Fig. 4. (A) Thermal plasticity of Mg²⁺-Ca²⁺ myofibrillar ATPase activity acquired during ontogeny in the common carp. The time course of changes in enzymic activity was longer for juveniles at 14 weeks (purple) than at 20 weeks (green) post-hatch. The blue and red shaded areas represent the myofibrillar ATPase activity of 120 mm total length (TL) 10°C- and 21°C-acclimated carp respectively. The lengths of the fish during the experiment are indicated with colour-coded arrows. (B,C) Changes in myosin heavy chain (MyHC) peptide maps (top) and their densitometric scans (bottom) with age and acclimation temperature. Bands characteristic of 21°C-acclimated and 10°C-acclimated fish are indicated by left- and right-facing arrowheads, respectively. The MyHC composition characteristic of cold acclimation was not observed in any fish greater than 37 mm total length. Adapted from Cole and Johnston (2001).