Search

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.

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 °

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.

Water temperature is a key factor affecting metabolic rates and therefore fish feeding physiology and behavior. These effects have a special significance in the scenario of the global warming. In this study we have examined effects of an increased water temperature on the daily pattern of gastrointestinal pH, enzymatic proteolytic digestive activity and the food transit time in early juveniles of cobia (Rachycentron canadum), a candidate species for aquaculture in tropical and subtropical waters. Juveniles (3.7±0.4 g wet BW) were randomly distributed to 6 experimental 200-L tanks (60 fish tank-1) and reared at two temperatures (30 and 34 °C) in recirculation systems for six weeks. Fish were fed twice a day (8:00 and 16:00h) with an experimental diet containing 47% protein and 10% lipid. At the end of the experiment, fish were sampled every 4 hours to obtain daily patterns of processes related to digestive activity. Cobia reared at 30oC grew faster and with higher FCR than those at elevated temperature (34oC). The fish reared at high temperature had lower intestinal luminal pH but similar gastric pH. Overall the pepsin activity during the complete daily cycle, but it was significantly different from the fish maintained at 30oC only at 8 hours post-feeding. Similarly, the trypsin activity was not significantly affected by the water temperature but tended to be higher at 34°C during the first hours postfeeding. The transit rate was notably faster 34°C in the stomach but similar in the intestine. These results indicate that the slight increase of proteolytic activity that was observed at 34°C cannot compensate for the faster gut transit rate. The reduced time the dietary proteins are available for hydrolysis can explain the lower growth observed at this temperature.

Efficient macronutrients digestion depends on the time the feed is available for hydrolysis within the different sections of the digestive tract under the appropriate digestive enzymes. In fish, feed transit rates usually are estimated from gut filling or evacuation after a unique meal. Nevertheless, food residence time within the gut is dependent on the feeding frequency, as well as on the environmental conditions. In this study we have analyzed the transit rate in the stomach and intestine in early juveniles of cobia (Rachycentron canadum) under routine feeding and at two different temperatures. Juveniles (3.7±0.4 g wet BW) were randomly distributed to 6 experimental 200-L tanks (60 fish tank-1) and reared at two temperatures (30 and 34 °C) in recirculation systems for six weeks. Fish were fed twice a day (8:00 and 16:00 h) with a diet containing 47% protein and 10% lipid. The diet included yttrium (Y) as marker only in the morning meal. At the end of the experiment, fish were sampled every 4 hours and Y-content in the stomach and intestine was analyzed by ICP-mass spectrometry. Total gut content at each sampling time was estimated from the weight of the stomach and intestine, and the transit rate from the difference of Y content between successive sampling. In juvenile cobia, mass and volume of the stomach are much higher than in the rest of the intestine. The feed transit rate in the stomach was notably faster at 34 than at 30 °C during the first eight hours post-feeding; afterwards the rate was similar at both temperatures. Contrarily, no differences were found in the intestine, but transit rate declined drastically to residual values 12 h post-feeding. The increased temperature induced a change of filling pattern and a decrease of food residence time in the stomach.

Increased sea temperature due to climate change will affect the physiology, behavior, and geographical distribution of marine species, including fish (Botkin et al., 2007). However, little information is available on the impact of elevated temperature and interactions with appetite, amino acid metabolism and growth in cobia (Rachycentron canadum), a candidate species in aquaculture. This work is part of a larger study aimed to determine whether there is a link and possibly a positive effect between the dietary methionine levels, elevated temperature and feed intake. Here we describe the effects on appetite and mRNA expression of the orexigenic (appetite stimulant) neuropeptide Y (NPY), agouti-related protein (AgRP), and the anorexigenic (appetite inhibiting) cocaine- and amphetamine-regulated transcript (CART) and cholecystokinin (CCK) in cobia brain.

This study examines the postprandial pH changes in the digestive tract of Cobia juveniles reared at 30° and 34° C. Cobia juveniles maintain a gastric luminal pH close to 4 throughout the day. A slight increase occurred after feeding due to the buffering and dilution effect of the ingested food and drinked sea water. In the intestine the luminal pH increased after the first meal and declines to neutral values by the end of the day. Higher alkalinization was observed in the intestine at 34° than at 30° C.

Increased sea temperature due to global warming will affect the physiology, behavior, and geographical distribution of marine fish (Botkin et al., 2007). Temperature is one of the vital factors affecting metabolism, growth and energy budget of fish, as for other ectothermic organisms (Hunter et al., 2016). Until now, there is no information available on the impact of temperature on amino acids metabolism on cobia (Rachycentron canadum), a candidate species in aquaculture. The present study aimed to determine the interactions of elevated temperature and dietary methionine on growth, metabolism and N-retention in cobia.