The larval and juvenile 6tages of the Plecostei 



The Plecostei, that if t -a tunas and bonitos, differ greatly in their structure 

 from- the Teleostomi. They occupy the highest position among the fishes, and their 

 flesh is similar to that of the higher vertebrates. Furthermore these fishes are 

 important economically and their fisheries are expected to expand greatly in the 

 future. Therefore the investigation of the embryology and development of these 

 fishes is necessary from the point of view of both science and industry. It appears 

 that all of these fishes hatch in pelagic waters and even the larval and juvenile 

 specimens are unfortunately not easy to come by . This , past summer I announced 

 through the local government offices and fisheries experiment stations, which have 

 the greatest opportunity to obtain these juvenile fish, that I would pay from one 

 to five yen apiece for specimens under 3 06 inches in length which fishermen might 

 send to the Agriculture Department of the University. As a result I was informed 

 that there were prospects of getting such material from the Okinawa Prefecture 

 Fisheries School, and the Yashakumon dried skipjack stick factory of the Taiwan 

 Fisheries Company at Keelung kindly sent me 4.3-inch and 7.2-inch specimens of 

 Buthynnns yalto which were taken in August and September in the sardine set nets at 

 the mouth of Keelung Harbor. Mr. Yokoya was sent to the Benin Is. by the University 

 to test a large surface trawl with the object of collecting Juveniles, and although 

 this experiment has not yet been completely successful, with such attention being 

 given to the problem in all areas I trust that it will not be long before suitable 

 material can be obtained. 



As a basis on which to conduct the searoh for Juvenile Plecostei I wish to 

 summarise here the past knowlsdge concerning them. In 1330 the Danish scholar 

 Lutken published a work on the marine fishes of the Atlantic in which he recorded 

 one specimen about .72 inch long which was found in surface trawl collections made 

 by the "Galatheas" June 3, 134.6. He identified it as probably being an albacore, 

 and gave the same identification for a number of even smaller specimens about .36 

 inch long which resembled it. He published figures of the large specimen and one 

 of the small ones. This is perhaps the earliest published record of juvenile 

 Plecostei. (Figures 1 and 2). 



Later Gunther studied the collections made by the "Challenger" and in his re- 

 port published in 1839 he recorded juvenile specimens about .72 inch long which 

 were taken by surface trawl between Japan and the Admiralty Is. (south of the 

 Carolines) between March and April, 1375. He identified these as being probably 

 Euthynnus vaito and published a figure of one of them. (Figure 3). 



Lutken Identified his specimens as tunas solely because he thought that they 

 resembled tunas in outward appearance, and unfortunately there is no conclusive 

 evidence sufficient to guarantee the correctness of this identification. In both of 

 Lutken' s Juveniles the first two spines of the dorsal are short and the third spine 

 is the longest. The first dorsal, with the exception of a small portion at its 

 posterior end, is black, the mouth is wide, the teeth are sharp, and the posterior 

 end of the maxillary extends as far as the center of the eye. According to Gunther 

 the coloration of the fins as shown In the figures makes it more likely that these 

 specimens are oybiids. I think, on the basis of the shortness of the anterior 

 spines, that they are not tunas nor bonitos. Furthermore, the curves on the sur- 

 faces of the myotomes are simple and their angles are obtuse, which makes me t hink 

 that they are probably not cybiids either. 



The Juvenile which Gunther considered to be a Euthynnus yaito . according to 

 the figure, can be deemed to be a plecostean fish since the first spine is the 

 longest of the first dorsal, the caudal peduncle is flat, and there are keels on 

 both sides of it, however, the whole body is said to be covered with fine scales 

 and consequently It cannot bo a katsuwonid. It may perhaps be a juvenile thunnld. 



