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Contains fulltext : 169006.pdf (publisher's version ) (Open Access)

The brain monoamines serotonin (5-hydroxytryptamine; 5-HT) and dopamine (DA) both play an integrative role in behavioural and neuroendocrine responses to challenges, and comparative models suggest common mechanisms for dietary modulation of transmission by these signal substances in vertebrates. Previous studies in teleosts demonstrate that 7 d of dietary administration with l-tryptophan (Trp), the direct precursor of 5-HT, suppresses the endocrine stress response. The present study investigated how long the suppressive effects of a Trp-enriched feed regimen, at doses corresponding to two, three or four times the Trp levels in commercial feed, last in juvenile Atlantic cod (Gadus morhua) when the fish are reintroduced to a diet with standard amino acid composition. We also wanted to determine whether Trp supplementation induced changes in brain monoaminergic neurochemistry in those forebrain structures innervated by DA- and 5-HTergic neurons, by measuring regional activity of DA and 5-HT in the lateral pallial regions (Dl) of the telencephalon and nucleus lateralis tuberis (NLT) of the hypothalamus. Dietary Trp resulted in a dose-dependent suppression in plasma cortisol among fish exposed to confinement stress on the first day following experimental diet; however, such an effect was not observed at 2 or 6 d after Trp treatment. Feeding the fish with moderate Trp doses also evoked a general increase in DA and 5-HT-ergic activity, suggesting that these neural circuits within the NLT and Dl may be indirectly involved in regulating the acute stress response

Competition over limited resources can lead to serious injury and may be minimized by the formation of social hierarchies. However, there are often physiological consequences associated with social status which can affect both dominant and subordinate animals. In salmonid fish, at least under laboratory conditions, physiological costs are mainly associated with subordinance. The structure of hierarchies formed among salmonids in the laboratory is likely to be different from those formed in complex natural environments, and yet little is known about the physiological consequences of dominance in the field. We tested the hypothesis that there are specific physiological correlates associated with specific social behaviours among natural populations of juvenile salmonid fish by observing brown trout, Salmo trutta, in small streams. Fish were tagged and their behaviour observed by video recording over several weeks at three sites along Devonport Leat (Devon, U.K.). Although diet and tissue metal concentrations differed between sites, the behaviour of the fish at the three sites was very similar. At the end of the observation period, we sampled fish for parameters including specific growth rate, plasma cortisol and osmolality, brain monoamines and gut contents. There was no relationship between social status and growth rates but, contrary to laboratory predictions, dominant fish had higher plasma cortisol. We conclude that physiological correlates of dominance do exist among these natural fish populations but they may differ to those found in the laboratory. Further research is now required to test a wider range of physiologies in the field.

In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability, and high responding (HR) and low responding (LR) lines of rainbow trout have been generated by individual selection for consistently high or low post-stress cortisol values. In addition to post-stress plasma cortisol concentrations these rainbow trout strains differ in several other traits. For instance, sympathetic reactivity shows an opposite pattern as compared to plasma cortisol, LR trout responding to acute stress with larger increase in plasma catecholamine levels than HR trout. Moreover, this differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. The LR strain tends to show proactive behaviors such as enhanced aggression, social dominance, and rapid resumption of feed intake after stress whereas the HR strain display more of a reactive behavioral profile. Furthermore, differences gene expression profiles and brain monoamine neurochemistry have also been reported in these lines. Studies on the HR and LR trout lines may provide a physiological and genetic basis for new marker-assisted selection strategies in the finfish aquaculture industry, as well as increased knowledge of the function and evolution of central neuroendocrine signaling systems.

