title: Muscle fibre number varies with haemoglobin phenotype in Atlantic cod as predicted by the optimal fibre number hypothesis.
abstract: Atlantic cod (Gadus morhua L.) with the HbI-(2/2) haemoglobin phenotype have a higher blood oxygen affinity at low temperatures and a lower routine metabolic rate than individuals with the HbI-(1/1) phenotype. In the present study, muscle structure was found to be related to haemoglobin phenotype in a coastal population of Atlantic cod from the Saltenfjord region of Northern Norway. The maximum number of fast muscle fibres (FNmax) was reached at approximately 39 cm fork length and was 15% greater in the HbI-(1/1) than in the HbI-(2/2) phenotypes whereas the average fibre diameter for fish of the same fork length was significantly lower. Theoretically, the higher oxygen affinity of the HbI-(2/2) phenotype in the cold water of northern latitudes could have resulted in a relaxation of diffusional constraints at the level of individual muscle fibres, permitting the observed increase in fibre diameter. The results support the optimal fibre number hypothesis which envisages a trade-off between diffusional constraints and the energy cost of maintaining ionic homeostasis with fewer larger diameter muscle fibres in the HbI-(2/2) phenotype contributing to a lower routine metabolic rate.
authors.affiliation: School of Biology, University of St Andrews, St Andrews, KY16 8LB, UK. iaj@st-and.ac.uk
authors.forename: Ian A
authors.initials: IA
authors.lastname: Johnston
authors.forename: Marguerite
authors.initials: M
authors.lastname: Abercromby
authors.forename: Oivind
authors.initials: O
authors.lastname: Andersen
mesh_terms: D000818:Animals; D049628:Body Size / Q000502:physiology; D048389:Gadus morhua / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology; D006454:Hemoglobins / Q000235:genetics / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000235:genetics; D018485:Muscle Fibers, Skeletal / Q000648:ultrastructure; D009664:Norway; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary
chemical_list: D006454:Hemoglobins; D008562:Membrane Glycoproteins; C026236:hemoglobin I, non-mammalian