In a context of global change and increased food demand, the growth of aquaculture production must guarantee animal welfare. Handling or transport operations activate the stress responses, wh ich may compromise the integrity and general welfare status of fish. To improve these processes, the use of anaesthetics has been proved useful to reduce the possible adverse effects.
MS-222 or benzocaine are s ynthetic chemicals commonly employed as anaesthetics in aquaculture. H owever, their use is controversial due to human safety issues and the physiological side- effects that induce in fish. Essential oils (EOs) derived from plants have been studied for this purpose, but its use might be problematic because of its compositional variability and effectiveness. Therefore, the use of synthetic nature-identical compounds (such as eugenol, menthol or thymol) , the bioactive molecules naturally present in tho se EOs, is a promising approach to develop new se dative strategies to improve operational processes in aquaculture.
For this purpose, th is study assesses the effectiveness of a prototype with sedative properties (TecV2, developed by TecnoVit-FARMFaes Ltd.) in seabass (Dicentrarchus labrax) for a live transport of 3 and 6 hours.
Materials and methods
Seabass juveniles ( D. labrax) ( n = 72 , weight = 48.9 ± 18.4 g ) were placed into 15 L-tanks and distributed in four different experimental groups in triplicate : i ) 3 h transport without sedation (CTRL-3H) ; ii) 3 h transport with 10 ppm of TecV2 prototype; iii) 6 h transport without sedation ; and iv ) 6 h transport with 10 ppm of TecV2 prototype. Prototype concentration was selected according to previous tests.
Transport simulations took 3 and 6 h respectively . At the end of stressing trials, half of the animals from each tank were euthanized and sampled (n = 9). The remaining fish were transferred in to clean water tanks to determine their status after 24 h of recovery. Additionally, 9 fish were euthanized and sampled before any manipulation (basal conditions). Fish were euthanized with an overdose of 2-phenoxyethanol (1 ppt ). Plasma s amples were taken to determine changes on plasmatic secondary stress responses (cortisol , glucose, lactate, etc.). Liver was also excised to assess changes in the intermediary metabolism of amino acids, lipids and carbohydrates.
Tanks were well aerated every 90 min until oxygen full-saturation. Oxygen levels were monitor ed and remained above 5 ppm during the whole simulation periods. Temperature was also monitored and remained around 19 ± 1 ºC.
Our results showed that both live transport simulations for 3 and 6 h, were effective to activate stress responses in the seabass juveniles ( D. labrax) . Furthermore, these responses were modulated by t he addition of the sedative prototype TecV2 to the water.
After 3 h transport an increase on plasmatic glucose was observed, a common secondary stress response triggered by cortisol elevation. However, t his response was ameliorated by the use of TecV2 , together induced a reduction on lactate and protein levels.
The 6 h transport induced a greater disturbance on stress parameters. At this point, non-sedated fish ha d overco me stress situation, so plasma hyperglycaemia was not detected . However, this response was observed on sedated fish after 6 h of transport, probably because of TecV2 sedation effect was lowering . Protein and triglycerides (TAG) levels were lower in non-sedated fish , so TecV2 was useful to maintain these energetic sources in plasma. Alternatively, amino acids levels did not return to initial values after recovery and values were even lower than those observed during stress. However, the r eduction after recovery on amino acids levels was lower when TecV2 was used. Hepatic carbohydrate and l ipid metabolism was also altered and an increase on TAG levels after 24 h was observed. These results are in concordance with the results of enzymatic activity determined.
In conclusion, TecV2 has the potential to be used as sedative for the live transport of seabass juveniles, especially for a 3 h transport, since it reduces energy mobilization.
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