PATTERNS OF SUPERFICIAL FIBER FORMATION IN THE EUROPEAN PEARLFISH (RUTILUS-FRISII-MEIDINGERI) PROVIDE A GENERAL TEMPLATE FOR SLOW MUSCLE DEVELOPMENT IN TELEOST FISH

The debate about the pattern of muscle formation in teleost fish has r ecently been heightened in the literature. Here we examine superficial muscle development in the pearlfish, a cyprinid endemic to a small ar ea of Central Europe, and uninfluenced by economic interest and breedi ng. Using light and electron microscopy, histochemistry and immunohist ochemistry techniques, we report that: (1) Superficial fibre precursor s originate close to the notochord, are part of the same cell populati on as the so-called muscle pioneer cells, and are transferred laterall y to end up at the surface of the myotome. (2) Superficial fibre matur ation is exceptionally rapid. Structural and enzymatic functionality i s attained at a time when prospective deep fibres have not passed beyo nd the early myotube state. This strong contrast weakens as the embryo develops. (3) Apart from the muscle pioneers, the superficial fibres appear to be capable of functioning before they receive any direct inn ervation, implying that signals are transferred to these fibres via ce ll-to-cell junctions. We suggest that the capability of rapid superfic ial fibre maturation is a rather general feature among teleosts and ma y aid pre-hatch survival under a variable environment. Our results ind icate that muscle formation in teleost fish may follow a common basic pattern that is open to considerable ontogenetic and phylogenetic modi fication in response to habitat conditions.