Effects of dietary barley on rainbow trout exposed to an acute stress challenge

Abstract

[EN] The present study evaluates the effect of dietary barley, based on its potential stress-relieving properties, on rainbow trout under acute stress challenge (hypoxia and crowding) and their recovery. Diets were formulated containing increasing barley concentrations (0, 4, 8, 16, 32%). Cortisol on plasma and fin, glucose and lactate plasma levels and malondialdehyde (MDA) in muscle were determined under normoxia before the stress test (basal levels), 30 min after the acute stress challenge and also during normoxia recovery (6 and 12 h after the stress). Results showed that at basal levels the inclusion of barley had no influence on cortisol, glucose nor on lactate values. After 30 min from the stress challenge, there was a significant increase in cortisol, glucose and lactate concentration in fish of all groups. Plasma cortisol showed the lowest levels in fish fed with diets at a medium (8%) of barley concentration and returned to basal levels 6 h after the stress stimulus with no differences between diets. Glucose values showed a less clear tendency 30 min after the stress challenge with lower levels in the control group, fish fed with 8% and 32% of barley in the diets and returned to basal levels in almost all the groups only 12 h after the stress challenge. Lactate showed the same trend as with glucose after the stress challenge but it returned to basal levels in 6 h. Interestingly, there was a significant decrease of lipid oxidation (MDA) in muscle soon after the stress test of fish fed with the highest barley levels. The present results suggest a potential positive effect of dietary barley on trout stress response.