Golgi stain identifies three types of fibres in fish muscle.

Using Golgi infiltration we have studied the structure and disposition of transverse tubules in muscle fibres from the sand dab fin musculature. Three types of fibres differ significantly from each other in the extent and disposition of junctions between transverse tubules and the sarcoplasmic reticulum. These correlate with the three groups of fibres having different relaxation times shown in the accompanying paper (Gilly & Aladjem, 1987). Fibres with very slow relaxation (tonic fibres) correspond to those which have an unusual disposition of T tubules and very rare T-SR junctions. In the fast twitch fibres the peripheral T tubules segments converge into tangentially arranged tubules before joining the plasmalemma.