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. Prestressor 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.

Essential oil of Aloysia triphylla in Nile tilapia: anaesthesia, stress parameters and sensory evaluation of fillets

“…In previous studies, plasma cortisol levels in non‐stressed Nile tilapia ranged from 16.43 to 65.67 ng mL −1 (Volpato & Barreto ; Biswas, Maita, Yoshizaki & Takeuchi ; Barreto & Volpato ), similar to our results with EOAT. Cortisol is widely used as both a long‐ and short‐term primary stress indicator (Maricchiolo & Genovese ).…”

Stress hyperglycemia: an essential survival response!

“…Insects, worms and all verterbrates, including fish, develop stress hyperglycemia when exposed to stress [17,18]. In animal models of hemorrhagic shock the administration of a hypertonic glucose solution increased cardiac output, blood pressure and improved survival [19].…”

Are personality traits consistent in fish?—The influence of social context

“…In addition, Ruiz-Gomez et al (2008) suggest that genetic differences determine social position in early life, whereas some behavioural components of coping styles can be modified by social experience, Moreover, we can also assume that this lack of behaviour consistency measured on proactive and reactive groups, may not represent a "loss" of personality in some individuals, but are instead the reflection of stressors such as social stress. Some species develop strong social hierarchies (Barreto Volpato 2006;Ejike and Schreck 1980;Fox et al 1997) that may cause changes in personality types according to the available social information in the group. Koolhaas and Boer (2008) showed that groups of proactive individuals may encourage a higher level of aggressiveness and fights so that dominant individuals can keep their position in the group.…”