The outcome of agonistic interactions in social animals is depending on several different factors. One of the factors involved is the hypothalamic-pituitary-interrenal (HPI) axis. In addition to its endocrine effects on the HPI axis corticotropin releasing hormone (CRH) is also known to affect behaviour. In our study we investigated the effect of CRH on agonistic interaction in rainbow trout (Oncorhynchus mykiss). Fish weighing 105.1 ± 29.3g (mean ± SD) were kept isolated for one week, after which CRH or the CRH antagonist a-helical CRH_1-41 (ahCRH) was administrated through intracerobroventricallary (ICV) injection, and the fish were allowed to interact with a weight matched control (given saline ICV) for 1 hour. Two doses of CRH and ahCRH were used, 0.5 and 1.0 mg for CRH, and 1.0 and 2.0 mg for ahCRH. The doses were dissolved 1ml saline, which was the injection volume. Behaviour during the fights was quantified and dominance noted at the end. Blood plasma was analysed for cortisol. The injection of 1.0 mg CRH had a significant effect on social rank, the CRH treated fish becoming subordinant. CRH injection as well as becoming subordinate following social interaction resulted in significantly elevated plasma cortisol levels. These results suggest that CRH affects social behaviour through central effects.

Funded by The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS)