Modification of the Plasma Cortisol Response to Stress in Rainbow Trout by Selective Breeding

Abstract

The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. ABSTRACTMale and female rainbow trout were segregated into high-and low-responding individuals (HR, LR) on the basis of their plasma cortisol response to a 3 h period of confinement imposed at five, monthly, intervals. Consistent divergence was obtained in the responsiveness of the two groups, although the difference between LR and HR groups was greater in female fish (56 c.f. 116 ng ml -1 ) than in males (45 c.f. 69 ng ml -1 ). Progeny groups (full-sib families) were obtained from the pairing of HR males and females and LR males and females. A third progeny group (US) was obtained by random pairing of parents which were not selected as HR or LR. Post-stress plasma cortisol levels in the progeny were first tested at 6 months after hatch and were significantly correlated with the response of the corresponding parental groups, HR>US>LR (178, 126, 81 ng ml -1 respectively). The difference in responsiveness between LR and HR groups was demonstrated in all four subsequent tests over a 12 month period. There were no significant differences in baseline plasma cortisol levels in LR and HR groups prior to confinement. During a 4h period of confinement, the differences in plasma cortisol levels between LR and HR fish were sustained throughout, indicating that the trait upon which the fish were selected was related to absolute maximum levels of circulating cortisol, not the rate of change of cortisol levels during exposure to a stressor. A moderately high heritability (h 2 ) for confinement-induced plasma cortisol of 0.41 was obtained by a parent-progeny regression. Manipulation of stressresponsiveness in fish by selective breeding offers scope for optimising performance under intensive rearing conditions but also provides a useful research tool for investigating the operation of the endocrine stress response.3

Stress Responsiveness Affects Dominant–Subordinate Relationships in Rainbow Trout

“…Among the F2 fish the divergence of cortisol responsiveness to a confinement stressor, which was evident in the F1 high-and low-responding parents, was maintained. The heritability of this trait, derived from a mid-parent versus progeny regression, was high (h 2 = 0.6) and consistent with that reported in previous studies (h 2 = 0.4 -0.6; Fevolden et al, 1999;Pottinger and Carrick, 1999b). …”

“…During previous studies (Pottinger and Carrick, 1999b), the two F1 families of rainbow trout that displayed the most divergent mean plasma cortisol response to a 3 h period of confinement were identified. During June 1999 25 fish were randomly netted in batches of five from each of two holding tanks (1000 liters capacity, circular glass fiber, supplied with a constant flow of lake water at 30 l min -1 at ambient temperature) containing LR fish (mean weight  SEM, 859  19 g, n = 50) and transferred to anesthetic (2-phenoxyethanol, 1:2000).…”

“…In rainbow trout (Oncorhynchus mykiss Walbaum) the magnitude to which plasma cortisol is elevated following exposure to a stressor is a stable trait (Pottinger, Pickering and Hurley, 1992) with a moderate to high degree of heritability (h 2 = 0.4 -0.6; Fevolden, Røed, Fjalestad and Stien, 1999;Pottinger and Carrick, 1999b). These attributes have facilitated the selective breeding of two lines of trout (high-responding -HR; low-responding -LR) with divergent cortisol responsiveness to a standardized confinement stressor (Pottinger and Carrick, 1999b).…”

The effect of allostatic load on hypothalamic–pituitary–interrenal (HPI) axis before and after secondary vaccination in Atlantic salmon postsmolts (Salmo salar L.)

“…For instance might different genetic strains exhibit different resting levels (baseline) of cortisol due to the effects at any levels in the HPI axis (Fevolden et al 2002;Pottinger and Carrick 1999;Tanck et al 2002;Tanck et al 2001). Each level of the axis (hypothalamus, anterior pituitary, interrenal cells) is subjected to opposite influences, trophic via their respective stimulating inputs (such as CRH to the pituitary or ACTH to the interrenal cells) and inhibitory via corticosteroid hormones (negative feedback) (Mormede et al 2007).…”

Breeding for robustness: the role of cortisol

“…Pig populations show much functional variation (e.g. Foury et al, 2007)) and divergent genetic selection for the HPA axis response to various stimuli has been successful in a wide range of species: trout (confinement stress: (Fevolden et al, 1999;Pottinger and Carrick, 1999), chickens (adrenal response to ACTH: (Edens and Siegel, 1975); social stress: (Gross and Siegel, 1985), turkeys (cold stress: (Brown and Nestor, 1973), Japanese quail (immobilization stress: (Satterlee and Johnson, 1988) and mice (restraint stress: (Touma et al, 2008). The response to selection is usually very strong, with realized heritability between 0.4 and 0.5.…”