Determination of optimal fasting time before blood sampling to get baseline data on serum biochemical characteristics in juvenile turbot (Scophthalmus maximus)

Serum biochemical characteristics provide crucial information about the physiological condition of fish and are greatly affected by the sampling conditions. This study examined the effects of short-term fasting periods [in terms of degree-days (°C days)] on the serum biochemical parameters of juvenile turbot (Scophthalmus maximus) and revealed the optimal fasting time before blood sampling to obtain the baseline data. Stomach content index (SCI), digestive somatic index (DSI), viscerosomatic index (VSI), hepatosomatic index (HSI), serum thyroid hormones (thyroxine, T4; triiodothyronine, T3), cortisol, glucose, lactate, cholesterol, triglyceride, high-density lipoprotein, low-density lipoprotein, total protein, albumin, globulin and albumin/globulin level of juvenile turbot were determined after different fasting durations (0, 0.25, 0.5, 1, 2 and 3 days). Results showed that the levels of SCI, T4, T3, cortisol, glucose, lactate, cholesterol, and triglycerides were significantly affected during fasting, whereas the levels of SCI, glucose, lactate, cholesterol, triglyceride were not significantly different at 1 (16.5 °C days), 2 (31 °C days), and 3 days (48 °C days) of fasting. Meanwhile, no significant difference was found for T4 and T3 at 1 day (16.5 °C days) and 2 days (31 °C days) of fasting, and for cortisol at 1 day (16.5 °C days) and 3 days (48 °C days) of fasting. However, DSI, VSI, HSI, high-density lipoprotein, low-density lipoprotein, total protein, albumin, globulin and albumin/globulin levels remained unchanged and showed no significant difference. These results indicate the importance of fasting period on the digestive system and serum biochemical properties of turbot. Therefore, based on these results and considering the fish management, 1 day (16.5 °C days) is the best fasting period prior to blood collection from juvenile turbot for blood biochemistry determination.