The development of the digestive system in larvae of the Neotropical fish P. argenteus was analyzed histologically. On the 3 rd day after hatching, the digestive system comprised oropharyngeal cavity, esophagus and simple undifferentiated tube. Since secreting cells, positive to Alcian Blue (AB), were found in the esophagus, digestive activity in the initial phase had occurred. On the 18 and 28 th days after hatching, the esophagus was positive for AB and Periodic Acid Schiff (PAS) stain. The stomach was fully differentiated, with the cardiac, fundic and pyloric regions. Different regions of the epithelium were characterized by basic and acidic secreting cells (AB and PAS positive). On the 18 and 28 th days after hatching, the intestine was long, coiled and divided into proximal, middle and distal segments with pyloric ceca. Secreting cells in different regions of the gut were either positive or negative for AB and PAS. Results showed that larvae of P. argenteus exhibited digestive activity on the third day after hatching, with fully differentiated stomach and intestines on the 18 and 28 th days and their different regions featuring secreting cells.

Neste experimento, utilizaram-se cinco aquários cilíndricos com relevo no fundo (em forma de anel) e cinco retangulares com fundo liso para estudo da influência do formato do aquário na sobrevivência e no desenvolvimento de larvas de matrinxã Brycon cephalus. Observou-se melhor eficiência dos aquários retangulares, confirmada pela maior sobrevivência e biomassa. Os valores de temperatura, pH, condutividade e oxigênio dissolvido foram similares entre os tipos de aquários, sugerindo que esses parâmetros não influenciaram os resultados. O relevo no fundo dos aquários cilíndricos afetou negativamente o cultivo de larvas de matrinxã, pela criação de zonas com pequena capacidade da água em suspender partículas, o que resultou em acúmulo de dejetos, predadores, competidores e alimento. Aquários retangulares com fundo liso são mais adequados ao cultivo de larvas de matrinxã, por promover melhor circulação da água.

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