Ontogeny of the digestive tract of Brycon amazonicus (Teleostei, Bryconidae) under culture conditions: from hatching to juvenile stage.

In the present study, the morphological development of the Brycon amazonicus digestive tract is described to provide basic knowledge for nutritional studies and, therefore, increase the survival of this species during larviculture. Samples were collected from hatching up to 25 days of age, measured, processed and observed under a stereomicroscope and light microscopy. Newly hatched larvae presented their digestive tract as a straight tube, dorsal to the yolk sac, lined with a single layer of undifferentiated cells. At 24 h post-hatching (hPH), the buccopharyngeal cavity was open, but the posterior region of the digestive tube remained closed. At 25 hPH, the digestive tube was completely open and could be divided into buccopharyngeal cavity, oesophagus and intestine. At 35 hPH, the intestine presented a dilatation in the proximal region, which had the function of storing food. Differentiation of the stomach started at 83 hPH, and mucous cells were observed in the epithelium. These cells are important in the production of mucus, whose function is to protect the organ against acidity, although the gastric glands began developing only from 171 hPH, when three stomach regions were observed: cardiac, fundic and pyloric. The gastric glands were observed in the cardiac region, indicating that this organ already had digestive functionality. From 243 hPH, the absorption and assimilation of nutrients were already possible but, only from 412 hPH, the digestive tract was completely developed and functional.

Moments of induced spawning and embryonic development of Brycon amazonicus (Teleostei, Characidae).

Based on the economic and ecological relevance of Brycon amazonicus, the goal of this work was to describe the diameter of oocytes and eggs of this species, as well as the chronological embryonic development. The material was provided by Buriti fish farm, Nova Mutum - MT, Brazil. Samples of both oocytes and eggs were obtained from extrusion to hatching. The material was fixed and measured under stereomicroscope, and the samples were divided for light microscopy or scanning electron microscopy (SEM) analyses. At extrusion, the oocytes were bluish green. The frequency distribution of oocytes revealed that 87.7% of them ranged from 1.11-1.30 mm in diameter. During incubation, the total diameter of the eggs increased from 1.22 ± 0.04 mm to 3.06 ± 0.46 mm in the first 60 min post fertilization (PF), and growth ceased at 180 min PF. Between 10-30 s PF, most eggs were fertilized and fertilization cones were observed from 10 s onwards after gamete activation. The main fertilization events took place asynchronically and spermatozoa were visualized in the micropyle vestibule up to 90 s PF. The first cell was formed in the centre of the blastodisc 20 min PF. The morula stage was identified 2 h PF and, 3 h later, 70% of the yolk was covered by the blastoderm; the blastopore was almost entirely closed at 6 h PF. The cephalic and caudal regions of the embryo could be defined 8 h PF and hatching occurred after 13 h of embryonic development. The larvae hatched with undifferentiated organic systems and with a large yolk sac, free from swimming abilities or visual acuity.