Effect of dietary tryptophan on blood and plasma parameters of striped bass Morone saxatilis, exposed to acute stressors

Striped bass, Morone saxatilis, is a marine species that belongs to the Moronidae family, which has great recreational and commercial importance and high production potential for human consumption. This research examines two acute stress factors that can be frequent in fish production units: a) handling is carried out constantly due to maintenance needs, size separation, growth evaluation, and health state, and b) hypoxia likely occur as the culture tank biomass, temperature, and fish metabolic rate increase. Juvenile fish (initial body weight 200 ± 3.0 g) were distributed in 110 L tanks and fed one week with different dietary tryptophan (Trp) levels: CD0.5 (0.5%), D1.0 (1.0%), D1.5 (1.5%) and D2.0 (2.0%). The fish were then exposed to stress by handling (5 min) or hypoxia (45 min). After that, blood hematocrit (Hct), hemoglobin (HB) and plasma cortisol, glucose (GLU), lactate (LACT), total protein (TP), albumin (AL), and globulin (GLOB) were analyzed, and AL/GLOB ratio was calculated. All analyzed parameters showed great sensitivity to acute stressors. Hypoxia increased Hct, cortisol, and GLU and decreased HB and LACT. Handling decreased HB and TP and increased GLU and LACT. D1.0 and D1.5 prevented Hct and LACT disturbance. D1.5 Trp prevented HB disturbance. All Trp supplemented diets prevented GLU change under hypoxia and TP change after handling. The results suggest that Trp played a role in M. saxatilis homeostasis restoration under acute stress.