Subtle temperature increase can interact with individual size and social context in shaping phenotypic traits of a coldwater fish.

Temperature and individual egg size have been long studied in the development of fishes because of their direct effects on individual fitness. Here we studied the combined effects of three important factors for fish development, i.e. egg size, social environment and water temperature. Arctic charr (Salvelinus alpinus), a coldwater fish known to be phenotypically plastic, was used to investigate how these factors may affect growth and foraging behaviour of juvenile fish in a benign environment. We accounted for the social environment during early development by comparing fish raised in groups and in isolation. We examined the effect of egg size and a 2 °C difference on foraging behaviour, activity and growth a few weeks after first feeding. Growth trajectories of fish originating from large and small eggs were similar within each temperature: larger fish coming large eggs were at all time larger than smaller fish. There was no indication that small fish raised at a higher temperature grew faster than larger fish raised at a lower temperature. A 2 °C difference in temperature affected the behaviour of fish differently according to body size and/or social context. The foraging probability difference between fish raised in groups and fish briefly isolated was higher at 4.5 °C than at 6.5 °C for both size fish. Finally, there was no repeatability in foraging behaviour and mobility for isolated individuals. These results highlight the importance of small changes in temperature when evaluating growth and behaviour of fishes, and reveal the importance of considering the interaction of temperature with other factors, e.g. individual size and social environment, especially at early stages of development in fishes. We discuss these findings in the context of rapid changes in temperature and how temperature and its interaction with other factors may affect the phenotypes, ecology and evolution of coldwater fishes.

Evidence for the catalysis of dextromethorphan O-demethylation by a CYP2D6-like enzyme in pig liver.

The pig is increasingly being used in pharmacological and toxicological studies, and is the species of choice for future research into xenotransplantation, extracorporeal liver support and hepatocyte-based bioartificial liver. However, relatively little is known about xenobiotic-metabolizing enzymes in this species. In the present study, immunoblotting with polyclonal anti-rat and anti-human cytochrome P450 (CYP) antibodies revealed the presence of proteins in pig liver which cross-reacted with anti-human CYP1A2, CYP2D6 and CYP3A4, and with anti-rat CYP2E1 antibodies. Northern blot analysis demonstrated the presence of mRNA which hybridized to cDNA probes for human CYP2D6, CYP2E1 and CYP3A4, and to an oligonucleotide probe for pig CYP3A29. As there is a lack of a good animal model for CYP2D6, the presence of a CYP2D6-related protein in pig liver was of particular interest. Pig hepatocytes also demonstrated CYP2D6 immunoreactive protein, and mRNA hybridizable to a CYP2D6 cDNA probe. We investigated the ability of pig liver microsomes to catalyse dextromethorphan O-demethylation, a widely-used marker enzyme activity for CYP2D6. This enzyme activity demonstrated biphasic kinetics, with a high affinity apparent K(m1)=6.9+/-3.6 microM and V(max1)=10.5+/-6.1nmol/min/nmol CYP. The reaction was sensitive to inhibition by the CYP2D6-selective inhibitors quinidine, quinine, lobeline and norfluoxetine, whereas chemical inhibitors selective for other CYP isoforms failed to affect the reaction. We conclude that dextromethorphan O-demethylation is catalysed by a CYP2D enzyme which is remarkably similar to human CYP2D6, suggesting potential value of the pig as a model for predicting human metabolism of xenobiotics which undergo CYP2D6-dependent biotransformation.