OSSIFICATION PATTERNS OF INTERMUSCULAR BONES IN DIFFERENT FISH SPECIES

Intermuscular bones, existing only in teleosts among advanced vertebrates, are segmental, serially homologous ossifications in the myosepta. However, there is limited information on the development and ossification of intermuscular bones. In the present study, the morphological development of intermuscular bone in rice eel (Monopterus albus) and weather loach (Misgurnus anguillicaudatus) was investigated using bone clearing and staining method. Study of these two species may imply the evolutionary ossification in teleost due to their different evolutionary status and different swimming modes. The results showed that in M. albus, a typical anguilliform swimmer and belonging to Synbranchidae of Synbgranchiformes, initial intermuscular bones (epicentrals) were ossified at anterior part at 30 days post hatching (dph) with the body length (BL) of 40 mm. Then intermuscular bones were ossified from the anterior to the posterior part. At 55 dph (BL 100 mm), all the intermuscular bones were basically appeared with all type " I” epicentral bones. However, in M. anguillicaudatus, carangiform swimmer and belonging to Cobitidae of Cypriniformes, initial intermuscular bones including epineurals and epipleural bones were ossified at posterior part at 27 dph (BL 17 mm). Then intermuscular bones were ossified from the posterior to the anterior part. At 40 dph (BL 35 mm), all the intermuscular bones were basically appeared with the types of " I”, " Y” and " 卜”. Moreover, through the use of osteoblast specific transcription factor (osterix) green fluorescent protein transgenic (osterix GFP) zebrafish (Danio rerio), the process of development and ossification of intermuscular bones were observed in vivo and the results showed that the intermuscular bones were ossified from the posterior to the anterior parts in D. rerio. The results from this study indicated that the ossification of intermuscular bones might be related to fish swimming mode, and their morphological polymorphism may be correlated with fish swimming mode and body type. However, whether the ossification of intermuscular bones has relation with fish phylogenetic evolution needs to be further explored.