The overall aims of the project is to identify, in sea bream, sea bass, oyster, and rainbow trout, genes of which expression is associated with disease and stress resistance and to develop genetic approaches that allow characterisation of genetic markers for marker-assisted selective breeding of disease and/or stress resistant individuals. For such project, the following main objectives have to be reached

Juvenile rainbow trout divergent in their cortisol response to confinement stress (HR: high responsive or LR: low responsive fish) were exposed to either 1 or 3 h of confinement stress. Untreated fish served as control. After the exposure blood and brain samples were collected. From the blood samples, the levels of cortisol and catecholamines were determined, while the brain serotonergic and monoamineoxidase (MAO) activity was determined in four different brain areas (brain stem, hypothalamus, telencephalon and optic tectum). Our results show that the LR fish responds to handling stress with a higher increase in plasma epinephrine compared to HR fish. Our results also show that confinement stress leads to a larger increase in the serotonergic activity in the brain stem and telencephalon in LR fish compared to HR fish. These results support the hypothesis that stress coping strategies similar to those described in mammals also exists in fish. Further, our results have shown that the MAO activity increases in optic tectum and hypothalamus of rainbow trout during confinement stress, while it remains unchanged or decreases in brain stem and telencephalon. Moreover, the MAO activity does not differ between the two selection lines. This indicates that MAO participates actively in the stress response without contributing to the differences in stress coping strategies

Individuals of rainbow trout Oncorhynchus mykiss with a low cortisol response to stress showed higer locomotor activity compared to individuals with a high cortisol response

The three-spined stickleback Gasterosteus aculeatus is an intermediate host of the tapeworm Schistocephalus solidus. Changes in predator avoidance, foraging and shoaling behaviour have been reported in sticklebacks infested with S. solidus, but the mechan, Addresses: Overli O, Uppsala Univ, Dept Anim Dev & Genet, Evolutionary Biol Ctr, Norbyvagen 18A, SE-75236 Uppsala, Sweden. Uppsala Univ, Dept Anim Dev & Genet, Evolutionary Biol Ctr, SE-75236 Uppsala, Sweden. Uppsala Univ, Dept Comparat Physiol, Evolution

Sexually mature Arctic charr (Salvelinus alpinus) males were allowed to interact in pairs for 4 days in the absence of females. Agonistic behavior was quantified, and at the end of the experiment, plasma levels of glucose, cortisol, testosterone (T), 11-ketotestosterone (11-KT), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha, 20beta-P) were determined alongside brain concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA, the major 5-HT metabolite), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC, a major DA metabolite). Plasma cortisol and glucose were significantly elevated in subordinate fish, and the number of aggressive acts received showed positive correlations with plasma levels of glucose on day 1, during the development of the dominance relationship, and of cortisol on day 4, when the dominance relationship was established. In contrast, plasma concentrations of T and 11-KT were significantly higher in dominant than in subordinate males, and there was a similar tendency in plasma concentrations of 17alpha,20beta-P. Further, plasma levels of these gonadal steroids were correlated with the number of aggressive acts performed on day 4, but not with the number of aggressive acts received. The plasma cortisol concentrations did not correlate with either 5-HIAA:5-HT or DOPAC:DA ratios in any of the brain parts analyzed. Plasma glucose levels showed positive correlations with brain 5-HIAA:5-HT ratios. Negative correlations were observed between 5-HIAA:5-HT ratios in the optic tectum and between plasma levels of T, 11-KT, and 17alpha,20beta-P. Telencephalic DOPAC/DA ratios displayed a negative correlation with plasma levels of T, 11-KT, and 17alpha,20beta-P, but only in dominant males.

Offspring of wild and sea-ranched [domesticated) sea trout (Salmo trutta) originating from the same river, were reared under identical hatchery conditions from the time of fertilization. At one year of age individual fish were exposed to two standardized, Addresses: Winberg S, Uppsala Univ, Dept Comparat Physiol, Evolutionary Biol Ctr, Norbyvagen 18A, SE-75236 Uppsala, Sweden. Natl Board Fisheries, Inst Freshwater Res, Lab Streamwater Ecol, Alvkarleby, Sweden. Univ Stockholm, Div Populat Genet, Stockholm