Histochemical characterization of myotomal muscle in the bluntnose minnow, Pimephales notatus Rafinesque

A histochemical study of the axial muscles in the bluntnose minnow, Pimephales notatus Rafinesque, revealed three main types of fibres‐red, white and pink. These were distin‐ guished on the basis of glycogen or lipid contents, or of NADH diaphorase and actomyosin ATPase activities. White muscle formed the largest fraction of the total, whereas red ranged from slightly > 1% of the total cross‐sectional area in the immediately post‐pectoral fin region to slightly <4% in the post‐anal region. Pink muscle formed only a few layers of fibres between red and white. Results are discussed in relation to possible division of labour among the different types of fibres. However, it is emphasized that fibre types may be more functionally versatile in fish muscles than has frequently been supposed.