Ontogenetic Development of the Digestive Tract in Larvae of American Shad

Abstract

AbstractThe American Shad Alosa sapidissima was introduced into China for aquaculture in 2003. The histological characteristics of the digestive tract of American Shad larvae were examined from hatching to 33 d after hatching (DAH) with the aim of cultivating the larvae efficiently. The fertilized American Shad eggs were imported from Oregon and incubated in barrels with spring water maintained at 20.3–21.9°C in Qingyuan, Guangdong Province, China. The larvae were transferred to cement pools (water temperature at 24.0–25.0°C) at 13 DAH. Larvae were fed Artemia nauplii starting at 3 DAH, Artemia nauplii supplemented with gradually increasing proportions of commercial formulated feed after 18 DAH, and then only the formulated feed by 30 DAH. Based on the source of nutrition and structural changes in the digestive tract, larval development was divided into three stages: (1) lecitotrophic (0–2 DAH), (2) lecitoexotrophic (3 DAH), and (3) exotrophic (4–33 DAH). At 0 DAH of the lecitotrophic stage, the digestive system was undifferentiated and contained a large acidophilic yolk sac. By 1 DAH, the mouth and anus opened, the liver appeared, and the buccopharynx and intestine began to differentiate. The lecitoexotrophic stage began at the start of exogenous feeding, which led to the disappearance of the yolk sac. During the exotrophic stage, the esophagus could be differentiated into two different regions by 4 DAH. The intestinal tract developed quickly and differentiated into an obvious foregut and hindgut by 11 DAH. The primary stomach formed by 8 DAH and completely developed by 19 DAH with the presence of a few gastric glands. By 25 DAH, many gastric glands and a number of pyloric ceca were observed. The results of the study show the quick development of the digestive system in American Shad and we suggest initiating the weaning process at 23–25 DAH in the larvae.