Ontogenetic development of the digestive system in yellowtail kingfish Seriola lalandi larvae

Ontogenetic development of the digestive tract and associated organs in yellowtail kingfish (Seriola lalandi, Family: Carangidae) larvae was morphologically and histologically examined using light microscopy from hatching to 36 days after hatch (DAH). The first developmental phase started from hatching when the digestive tract was a simple tube and ended with the onset of exogenous feeding. The second developmental phase was from the start of exogenous feeding to the appearance of gastric glands, in which eosinophilic supranuclear vacuoles occurred in the hindgut on 4 DAH and lipid vacuoles occurred in the anterior midgut on 5 DAH, indicating the start of protein and lipid absorption. After the stomach formation on 5 DAH, the digestive tract was distinctively divided into buccopharyngeal cavity, oesophagus, stomach, midgut and hindgut. Following the intestinal curve on 8 DAH, goblet cells, pharyngeal teeth, taste buds and the tongue also appeared. The third developmental phase started from the appearance of gastric glands on 15 DAH and continued onward. The stomach was divided into cardiac, fundic and pyloric regions when the pyloric caeca formed on 18 DAH. Gastric glands distributed in cardiac and fundic regions, but not in the pyloric region. The formation of the fundic stomach signalled the starting point of weaning. This study shows the quick development of the digestive system in yellowtail kingfish, and the results should lead to a better understanding of the ontogeny of fast-growing fish larvae and improvement of larval rearing success in hatcheries.