Développment post-embryonnnaire du squelette céphalique en relation avec les changements morphologiques externes chez labeo parvus (Ostariophysi, Cyprinidae)

Postembryonic development of the cephalic skeleton in relation to external morphological changes in Labeo parvus (Ostariophysi, Cyprinidae) Postemoryonic development ot the external morphology and the cephalic skeleton in Labeo parvus has been studied from hatching up to 29 days post-hatching. The specimens were obtained from a single artificial reproduction achieved in October 2007 at the fish farming station of the Laboratory of Hydrobiology and Aquaculture (LHA) of the University of Abomey-Calavi (UAC) in Benin. After being trypsin-fixed, larvae and fry were cleared and stained with Alcian blue and alizarin Red S. Study of the external morphology revealed that average growth of L. parvus is 1.7 mm per day from hatching to 29 days post-hatching. The mouth opens at 18 h and the yolk sac is completely reduced at 36 h. At hatching, the larva does not show any cartilaginous structure. At 18 h, the trabeculae, the parachordales plates, the wall of otic capsules, Meckel's cartilages, the hyosymplectics, the ceratohyals and the three first ceratobranchials are visible. At 24 h, the fourth and the fifth ceratobranchials are formed. At 36 h, the otic capsules, the taeniae marginales, the ethmoid plate, the palatoquadrates, the hypohyals, the basibranchials, the four first pairs of hypobranchials and the scapular girdle are already in place. Between 36 h and 4 days, the chondrocranium grows. The Suspensorium is already articulating with the neurocranium and the hyoid bar is suspended to the hyosymplectic. At 10 days, all the important structures are formed and the chondrocranium regresses. The first bony structures, i.e. the operculars, the jaws and the pharyngeal teeth appear at 4 days. The opercular is well developed at 6 days and the larva is already able to create a water current from front to back. At 8 days, the mandible, the premaxillaries and the maxillaries as well as a pair of branchiostegal rays appears. At 10 days, the parasphenoid and the basioccipital appear to form the floor of the braincase and preventing any impact of intaken exogenous food on the base of the brain. From 14 to 29 days, new bony structures appear and render the braincase more efficient.