Plasticity of myosin heavy chain expression with temperature acclimation is gradually acquired during ontogeny in the common carp (Cyprinus carpio L.).

Common carp (Cyprinus carpio L.) were reared from hatching until 61 mm total length (TL) at 21 degreesC. At 14 weeks and 20 weeks post-hatch, corresponding to initial lengths of 30 mm and 44 mm respectively, fish were acclimated to 10 degreesC using a rate of cooling of 1 degreesC per day. A statistical model was used to compare the time course in the change of white muscle myofibrillar ATPase activity with temperature acclimation. The myosin heavy chain (MHC) composition of white muscle myofibrils was investigated using peptide mapping. A significant increase in myofibrillar ATPase activity was observed after 2-3 weeks in the 44 mm group, but not until 4-5 weeks in the 30 mm group, when they had reached 37 mm TL. The MHC banding pattern of 120 mm TL fish acclimated to 10 degreesC or 21 degreesC for a minimum of 6 weeks were distinct from each other. The MHC peptide map characteristic of 10-degreesC-acclimated fish was not observed in individuals less than 37 mm length. We therefore conclude that the capacity to alter the composition and properties of myofibrils with cold acclimation is acquired in juvenile carp at around 37 mm TL.