Studies on the fine structure of red and white fin muscles of the fish (Carassius auratus).

Abstract

The M. levator pinnae pectoralis of Carassius auratus appeared red and the M. levator pinnae lateralis abdominis pale to the naked eye. The fine structure of both these muscles were observed to correlate with the recent electrophysiological findings gained in the same material.The average diameter of both fibres was 36.0μ for the red fibres and 49.4μ for the white ones.The fibre type of both these muscles can be clearly identified by the examination of transverse sections. In the red fibres, the mitochondrial accumulation beneath the sarcolemma and rich deposits of glycogen were seen. The peripheral myofibrils of both tissues appeared in ribbon-like forms in a radial direction but almost all inner fibrils were polygonal in the red fibres.Regarding the arrangement of the myofilaments, no differences between the red and white fibres were observed. The Z, I, A, H and M bands were found to be well delineated. The Z lines were disposed to form a regular zigzag configuration and at the M lines well defined cross-bridges between the thick myofilaments were seen. The triads were located at the Z line level and the sarcoplasmic reticulum was well developed. In short, the internal structure of these two kinds of muscle was similar to that of the fast fibres of the frog.On the other hand, the innervation of both these muscles resembled that of the slow fibres of the frog; they showed the diffuse innervation. The nerve endings of both muscle fibres were so-called“en grappe”type. In the red fibres, densely grouped terminals in some areas of the fibre surface were found. The types of innervation might be classified as multi-focal diffuse innervation in the red fibre and mono-focal diffuse innervation in the white. These differences were confirmed by electrophysiological findings.The electrophysiological properties of the red fibres showed a tendency to be similar to the slow fibres of the frog and the white fibres to the fast fibres of the frog. However, the morphological differences between the fast and slow fibres in the frog could not be recognized in the muscles of this fish.