Interaction of dietary energy levels and culture density on growth performance and metabolic and oxidative status of rainbow trout (Oncorhynchus mykiss)

•High culture density negatively affected trout growth when fed on the lower energy diet.•It also causes oxidative stress in liver and decreases hepatic and muscular metabolic activities.•High energy intake adversely affects hepatic G6PDH activity and oxidative stress in trout muscle.•Combination of a high stocking density and the feeding on a high energy diet seems to harm the fish physiology and welfare. Rainbow trout (100g initial weight) were subjected to the combined effect of two culture densities (15 and 40kgm−3, D15 and D40, respectively) and two dietary energy levels (22 and 27MJkg−1 E22 and E27, respectively) during a 75-days experimental period. At the end of the experiment, the growth rate as well as the metabolic and oxidative status of liver and muscle of fish were studied. The results showed that combination of culture density and dietaryenergy level negatively affected growth, cholesterol and LDL plasma levels and oxidative stress in muscle. Higher culture density negatively affected the values of total protein, triglycerides, and HDL in plasma, values of hepatic and muscular metabolic activities pyruvate kinase (PK), citrate synthase (CS), and hydroxiacil-CoA dehydrogenase (HOAD); glutamate pyruvate transaminase (GPT) and glutamate oxaloacetate transaminase (GOT) activities in plasma, liver, and muscle; glucose 6P dehydrogenase (G6PDH) activity in muscle; and oxidative stress in liver. High energy intake, adversely affected the hepatic activity of G6PDH, HOAD, GPT and oxidative stress in muscle. Consequently our results indicate that a combination of high culture density and a high level of dietary energy (27MJkg−1 in diet) exert a negative impact on the physiology and consequently on the welfare of the farmed fish.