Early ontogeny of the commercially valuable fish Piaractus brachypomus (Characiformes, Serrasalmidae) from the Amazon, Brazil

Abstract

The initial development of the red-bellied pacu Piaractus brachypomus is describedusing morphological, meristic and morphometric characteristics. A total of 127 individualswere analysed (47 in the yolk-sac, 35 in pre-flexion, five in flexion, 20 in post-flexion and20 in juvenile) with standard length varying between 2.92 and 48.61 mm. The larvae areborn poorly developed and have a discoidal yolk at6.33 mm standard length. Duringearly ontogeny, the mouth passes from terminal to subterminal and the anal openingreaches the vertical line over the midline region of the body. There are changes in bodyshape from long and moderate to deep, head length from small to large, and eye diame-ter from moderate to large. Dendritic chromatophores were present in the ventral, dorsaland upper part of the swim bladder in the early larval stages. Rounded spots are evidentall over the body in juveniles. The total number of myomeres ranges from 39 to41 (20–23 pre-anal, 17–20 post-anal). Through the morphometric relationships, it wasevidenced that the greatest changes during the initial ontogeny of P. brachypomus occurin the transition from the post-flexion stage to the juvenile period, indicating changes inbehaviour, foraging and physiology.