title: Stress responses of the fish Nile tilapia subjected to electroshock and social stressors.
abstract: Plasma cortisol and glucose levels were measured in 36 adult Nile tilapia males, Oreochromis niloticus (standard length, mean +/- SD, 14.38 +/- 1.31 cm), subjected to electroshock and social stressors. Pre-stressor levels were determined 5 days after the adjustment of the fish to the experimental aquaria (1 fish/aquarium). Five days later, the effects of stressors on both cortisol and glucose levels were assessed. The following stressors were imposed for 60 min: pairing with a larger resident animal (social stressor), or a gentle electroshock (AC, 20 V, 15 mA, 100 Hz for 1 min every 4 min). Each stressor was tested in two independent groups, one in which stress was quantified immediately after the end of the 60-min stressor imposition (T60) and the other in which stress was quantified 30 min later (T90). Pre-stressor values for cortisol and glucose were not statistically different between groups. Plasma cortisol levels increased significantly and were of similar magnitude for both electroshock and the social stressor (mean +/- SD for basal and final samples were: electroshock T60 = 65.47 +/- 15.3, 177.0 +/- 30.3; T90 = 54.8 +/- 16.0, 196.2 +/- 57.8; social stress T60 = 47.1 +/- 9.0, 187.6 +/- 61.7; T90 = 41.6 +/- 8.1, 112.3 +/- 26.8, respectively). Plasma glucose levels increased significantly for electroshock at both time points (T60 and T90), but only at T90 for the social stressor. Initial and final mean (+/- SD) values are: electroshock T60 = 52.5 +/- 9.2, 115.0 +/- 15.7; T90 = 35.5 +/- 1.1, 146.3 +/- 13.3; social stress T60 = 54.8 +/- 8.8, 84.4 +/- 15.0; T90 = 34.5 +/- 5.6, 116.3 +/- 13.6, respectively. Therefore, electroshock induced an increase in glucose more rapidly than did the social stressor. Furthermore, a significant positive correlation between cortisol and glucose was detected only at T90 for the social stressor. These results indicate that a fish species responds differently to different stressors, thus suggesting specificity of fish stress response to a stressor.
authors.affiliation: Laboratório de Fisiologia e Comportamento Animal, Departamento de Fisiologia, Research Center on Animal Welfare (RECAW), Instituto de Biociências, Universidade Estadual Paulista, 18618-000 Botucatu, SP, Brazil.
authors.forename: R E
authors.initials: RE
authors.lastname: Barreto
authors.forename: G L
authors.initials: GL
authors.lastname: Volpato
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis*; D023681:Cichlids / Q000097:blood*; D004597:Electroshock; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D012930:Social Dominance; D013312:Stress, Physiological / Q000097:blood*
chemical_list: D001786:Blood Glucose; D006854:Hydrocortisone