三疣梭子蟹和华溪蟹主要器官比较组织学的初步研究

A preliminary study of comparative histology of major organs from Portunus trituberculatus and Sinopotamon

近年来随着养殖业的发展,蟹类病害频繁发生,日趋严重。在开展病害研究过程中,由于三疣梭子蟹Portunus trituberculatus的SPF(无特定病原体)材料难于获得,而试验蟹的获得又受到养殖条件、养殖周期等因素的限制,因此阻碍了相关研究的开展,尤其是病毒学研究的进展。筛选一种可替代的模式生物,并开展相关研究显得尤为迫切。华溪蟹Sinopotamon和三疣梭子蟹亲缘关系较近,作为野生的蟹类容易获得,价格低廉,也容易在实验室条件下饲养。笔者在梭子蟹病原研究中发现,华溪蟹不带梭子蟹病原,但在实验条件下可感染相关病原,是开展此两类蟹病原体研究的较好实验动物,有必要开展这两种蟹的组织比较形态学的基础研究,以支持相关的应用研究。笔者经过对三疣梭子蟹和华溪蟹的组织石蜡切片观察发现,两种蟹的各组织器官结构基本相似,各组织结构都由4层构成,即粘膜层、粘膜下层、肌层和外膜。上皮细胞分泌物形成几丁质板,覆盖在上皮细胞表面。三疣梭子蟹的食管粘膜下层较发达。华溪蟹食管粘膜下层的肌层均相对较薄,食管腔较小。这两种蟹的胃壁结构无明显差别。在三疣梭子蟹的局部胃壁,可见嗜酸性几丁质层,上皮细胞顶部间有间隙,间隙中有一些嗜碱性物质。三疣梭子蟹肠粘膜下层不明显。华溪蟹的中肠非常细小,被肝胰腺等组织包裹,难以分离,管腔小,管壁外结缔组织少。两种蟹肝胰腺均由许多分枝的肝小管组成,小管间为结缔组织,血窦。肝小管由单层柱状上皮构成,高低不等,可以明显区分出分泌细胞、吸收细胞、储存细胞和胚性细胞4种形态的细胞,其功能也不同。三疣梭子蟹鳃轴基本弯曲,窄处鳃轴与鳃丝粗细相当,鳃丝和鳃小片间隔较大。华溪蟹鳃轴笔直延伸,窄处鳃轴明显粗于鳃丝,鳃丝间隔较小。两者鳃小片均由扁平上皮组成,外侧有薄层几丁质板。华溪蟹的鳃血管中可以明显看到较多染成红色的血细胞。三疣梭子蟹心肌纤维排列松散,线粒体较少,形态多样。华溪蟹心肌纤维排列致密,线粒体多呈群分布,且数量更多。心肌由梭形心肌细胞组成,有横纹,彼此相连成网,其周围有少量原生质。肌细胞的核呈棒状。

The swimming crab Portunus trituberculatus is one of the favorite sea foods for its delicious,tender and nutritious meat in the coastal areas.Because of small investment and big return,the aquaculture of the crab has been thriving along the coast.However,severe diseases occur frequently in recent years.Studies on the disease diagnosis and control has been undertaken,anyhow,but the difficulties to find SPF crabs which is restricted by the condition of the crab＇s life cycle and culture conditions hinder the advancement of the research work,especially in the field of virology.It is urgent to screen an alternative model crab and carry out related research work.P.trituberculatus is close to Sinopotamon in genetic relationship.Wild Sinopotamon could be easily captured,conveniently cultured in laboratory,and is of low price.It was observed in previous research work that wild Sinopotamon did not carry pathogen of P.trituberculatus,but could be infected by the latter＇s pathogens under experimental conditions.So it may be an ideal experimental animal for studying the disease diagnosis and control of both crabs.It is necessary to carry out comparative histology study of the two crabs to support related application research work.In this paper,paraffin sections of major organs of the two crabs were prepared,and the tissue structure was observed and their similarity was found.These tissues all consisted of four layers： mucous layer（simple columnar epithlium）,submucosa,tunica muscularis and adventitia.Chitinous sheet formed by epithelial cell secretion covered the skin.Esophageal submucosa of P.trituberculatus was more developed than that of Sinopotamon.And the muscle layer of the latter was thinner and the esophageal cavity smaller.The structure of gastric wall of the two crabs showed no significant difference.In P.trituberculatus,eosinophilic chitin layer was observed in partial of gastric wall;and at the top of epithelial cell,interspace containing basophilic material was found;intestinal submucosa of the crab was not distinct.The midgut of Sinopotamon was very small,wrapped with hepatopancreas tissue,and was rather difficult to be separated.The lumina were small with little connective tissue around the lumen wall.The hepatopancreas of the two crabs were built up with many branched hepatic ducts linked with connective tissue and sinusoids.Hepatic ducts were constituted by single-layer columnar epitheliums.Four types of cells with different functions,B-cells、R-cells、F-cells、E-cells could be clearly distinguished.Gill axis of P.trituberculatus was bent;the gill filament and gill axis were of same thickness.The interval between gill filament and branch leaves of P.trituberculatus was larger than that of Sinopotamon.Gill axis of Sinopotamon was almost straight.Gill filament was coarser than gill axis.The branch leaves were constituted by simple pavement epithelium cells.They were covered with thin chitinous sheets.Many erythrocytes were observed in blood vessels in the gills of Sinopotamon.The cardiac muscle fibers of P.trituberculatus were loosely arranged,with less quantity of mitochondria.As for Sinopotamon,the cardiac muscle fibers were compact,with more mitochondria,distributed in groups.The cardiac muscle was consisted of spindle cardiocytes,with transverse striation,and connected each other into a network.The nuclear of myocytes was rod-shaped.