TRYPTOPHAN AS MODULATOR OF CORTISOL, GLUCOSA AND LACTATE LEVELS IN PLASMA OF Totoaba macdonaldi UNDER STRESS  

Miguel A. Cabanillas Gámez, Lus M. López Acuña, Mario A. Galaviz Espinoza,
Maricela Flores Ibarra y Conal D. True
 
Universidad Autónoma de Baja California (UABC)
Facultad de Ciencias Marinas (FCM)
PO Box 76, Ensenada BC 22800, México.
mcabanillas@uabc.edu.mx

Stress occurs in most organisms in response to physiological changes due to biotic or abiotic factors. Stress response as the organisms capacity to maintain their homeostasis. Tryptophan has been used in stress treatment in a large number of organisms for its role as a serotonin precursor and hypothalamic-pituitary- interrenal axis (HHI) modulator, which regulates the stress response. The aim of this study was to determine the effect of dietary tryptophan level on stress response in juvenile Totoaba macdonaldi.

A group of totoaba juveniles with an average weight of 90 ± 5.0 g were distributed in 12 tanks of 500 L in recirculating system. Four diets with different tryptophan levels (0.5, 1.09, 1.69 and 2.28%) were formulated. At the end of experiment fish from each tank were divided into four groups and each group was exposed to one of following stress conditions: Management (persecution), hypoxia (5 mg L-1 de O2) and ammonium (5 mg L-1) and an additional control group. After stress condition, fish were anesthetized and bled by cardiac puncture. Plasma cortisol level (EIA 1887 DRG), lactate (L-Lactate Assay Kit ab65331 Abcam) and glucose (Pointe Scientific, Inc.) was determined. Two way ANOVA was performed using the Sigma Plot 12.5 packet with a significance level α = 0.05.

Plasma levels of cortisol, glucose and lactate have been used as stress indicators in other fish species. Totoaba values are shown in Table I. No significant differences in plasmatic cortisol level were observed for effect of different stress; however, significant level of cortisol increased (P = 0.044) with tryptophan diet of 1.09% compared with control diet (0.5%). This may be related to increased activity of HHI axis. Significant increase of glucose and lactate levels were observed in hypoxic and management condition, however, not significant differences (P= 0.599 y 0.146 respectively.) were observed for diets.

Cortisol, glucose and lactate concentration are shown as physical stress indicators for totoaba. Tryptophan 1.09% diet had an effect on stress response, indicated by significant increase of plasma cortisol levels.