COMPARATIVE ANATOMY AND SYSTEMATICS OF THE TUNAS, 



GENUS THUNNUS ■ 



By Robert H. Gibbs, Jr. and Bruce B. Collette Systematic Zoologists (Fishes) 



Division of Fishes, U.S. National Museum, Washington, D.C. 



AND Bureau of Commercial Fisheries Ichthyological Laboratory, 



U.S. National Museum, Washington, D.C. 20560 



ABSTRACT 



The taxonomic status of the tunas of the world, often 

 placed in the genera Thunnus, Germo, Neothunnus, 

 Parathunnus, and Kishinoella, is assessed through the 

 use of external morphological and internal anatomical 

 characters. Seven species, all included in the single 

 genus Thunnus, are considered valid: T. thynnus, the 

 bluefin tuna; T. alalunga, the albacore; T. obesus, the 

 bigeye tuna; and T. albacares, the yellowfin tuna, are 

 circumglobal in distribution; T. atlanticus, the blackfin 

 tuna, and T. tongsol, the longtail tuna, are restricted 

 to the western Atlantic and the Indo-West Pacific, 

 respectively; T. maccoyii, the southern bluefin tuna, 

 is known in the southern Pacific and Indian oceans and 



off northwestern Australia. Two subspecies of T. thyn- 

 nus are recognized: T. t. thynnus in the Atlantic and 

 T. t. orientalis in the Pacific. 



In Part 1 the comparative anatomy is described and 

 characters are given for differentiating the species by 

 means of counts and measurements and by comparison 

 of the skeletal, visceral, and vascular systems. In 

 Part 2 the genus Thunnus is characterized with respect 

 to other genera of Scombridae, and for each species a 

 synonymy, a resume of distinctive characters, discus- 

 sion of type specimens and nomenclatural problems, 

 and a review of known geographic distribution are given. 



The purpose of this paper is to demonstrate that 

 there are, at most, seven species of tunas in the 

 world, and that they should be placed in the single 

 genus Thunnus which is circumglobal in distribution 

 and constitutes one of the most important groups of 

 commercial fishes. Much time and money have 

 been expended in gathering meristic, morphometric, 

 anatomical, distributional, and life-history data, yet 

 the systematic and nomenclatural status of the group 

 remains unsatisfactory. Over the years, 10 generic 

 names and 37 specific names have been applied to 

 the seven species which we recognize. The confu- 

 sion is due, at least in part, to the pelagic habits of all 

 of the species and to their large adult size, which 

 makes specimens difficult to preserve and store and 



Note. — Approved for publication April 18, 1966. 



' Research supported in part by National Science Foundation Grant 

 No. 2102 to Woods Hole Oceanographic Institution (1956-1958) and by 

 U.S. Fish and Wildlife Service Grant No. G 48 to Boston University (1962). 



recjuires that observations be made at the time of 

 collection, often under adverse conditions. Study 

 material over the great size range is not easily 

 obtained, so that growth changes are hard to evalu- 

 ate. The economic importance of the group has 

 led many biologists to dabble in tuna taxonomy, 

 using variable characters and different means of 

 counting and measuring. Provincialism has caused 

 otherwise competent workers to believe that the 

 kinds of tunas in their home areas are unique and to 

 cling tenaciously to locally established names despite 

 contrary evidence. 



Our studies have been built upon the work of a 

 number of previous investigators. We have come 

 to realize, as many of these workers have, the great 

 value of internal anatomical characters as a means of 

 distinguishing tuna species. In this field, Kishinouye 

 (1915, 1917, 1923) pioneered. The most extensive 



FISHERY bulletin: VOL. 66, NO.l 



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