Effect of increased liver glycogen and liver weight on liver function in rainbow trout, Salmo gairdneri Richardson: recovery from anaesthesia and plasma 35 S‐sulphobromophthalein clearance

. Juvenile rainbow trout (initial mean body weight 17 g) reared on practical trout diets containing different levels of available carbohydrate for 8–24 weeks were assayed for liver function based on the time required to recover from the anaesthetics tricaine methanesulphonate (MS222), 2‐phenoxyethanol (2PE) and tertiary‐amyl alcohol (TAA), as well as plasma clearance of 35 S‐sulphobromo‐phthalein (BSP), Liver/body weight ratios (LBW) and percentage liver glycogen content (LG) increased in a linear manner with increased available carbohydrate. The mean recovery time (MRT) of trout anaesthetized with 2PE and TAA increased linearly with increased LBW and LG. No difference was observed in the MRT of trout anaesthetized with MS222 which is not metabolized in the trout liver. There was a significant linear regression of the biological half‐life of plasma BSP on LBW (MR 2 = 95.7) and LG (MR 2 = 99.6). The results indicate that increased liver glycogen and liver weight due to higher levels of available carbohydrate affect the liver function of rainbow trout. These liver function tests may be applicable in determining acceptable levels of available carbohydrate in practical trout diets.