A histochemical, light and electron microscopic examination of eel, Anguilla rostrata red and white muscle

The histochemical and structural properties of red and white muscle from the American eel, Anguillu rostrata , are examined. The results suggest that in addition to the classic red and white fibre types, with the generalized pattern of SDH, LDH and myosin ATPase activities, the eel also has two further fibre types. Both are localized directly adjacent to the perimysium separating the red and white muscle masses: one is found only in white myotomes at the lateral line, while the other is unique to red myotomes. During the transition from immature yellow to mature bronze eels, the red muscle myofibrils become partitioned as a result of increases in mitochondria1 numbers and lipid content. It is suggested (1) the myofibrillar partitioning may reflect an altered functional role of red muscle and (2) eel white muscle may provide a portion of the muscular power required to sustain cruising speeds necessary for the long seaward migration of this animal.