Characterization of the swimming muscle of the anchovy Engraulis anchoita (Hubbs and Martini 1935).

The lateral muscle characteristics of individual female anchovies (Engraulis anchoita) were studied by histochemical and ultrastructural techniques. Red, pink and white fibres were discerned on the basis of the activity of the metabolic enzymes succinic dehydrogenase, phosphorylase and myofibrilar ATPase, and the usage of Sudan and periodic-acid Schiff staining techniques. Red fibres were located at the surface, white fibres deep inside and pink fibres in between. The red fibres appeared flattened or ribbon-shaped in transverse section and they were located in rows separated by myosepta of connective tissue. The red and pink fibres were multi-innervated whereas the white fibres were terminally innervated. The relative proportion of the red muscle increased toward the caudal region, the white muscle diminished toward that region, whereas the proportion of pink muscle did not vary according to region, being scarce throughout. The distribution of capillaries was also investigated, and as a result, the vascular supply proved to be scarce in both white and pink muscle.