New Aspects of Muscle Development in Fish

Our research within the FWF project P14193-B03 examines the patterns and mechanisms of muscle formation in embryonic and very young fish. We have followed muscle precursor cells (`stem` cells) and their products through their development to understand better which regula-tory genes and other factors make them grow into muscle fibres and at which point in time during the developmental sequence. Going one stage further, we have also been interested in which type of muscle fibre these precursor cells develop into (fish have at least 4 types of muscle fibres, each with different properties involved in the different functions the muscle may have within the animal). We used various methods, from electron microscopy and digital planimetry to molecular biology techniques to examine different carp species and a variety of other fish which are of considerable economic interest (trouts, sturgeons and tunas). We have shown that the previously accepted pattern of muscle development, based almost solely on the zebrafish (a small tropical species often found in different bred forms in house-hold aquaria) is valid, with modifications, for a wide range of fish including primitive (sturge-ons) and more advanced evolutionary forms. The origins and development of one particular type of muscle fibre, called tonic fibres, were previously uncertain, so these were examined in detail within the project. We found that these fibres develop from their own set of precursor cells and appear just at the time when the young fish begin to swim free and to hunt for their own food. Tonic muscle is thus probably prerequisite for efficient locomotory control during prey capture, shoaling and predator avoidance. A further, more general result of our work is that we found that nerves may play an essential role in directing the ultimate fate of the muscle precursor cells. By examining growth mechanisms from precursor cell activation on- wards, we have also been able to show that muscle development is strongly affected by temperature; not only cold or warm, but also by rising temperatures that mimic the natural conditions of a temperate river or lake during spring and summer. The latter result is new, and the developmental differences found also have a direct effect on fish flesh quality for human consumption, so are of considerable importance to the fish farming industry. Many of the variety of techniques we have perfected during our fish muscle research must be considered equally applicable in other fields of precursor cell and stem cell work including human and veterinary medicine.