军曹鱼仔稚鱼脊柱和附肢骨骼的发育特征

Development characteristics of the vertebral column and the appendicular skeleton in larval and juvenile cobia(Rachycentron canadum)

为探明军曹鱼仔稚鱼早期脊柱及附肢骨骼的发育特征,本研究采用软骨-硬骨双染色技术,分别利用阿利新兰、茜素红对软骨、硬骨以及1~33日龄军曹鱼仔稚鱼全骨骼进行染色,系统观察并描述其脊柱和附肢骨骼的发育特征。结果显示,军曹鱼脊柱开始发育的标志为7日龄仔鱼中脉弓和神经弓的出现;13日龄稚鱼椎骨、神经弓和脉弓开始骨化;背肋、腹肋分别于17、20日龄开始骨化;29日龄稚鱼脊柱骨化完成。附肢骨骼骨化起始顺序依次为胸鳍、尾鳍、腹鳍、背鳍和臀鳍。胸鳍匙骨于4日龄出现,肩胛骨孔于12日龄出现,同时上匙骨开始骨化;乌喙骨与肩胛骨于20日龄开始骨化;第1尾下骨于5日龄出现,15日龄稚鱼尾杆骨、侧尾下骨和尾鳍鳍条开始骨化,18日龄稚鱼尾下骨开始骨化;腹鳍支鳍骨于17日龄延伸至匙骨,同时腹鳍开始骨化;臀鳍和背鳍于17日龄由前向后开始骨化。研究表明,军曹鱼在13日龄进入稚鱼期,早期发育阶段的骨骼发育特征与其功能性适应密切相关。本研究结果对研究军曹鱼早期骨骼发育与功能适应、优化养殖条件有重要作用。

Cobia(Rachycentron canadum)is an increasingly important marine fish with significant potential for aquaculture in China.Several studies have shown that this fish exhibits distinct locomotion patterns,feeding behaviors and nutritional demands during the larvae and juvenile stages.In order to explore the developmental characteristics of the spine and appendage bones in the early stages of cobia,this paper described the morphologic ossification characteristics of the vertebrae and appendages of larval and juvenile cobia[1 to 33 days post hatching(dph)]using a cartilage bone clearing and staining technique to obtain information on the structural development and functional adaptation of larvae and juveniles organs.After cartilage and bone were stained with alcian blue and alizarin red,vertebral columns were observed to develop from haemal arches and neural arches at 7 dph.Then,the centrum,haemal arches,and neural arches began to ossify at 13 dph.The dorsal rib and ventral rib began to ossify at 17 and 20 dph,respectively,and the vertebrae were fully ossified at 29 dph.The appendicular skeleton developed in the following order:the pectoral fin is the first to develop,followed by the caudal,ventral,dorsal,and anal fins.The pectoral fin began to develop from the cleithrum at 4 dph.The supracleithrum of the pectoral fin ossified at 12 dph and at the same time,the scapula foramen appeared,while the coracoid and scapula began to ossify at 20 dph.The hypural 1 of the caudal fin appeared at 15 dph,the urostyle,parhypural,and fin ray began to ossify at 15 dph,whereas the hypural began to ossify at 18 dph.The ventral fin plate extended to the cleithrum at 17 dph and simultaneously,the ventral fin began to ossify.At 17 and 18 dph,the dorsal and anal fins were ossified in the same pattern.The appendicular skeleton,with the exception of the urostyle,cleithrum,and pelvic girdle,underwent cartilaginous ossification.The development of the vertebral column and appendicular skeleton,on the other hand,is accompanied by changes in feeding patterns and locomotion patterns,such as the emergence of pectoral fin primordia that created conditions for the beginning of larval movement,the development of tail fin folds that enhanced its swimming ability,and the development of pectoral and tail fins in furtherance of cobia’s quick swimming.The results of the study show that exercise skeletons were preferentially developed,such as ossification of the vertebral column and the appendicular skeleton,which enhanced cobia’s forced swimming ability.In addition,hypural healing has been found during skeletal development.In accordance with this process,this paper considered that the morphotype transition of the caudal fin is associated with hypural healing.It is suggested that the osteological ontogenesis of larval and juvenile cobia is closely related to changes in their movement patterns.At 22 dph,scale outgrowth could be found on the caudal peduncle,the vertebral column and appendicular skeleton tended to be fully ossified,and the body features of the fish are the same as adult fish except for the shape of the caudal fin.This study proposes the use of the start of vertebrae ossification as a criterion to distinguish between larval and juvenile cobia,which are considered to enter the juvenile stage at 13 dph.The results suggest that the early bone developmental characteristics of cobia larvae and juveniles are closely related to their functional adaptation.Research on the development of the vertebral column and the appendicular skeleton of cobia is important to enhance the understanding of environmental preferences and functional morphology.