Ontogeny of the digestive system and enzymatic activities in redtail botia Yasuhikotakia modesta larvae: A new fish species for freshwater aquaculture

The ontogeny of digestive functions of redtail botia Yasuhikotakia modesta was investigated 1–30 days after hatching (DAH) using morphological, histological, and digestive enzyme approaches. One-day-old larvae were nursed in a 15 m² rearing tank containing diverse natural food organisms. The water temperature during the rearing period was 27.7–31.0 °C. Morphological changes in the digestive tract showed that total body length increased from 2.94 ± 0.13 mm to 22.25 ± 3.33 mm, along with relative gut length (RGL) ranged from 0.39 to 0.74, and mouth size increased from 0.21 ± 0.04 mm to 1.87 ± 0.16 mm. The redtail botia larvae started exogenous feeding at 3 DAH (4.13 ± 0.39 mm), and yolk sac absorption occurred between 3–5 DAH (4.13 ± 0.39–4.36 ± 0.17 mm). By 6 DAH (4.61 ± 0.24 mm), the digestive tract differentiated into the oral cavity, esophagus, stomach region, and intestine. The stomach appeared on 7 DAH (4.77 ± 0.28 mm) and gastric glands were identified on 12 DAH (9.79 ± 1.04 mm), indicating a fully functional stomach. By 15 DAH (11.42 ± 0.97 mm), the digestive tract completed its morphological structures with the appearance of the pyloric sphincter, a constriction of the mucosa between the stomach and the intestine. Digestive enzyme analysis detected trypsin, chymotrypsin, and amylase from 1 DAH (2.94 ± 0.13 mm), while pepsin was first detected at 12 DAH (9.79 ± 1.04 mm), coinciding with gastric gland formation. These findings provide information to develop efficient larval feeding strategies in this species. • Study digestive system and enzyme activity in redtail botia larvae (days 1–30). • Exogenous feeding began on day 3 and the digestive tract fully formed on day 15. • Trypsin, chymotrypsin, and amylase detected at hatch while pepsin detected on day 12. • Provide information to develop efficient larval feeding strategies.