Bone development in the jaw of Nile tilapia Oreochromis niloticus (Pisces: Cichlidae).

East African cichlids have evolved feeding apparatus morphologies adapted to their diverse feeding behaviors. The evolution of the oral jaw morphologies is accomplished by the diversity of bone formation during development. To further understand this evolutionary process, we examined the skeletal elements of the jaw and their temporal and sequential emergence, categorized by developmental stages, using the Nile tilapia Oreochromis niloticus as a model cichlid. We found that chondrogenesis started in Stage 17. The deposition of osteoid for the dermal bones commenced in Stage 18. The uptake of calcium dramatically shifted from the surface of larvae to the gills in Stage 20. The bone mineralization of the skeleton began in Stage 25. These data provide important information regarding the sequential events of craniofacial development in East African cichlids and lay the groundwork for studying the molecular mechanisms underlying adaptation of jaw structure to feeding behavior.