Temperature dependent pre- and postprandial activity in Pacific bluefin tuna (Thunnus orientalis)

The fasted and post-prandial physiological responses of the Patagonian blennie Eleginops maclovinus

Eleginops maclovinus is a native species with potential for Chilean aquaculture. Understanding the variations between the post-prandial and fasted metabolic responses can contribute to improving the aquaculture of this species. This study aimed to characterize variations in intermediate metabolism during the course of the day in the liver, serum, and gills of fed and unfed fish. For this, 72 fish were assigned to two experimental groups, "fed" and "fasted". The first group was fed "ad libitum" at 8.30, while the fasted group was not fed for 24 h. Samples were taken from both groups at 9:00, and every 2 h: 11:00, 13:00, 15:00, 17:00, and 19:00. In the fed group, food spent a long time in the gastrointestinal tract, with a large increase in stomach size and without evidence of complete emptying of the stomach at 19:00 (10.5 h post-feeding). In serum, the levels of amino acids, glucose, and triglycerides presented significant differences with peak levels at different times of day in the fed group. The cortisol in the fasted group presented a diurnal pattern with high levels during the morning and very low levels after 13:00, while in the fed group, the high cortisol variability did not allow a clear pattern to be established. In the liver, the effect of time on the enzymatic activity of the intermediary metabolism was greater compared to the effect of feeding. In the liver, enzyme activity decreased at later hours of the day, while glycogen levels increased at later hours of the day in both groups: but its levels were higher in the fed group. In gills, as well as in the liver, time had a greater effect than feeding on intermediate metabolism, since feeding only had a significant effect on the levels of hexokinase, lactate, and amino acids, suggesting an effect on carbohydrate metabolism. Meanwhile, time significantly affected the levels of Na⁺, K⁺-ATPase, glutamate dehydrogenase, aspartate aminotransferase, amino acids, and proteins, suggesting an effect on amino acid metabolism. In conclusion, the intermediate metabolism of E. maclovinus presents variations according to the time of day, with an increased metabolism during the morning and decreased metabolism as the day progresses, especially at the hepatic level. The gill tissue, despite not being a metabolic organ, presents feeding-dependent variations in its metabolism. Additional studies will be required to corroborate if coordinating a feeding strategy during the first hours of the day when metabolism is greater would improve the growth of E. maclovinus.

Environmental changes affecting physiological responses and growth of hybrid grouper - The interactive impact of low pH and temperature

Rising of temperature in conjunction with acidification due to the anthropogenic climates has tremendously affected all aquatic life. Small changes in the surrounding environment could lead to physiological constraint in the individual. Therefore, this study was designed to investigate the effects of warm water temperature (32 °C) and low pH (pH 6) on physiological responses and growth of hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) juveniles for 25 days. Growth performance was significantly affected under warm water temperature and low-pH conditions. Surprisingly, the positive effect on growth was observed under the interactive effects of warm water and low pH exposure. Hybrid grouper exposed to the interactive stressor of warm temperature and low pH exhibited higher living cost, where HSI content was greatly depleted to about 2.3-folds than in normal circumstances. Overall, challenge to warm temperature and low pH induced protein mobilization as an energy source followed by glycogen and lipid to support basal metabolic needs.