Effect of the establishment of dominance relationships on cortisol and other metabolic parameters in Nile tilapia (Oreochromis niloticus)

Abstract

The objective of the present study was to investigate the influence of the establishment of dominance relationships and social stress on plasma cortisol and metabolite levels in Nile tilapia (Oreochromis niloticus). During the 30-day experiment, the fish weighing 236 ± 29 g were kept in individual aquaria, except for two pairings lasting 6 h each. Blood samples were taken from the animals before and after pairing. Display, approach, attack, rebuff, chase flight, and coloration were carried out on days 16 and 30. Activities and behaviors characteristic of the establishment of dominance relationships were described. It was possible to classify all experimental fish (N = 30) as dominant or subordinate. No differences were detected between dominant (N = 15) and subordinate (N = 15) fish during isolation or after pairing in cortisol (isolated: 5.76 ± 0.98 vs 5.42 ± 0.63; paired: 10.94 ± 1.62 vs 11.21 ± 2.45 µg/dl), glucose (isolated: 60.02 ± 4.9 vs 67. 85 ± 16.16; paired: 110.44 ± 15.72 vs 136.26 ± 22.46 mg/dl), triglyceride (isolated: 167.87 ± 5.06 vs 185.68 ± 7.24; paired: 210.85 ± 13.40 vs 221.82 ± 12.70 mg/dl) or total protein levels (isolated: 7.01 ± 0.42 vs 6.69 ± 0.59; paired: 9.21 ± 0.62 vs 9.51 ± 0.66 g/dl). However, when isolated (N = 30) and paired (N = 30) tilapia were compared, there were significant differences in cortisol and metabolite levels. The similar response presented by dominant and subordinate tilapia indicates that establishment of dominance relationships was a stressor for both groups.

Stress responses of the fish Nile tilapia subjected to electroshock and social stressors

“…Mean pre-stressor cortisol levels ranged from 41.57 to 65.67 ng/mL (Figure 2), in agreement with other studies. For instance, the baseline described for O. niloticus ranged from ~5 to 60 ng/mL (10,11,17,23,24), and for the related Cichlid, O. mossambicus, it ranged from ~20 to 60 ng/mL (33), and from about 10 to 60 for other fish species (3)(4)(5)(6)19,34).…”

“…Both previous residence (28) and larger body size (29) are associated with dominance. This procedure guaranteed a clear dominance-subordinance relationship, thus characterizing a typical situation of social stress for the focal fish (9,11,23,25). To evaluate the social stressor, agonistic acts were quantified based on the ethograms described by Alvarenga and Volpato (12), Giaquinto and Volpato (25) and Barki and Volpato (26) for this species.…”

“…Stress is a generalized response attributed to the fact that fish commonly have a complex of adaptive reactions to cope with stressors (1,2). For instance, stress has been reported to elevate plasma cortisol (3)(4)(5)(6)(7)(8), glucose levels (5,6,(9)(10)(11), and ventilatory frequency (12)(13)(14)(15) in fish. Although stress can be considered to be a generalized response, it can be modulated by specific stressor conditions (16).…”

“…We chose the fish species Nile tilapia, Oreochromis niloticus, because it is an important fish model for studying the stress response (9)(10)(11)(12)(13)17,21,23,24) and has evident agonistic behavior (11,12,22,25,26), both aspects related to the proposed hypothesis.…”

Correlations Between Pre- and Post-Fasting Growth in Nile Tilapia

“…For instance, larger body size is associated with less vunerability to predators (Brown and Braithwaite, 2004) and dominance (Turner and Huntingford, 1986). Nile tilapia is a territorial cichlid species that organize themselves into hierarchy of dominance (Corrga et al, 2003;Barreto and Volpato, 2006a;b). Dominance hierarchies result in unequal distribution of resources, with dominant individuals able to monopolize the resources (Harwood et al, 2003).…”