Muscle fibre number varies with haemoglobin phenotype in Atlantic cod as predicted by the optimal fibre number hypothesis

• Published in: Biology Letters
• Main Authors: Johnston, Ian A, Abercromby, Marguerite, Andersen, Øivind
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2006
• Subjects: Norway; atlantic cod; Gadus morhua; Northern Norway
• Online Access: https://doi.org/10.1098/rsbl.2006.0500; https://royalsocietypublishing.org/doi/pdf/10.1098/rsbl.2006.0500; https://royalsocietypublishing.org/doi/full-xml/10.1098/rsbl.2006.0500

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 (FN max ) 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.