| The dissertation primarily reviewed advances of studies on digestive physiology and nutrient requirement for marine fish larvae in recent years. Furthermore, a series of feeding experiments were conducted to investigate the digestive physiology, protein and methionine requirements for larvae of large yellow croaker.The microstructure and ultrastructure of stomach, intestine, liver and pancreas development, and pepsin activity in the larvae were studied. When water temperature was maintained at 24±1 ?C, the anterior tract of larvae bulged and formed presumptive stomach with a similar structure as oesophagus but no goblet cells since 4 days after hatching (DAH). At 13 DAH, the stomach bent at the posterior region, and began to differentiate into three different regions (cardiac, fundic and pyloric). Stomach mucous was formed and lined by a short simple columnar epithelium with irregular sparsely spaced microvilli, many apical mitochondria and rough endoplasmic reticulum. No gastric glands were observed until 21 DAH, grouped in acinar structures and distributed along the cardiac and fundic stomach mucosa, which were more numerous in the fundic stomach than in the cardiac region, but never observed in the pyloric region. Stomach had a Y-shaped, and its wall consisted of a mucosa, a submucosa, a circular muscle coats, and a serosa. Pigment granules were observed in connective tissues since 21 DAH, increasing in number as fish grew. No pepsin activity was detected until 25 DAH, which significantly increased up to 30 DAH, and decreased slightly thereafter. The presence of pepsin indicates the development of functional stomach and onset of acidic digestion, suggesting the weaning around 25 DAH should be considered.At hatching, the larvae possessed a primordial intestine as a straight tube laying dorsally to the yolk-sac, and lined by a simple columnar epithelium. At 3 DAH, the posterior region of intestine bent 90°, and a constriction of the mucosa that would...
|
PDF Full Text Request