Morphology of the digestive tract and the expression of the proteolytic enzyme and peptide transporter genes in the larvae of the tambaqui, Colossoma macropomum

Abstract The initial development of the digestive system and the expression of the genes that codify the proteolytic enzymes – pepsin and trypsin – and the peptide transporter – pept1 – were investigated in the larvae of the tambaqui, Colossoma macropomum . The larvae were raised in recirculating aquaculture system (27.99 ± 0.05°C) until 36 Days After Hatching (DAH), being then fed on Artemia nauplii up to 21 DAH, when pelleted feed (55% crude protein) was introduced. The weight and total length of the C. macropomum larvae were conferred at 6, 9, 12, 15, 18, 21, 26, 31 and 36 DAH, when samples of whole larvae were also obtained for histological analysis and the determination of gene expression. Initially, the digestive tract of the larvae was a straight tube, with the first intestinal loop and epithelial folds being formed between 15 (11.06 ± 0.50 mg, 9.91 ± 0.11 mm) and 18 DAH (27.03 ± 1.76 mg, 11.36 ± 0.20 mm). The development of the pyloric caeca was identified from 21 DAH (56.03 ± 3.00 mg, 14.07 ± 0.23 mm) onwards. The gastric glands were observed initially at 12 DAH (4.17 ± 0.20 mg, 7.89 ± 0.12 mm) and the pyloric region was clearly identifiable at 21 DAH (56.03 ± 3.00 mg, 14.07 ± 0.23 mm). The expression of the pepsin and pept1 genes was detected at 12 DAH (4.17 ± 0.20 mg, 7.89 ± 0.12 mm), while the trypsin gene was detected from 21 DAH (56.03 ± 3.00 mg, 14.07 ± 0.23 mm) onwards. These findings demonstrate ontogenetic synchrony between morphological and functional maturation of the digestive tract, with C. macropomum larvae showing increased digestive capacity around 21 DAH.