The estimation of fork length at first maturity (Lmat) from the plot of gonadosomatic index (GSI) against fork length (FL) indicated early maturation of males compared to females with respective value of 70 cm and 72 cm. Males with mature g

Worldwide, the growth of marine aquaculture is limited by a number of factors. One of the most important is the development of larviculture protocols to produce adequate numbers of juveniles to stock grow-out systems at a convenient cost. In order to develop a tool to assess the nutritional status of cobia larvae, we have cloned and sequenced the Growth Hormone (GH) from the pituitary gland of adult fish, and examined the ontogenetic expression in embryonic and larval specimens by qPCR, as well as tissue distribution in wild adult animals by RT-PCR. The cobia GH sequence showed similarity to the GH sequence of Coryphaena hippurus (mahi mahi), Seriola dumerili (Greater amberjack) and Seriola quinqueradiata (Yellowtail). GH gene expression was studied in 18 different tissues, but was only detected in the pituitary gland, eyes, gill and red muscle. Expression levels were very low in embryos and in early larvae but just before the first feeding, gene expression increased dramatically (~1000 fold) and remained high for the rest of the collection period (to 300 h post fertilization). This pattern of expression is similar to that seen in other rapidly growing temperate marine fish and underscores the rapid somatic growth that begins with the onset of feeding in cobia., A nivel mundial, el crecimiento de la acuicultura marina está limitado por una serie de factores. Uno de los más importantes es el desarrollo de protocolos de larvicultura para producir un número adecuado de juveniles para abastecer los sistemas de engorda a un costo conveniente. Con el fin de desarrollar una herramienta para evaluar el estado nutricional de las larvas de cobia, se ha clonado y secuenciado la Hormona de Crecimiento (GH) de la hipófisis de peces adultos, y se examinó la expresión ontogenética en muestras de embriones y larvas por qPCR, así como la distribución en los tejidos en animales adultos silvestres mediante RT-PCR. La secuencia de GH de cobia mostró similitud con la secuencia de GH de Coryphaena hippurus (mahi mahi), Seriola dumerili (mayor medregal) y Seriola quinqueradiata (jurel). La expresión del gen GH se estudió en 18 tejidos diferentes, pero sólo se detectó en la hipófisis, los ojos, branquias y músculo rojo. Los niveles de expresión fueron bajos en los embriones y larvas, pero justo antes de la primera alimentación, la expresión de genes se incrementó dramáticamente (~ 1000 veces) y se mantuvieron altos durante el resto del período de recolección de muestras (300 h después de la fecundación). Este patrón de expresión es similar al observado en otras especies de peces marinos de aguas templadas con rápido crecimiento y se remarca con un rápido crecimiento somático que inicia con la primera alimentación en cobia.

Investigation of some aspects of biology of a recreationally and commercially important fish, cobia, Rachycentron canadum in Dungun coast, Malaysia was conducted between April 2014 and May 2015. A total of 249 specimens were opportunistically collected from the catches of trawl net, gill net and by hooks and line. The total length ranged from 39.20 to 143.00 cm (88.29 ± 1.28 cm), fork length ranged from 37.50 to 124.00 cm (78.69 ± 1.09 cm) while the wet weight ranged from 0.50 to 20.40 kg (5.51 ± 0.26 kg). There was no significant difference in all the morphometric characters between sexes except for head width (HW) (p < 0.05). Ten (10) out of the seventeen (17) truss distances in the body landmarks of cobia showed significant differences between males and females. The equation of length-weight (LW) relationship for combined sex was W = 0.000002FL3.3204 (R² = 0.92). The growth of cobia in Dungun water followed positive allometric as the growth coefficient (b) was higher than 3. Observed length frequency of both sex followed a normal distribution pattern and there was a predominance of cobia in the medium size range from 65 - 85 cm fork length for the females and 55 - 90 cm for the males. The sex ratio of females to males was 1:1.18 and it was not significantly different from the expected 1:1 (X2 = 2.12 df = 1; p < 0.05). Growth parameters of von Bertalanffy growth formula for cobia estimated were L = 142.00 cm, K = 1.20 yr-1, while natural mortality rates (M), fishing mortality rate (F), total mortality (Z) and Exploitation rate (E) estimated were 1.34, 0.95, 2.29 and 0.41 respectively. The maximum allowable limit of exploitation (Emax) was estimated to be 0.56. The sizes attained by cobia at the end of age 1 (year) was 99.28 cm. The estimation of fork length at first maturity (Lmat) from the plot of gonadosomatic index (GSI) against fork length (FL) indicated early maturation of males compared to females with respective value of 70 cm and 72 cm. Males with mature g

