Influence of photoperiod and protocol length on metabolic rate traits in ballan wrasse Labrus bergylta

Metabolic Rate of Goldfish (Carassius auratus) in the Face of Common Aquaculture Challenges

This study examined the metabolic rate (MO2, oxygen consumption) of goldfish (Carassius auratus) under normal management conditions in aquaculture. Using an intermittent respirometry system, we assessed daily variations and the effects of feeding, handling, temperature increase, and anesthetics. MO2 exhibited a daily rhythm, with higher values during day. Feeding to satiety produced a 35% increase in MO2 compared to fasted animals, with a maximum peak after 3 h and returning to baseline after 7 h. Handling stress (5 min) produced a 140% MO2 peak (from 180 to 252 mg O2 kg-1 h-1), returning to the routine MO2 after 2.5 h. An increase in water temperature (+0.1 °C min-1) up to 30 °C caused MO2 to peak at 200% after 2.5 h from the start of the temperature increase. The use of common anesthetics in aquaculture (MS-222, 2-phenoxyethanol and clove oil in deep anesthesia concentration) affects MO2 during the first few minutes after anesthetic recovery, but also during the following 4 h. It can be concluded that the metabolic rate is a good indicator of the goldfish's response to aquaculture practices involving energy expenditure and stress. Thus, intermittent respirometry is a valuable non-invasive tool for understanding and improving fish welfare in aquaculture.

The crosstalk between photoperiod and early mild stress on juvenile oscar (Astronotus ocellatus) after acute stress

Early mild stress (EMS) is like preparedness and might help fish deal with stress appropriately. This study investigated how EMS and photoperiod changes can impact growth, haematology, blood biochemistry, immunological response, antioxidant system, liver enzymes, and stress response of oscar (Astronotus ocellatus; 7.29 ± 0.96 g) before and after acute confinement stress (AC stress). Ten experimental treatments included five different photoperiods 8L16D (08:16 light to dark), 12L12D (12:12 light to dark), 16L8D (16:08 light to dark), 20L4D (20:04 light to dark), and 24L0D (24:00 light to dark), and these five photoperiod schedules were conducted in an EMS condition. After 9 weeks, no significant differences were found in growth parameters, survival rate, and body composition. At the end of the experiment and after AC stress, fish farmed in 24 light hours had the lowest haematocrit, white blood cells, total protein, blood performance, lysozyme, immunoglobulin M, complement C3, superoxide dismutase, and catalase. Fish that experienced EMS had significantly higher survival rates than those farmed in normal conditions (80.67% vs 61.33%). In conclusion, considering all measured parameters, 8-h light can be suggested as an optimum photoperiod for this fish species. Under 24L0D (no EMS) conditions, there were many negative effects apparent. In addition, a positive effect of EMS was evident in terms of survival after AC stress. AC stress decreased some health parameters under 24-h light treatment, while these results were not observed in EMS-exposed fish. Therefore, the EMS schedule can be a useful tool in preventing the negative effects of stress.