淡水石首鱼幼鱼外部形态与内部解剖学特征

External morphology and internal anatomical characters of juveniles of the freshwater drum Aplodinotus grunniens

世界上275种石首鱼类中仅有极少数终生生活在淡水中,北美洲特有的淡水石首鱼(Aplodinotus grunniens)是其中一种,其形态学和内部解剖学特征研究对探讨石首鱼类的系统发育和进化具有重要价值。本研究较系统地对淡水石首鱼幼鱼的外部形态学可量可数性状进行测量,对内部主要器官结构及矢耳石特征进行解剖学观察。结果显示:除了吻端、颐部和峡部外,淡水石首鱼体被两种鳞片,头部两侧的鳃盖及眼睛周边覆盖小圆鳞,头后身体包括喉部均被栉鳞,且在头背交界处存在两种鳞片的过渡类型;侧线鳞从头后一直延伸至尾鳍的1/2处。腹鳍第一鳍条膜稍延长形成特有的鳍丝。黏液孔主要分布在颐部,为五孔型;具有犬牙状的颌齿和咽齿,所有齿尖均向口腔内部方向弯曲,上咽齿盘分为左右对称的2个咽齿盘,而下咽齿盘愈合为一体;消化道主要由口咽腔、较短的食道、卜形胃、具有2个弯转的肠道及肛门组成,在胃与肠交界处具有7个环状排列的指状幽门盲囊。矢耳石的形态特征与中国的黄唇鱼相似。基于外部形态学和内部解剖学特征,讨论分析了淡水石首鱼与中国石首鱼物种的亲缘关系。淡水石首鱼归属于低级底栖肉食性鱼类,这与其特定的生态习性和摄食特性等相符合。本研究旨在为中国淡水石首鱼人工驯养和紫黑翼蚌的规模化寄生繁育奠定基础,也为探讨石首鱼类在海淡水区域地理格局演化提供了基础资料。

Only a few of the world’s 275 species of Sciaenidae live in fresh water throughout their life; one of which, is the freshwater drum Aplodinotus grunniens that is wildly distributed in North American. The study of its morphological and internal anatomical characters have great value to the phylogeny and evolution of Sciaenidae. In present study, the external morphological characters of the juvenile freshwater drum were systematically measured, and the anatomical structure of the main internal organs and sagittae otoliths were observed. The results indicated that there were two kinds of scales covering the body of the freshwater drum, except for the front of the snout, chin, and isthmus. Small cycloid scales were found on its operculum and around the eyes on both sides of the head, and ctenoid scales covered the body including the posterior head and jugular. The lateral line scales extended from the back of the head to half of the caudal fin. Some transition types of cycloid and ctenoid scales existed at the junction of the head and the dorsum. The first membrane of the ventral fin extended slightly to form a specific fin-silk. The juvenile freshwater drum had canine-like jaw teeth and pharyngeal teeth with different sizes, but all bent in an inward internal direction of the pharyngo-oral cavity. The upper pharyngeal disc was divided into two symmetrical parts, whereas the lower pharyngeal disc was fused into one. There were only five mental pores symmetrically distributed on the chin, which were Sciaena-form. The digestive tract consisted mainly of the pharyngo-oral cavity, a short esophagus, a divination-type stomach, the intestine with two bend, and the anus. There were seven circular digital pyloric caecas existing at the junction of the stomach and the intestine. The morphological characteristics of the sagittal otoliths of freshwater drum were similar to those of Bahaba flavolabiata. Based on the external morphology and internal anatomical characteristics, the freshwater drum has a closer evolutionary relationship with the Sciaena and should belong to low-grade benthic carnivorous fish, which consisted with its specific ecological habits and food consumption characteristics. This study not only provided an important foundation for the artificial domestication of freshwater drum and the large-scale parasitic breeding of pink heelsplitters in China, but also provided the basic material for the study of the evolution of the geographical evolution pattern of Sciaenidae in marine and freshwater regions.