During preliminary research on cobia (Rachycentron canadum, L.) it became increasingly clear that more in-depth information was required to provide enabling techniques for the cobia aquaculture industry to develop more rapidly. A unifying theme in many of the more important issues facing cobia aquaculture is nutrition. This led to nutritional investigations with larval and juvenile fish highlighting the impacts of dietary ingredients on animal performance. Indeed, nutrition can be viewed as a central lever of action through which many aspects of the physiology and the environmental (water) quality of the animal can be controlled. The first project focused on studying the larval development of cobia, a fish species highly suitable for aquaculture for which the industry is nascent. I described the time-course of development of external sensory organs, gut morphology and relevant digestive enzymes under controlled conditions using electron microscopy, histology and spectrophotometric assays. The developmental sequence of larval cobia could be separated in two phases, with a transition period between 12 and 14 days post hatch (dph). This transition is characterized by the formation of the intestinal loop, the establishment of basic cranial neuromast configuration, leading to the initiation of the onset of pancreatic enzymes and the increase of growth rate. In addition, the effects of dietary taurine supplementation and incorporation of mannan oligosaccharides (MOS) into live feeds on cobia larvae development was examined. Fish fed supplementary MOS did not grow faster but displayed higher microvilli length and density. In addition, MOS-fed fish were more resistant to salinity stress. The dietary supplementation of taurine resulted in a dramatic increase in survival, growth and development rates, and enzymatic activities. The second project aimed at refining cobia juvenile nutrition, assessing fish meal and fish oil replacements. Novel sources, including soy protein and

Cobia (Rachycentron canadum) is a tropical marine fish, with increasing commercial aquaculture importance worldwide. One of the major limitations to intensive aquaculture is disease. Diseases spread rapidly in an aquatic environment and pose a major threat to the development and introduction of new species, such as cobia, in aquaculture. This is due to the necessity to use wild caught broodstock, which pose a greater threat to introducing disease to a facility. Bacteria of the genus Vibrio play a major role in the diseases of cultured cobia and other species of marine fish. The goal of this study is to reduce the incidence of disease in a population, by either eliminating the potential pathogen or increasing the resistance of the host. To reach that goal, a disinfection assay to evaluate the effectiveness of nine common aquaculture chemical disinfecting compounds was evaluated against two bacterial pathogens (Vibrio anguillarum and V. ordalii). Both bacterial species were susceptible to a variety of common disinfecting compounds including Chloramine-T®, chlorine, ethanol, iodine, Lysol®, Roccal®-D Plus, and Virkon-S®. In addition, both species showed a resistance to disinfection with formalin and tap water. The humoral immune response of cobia to vaccination with a commercially-available vaccine for Vibrio spp. was evaluated by an ELISA. There was a significant difference between control and vaccinated groups (P<0.0001), showing significant antibody production resulting from vaccination.

Cobia represents one of the most attractive candidate species for aquaculture in the history of the industry. With rapid growth rate, high survival rates, and delectable flesh, cobia possess highly desirable characteristics for a cultured fish. Although interest in this species is high, issues pertaining to nutritional requirements must be resolved if this animal is to be produced sustainably. Cobia are high level marine carnivores and, as such, require relatively high dietary protein levels which usually are met through the use of fish meal. Fish meal supplies have become limited and costly, and alternate proteins must be utilized if future aquaculture production is to meet demand. Moreover, the movement towards organic aquaculture production presents additional challenges with respect to fish meal inclusion in aquafeeds designed for cobia. This thesis summarizes research pertaining to fish meal replacement in cobia aquafeeds with organically certifiable alternate protein sources. Initial trials with an organically certifiable yeast-based protein source indicated that up to 25% of the fish meal could be replaced without detrimental impacts to growth rates, feed efficiency, or biological indices. Substitution levels above this resulted in decreased performance in all measured parameters. Based on these results and other research however, it is hypothesized that fish meal replacement levels could be increased to 40% without detrimental impacts upon production characteristics. In a subsequent study, multiple organically certifiable alternate protein sources were investigated for their ability to replace fish meal in aquafeeds for juvenile cobia. A 25% inclusion level of yeast-based protein was used along with a 40% inclusion level. The remaining alternate proteins (soybean meal, soybean isolate, and hemp) also were included at 40% of dietary protein. Two additional diets were formulated to contain all four alternate proteins with or without 8% fish meal. Lack of fish