四指马鲅(Eleutheronema tetradactylum)消化系统胚后发育组织学观察

Histological Observation of the Post-Embryonic Development of Digestive Tract of Eleutheronema tetradactylum

关键词:  四指马鲅  消化系统  胚后发育

Key words:  Eleutheronema tetradactylum  Digestive system  Post-embryonic development

摘要:

运用组织学切片技术研究四指马鲅(Eleutheronema tetradactylum)出膜后1–30 d (Day after hatching, DAH)仔鱼的消化系统形态和结构的变化。结果显示，在温度29–32℃、盐度25–28、溶氧4.80–5.5 mg/L、pH 8.0–8.3条件下，1 DAH仔鱼消化管尚未分化，由紧贴腹壁和卵黄囊的肠管组成。卵黄囊在3 DAH时完全吸收完毕，仔鱼开口摄食，消化管也与外界相通，此后逐渐分化出食道、胃部和肠道，一定程度上能自主消化吸收食物维持自身生长，逐渐从内源性营养期过渡为外源性营养期。15 DAH时出现幽门盲囊和胃腺，消化道结构和功能成分进一步发育完善，消化能力显著提高，30 DAH仔鱼消化道具备与成体相似的结构和功能。肝脏和胰腺分别在2 DAH和5 DAH时分化，随着仔鱼的生长而快速发育，至30 DAH时具备与成体相似的结构和功能。四指马鲅消化系统的发育表现为结构与功能密切联系且逐渐发育成熟的特点。本研究根据四指马鲅消化系统的发育特点讨论了育苗过程中的三大危险期并提出应对措施。

Abstract:

Eleutheronema tetradacty is a tropical inshore marine fish species that belongs to the Polynemidae family. It has very high commercial values. Previous studies mainly focused on the stock structure and taxonomy of this species. However, the information about morphology and structural and functional biology has been limited, especially little is known about the development of the digestive system. In this study we applied the histological method to investigate this issue of E. tetradactylum aged Day 1 to Day 30 after hatching (DAH 1 to 30). Thus we may develop a better feeding strategy during artificial seedling rearing and improve the survival rate of the larvae. The experimental conditions were temperature 29–32℃，salinity 25–28, dissolved oxygen 4.80–5.5 mg/L，and pH 8.0–8.3. We found that on DAH 1, the digestive tube was not differentiated, and was composed of intestinal tubes that were attached to the abdominal wall and the yolk sac. On DAH 3, the yolk sac was fully absorbed, the larvae began feeding, and the digestive tube started to communicate with the outside. This indicated a switch from the endogenous nutrition to the exogenous feeding, and from this point, the larvae could maintain the growth by relative independent digestion and absorption through the gradually differentiated esophagus, stomach and intestine. The gastric gland and pyloric caeca appeared on DAH 15, which greatly improved the digestion and were the signs of the juvenile stage. On DAH 30, the structure and function of the digestive tract were well developed, which resembled that of the adults. The liver and the pancreas started to differentiate on DAH 2 and DAH 5 respectively, and they developed fast as the larvae grew. These observations suggested that the development of the digestive system was highly associated with the functions. Based on the characteristics of the digestive system, we further discussed issues in three major critical stages in the process of seedling rearing and proposed solutions for each stage.