The Postembryonic Development of the Chondrocranium in the Nile Fish Sarotherodon galilaeus Linnaeus (Teleostei: Cichlidae) II. The Postbuccal Stages PDF

Keywords

zoology, fish, cartilage

Abstract

The development of the chondrocranium of two post buccal stages of Sarotherodon galilaeus (= Tilapia galilaea) (9 mm and 12 mm total length; 11 and 14 days old after fertilization, respectively) is described and compared with that of other bony fishes. In the 9 mm stage, absorption of cartilage is observed at the level of the fenestra hypophysea and becomes more pronounced in the 12 mm stage, early as compared with that in other bony fishes. The disparity is probably due to differences in environmental conditions. The neurocranial pharyngobranchiad apophysis, characteristic of the cichlid neurocranium, is developed from stage 9mm onwards as a slight ventral projection of the neurocranial base in the optic phase. The parachordal plates are connected posteriorly with each other by means of an epichordal commissure. The taenia tecti medialis originates as a posterior median extension of the epiphyseal cartilaginous bar. An interorbital septum is present. It consists anteriorly of cartilage and posteriorly of connective tissue membrane. A single, median, independant rostral cartilage is present dorsal to the ethmoid plate. The palatoquadrate cartilage articulates anteriorly with the neurocranium by means of an ethno palatine articulation; a rostropalatine articulation, however is absent.