DESCRIÇÃO MORFOLÓGICA DO DESENVOLVIMENTO INICIAL DE Brycon amazonicus (CHARACIFORMES, BRYCONIDAE) DO BAIXO AMAZONAS, PARÁ

The present study characterized the initial development of matrinxa Brycon amazonicus (Agassiz, 1829), as well as the changes in allometric growth patterns during the initial ontogeny of the species. A total of 260 laravae from induced reproduction were analyzed for morphometric and meristic variables, as well as the coeffient of allometric growth in relation to head and body length. The initial larvae (3.9 to 5.9 mm) of B. amazonicus are transparent and have a relatively large and elongated yolk sac. In the pre-flexion stage (5,9 to 7,6 mm) the larvae presented dendritic pigmentation in the upper region of the head and pointed along the upper region of the swimming bladder. At the flexion (8,3 to 13,5 mm) and post-flexion (15 to 26 mm), pigmentation intensifies with pigments (dendrict and punctiform) distributing mainly in the upper region of the head, lateral dorsum of the body and along the lateral line. Keywords:  Initial development; morphology; negative allometry; fish; matrinxa.