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Fish Bulletin No. 97. A Descriptive Study of Certain Tuna-like Fishes

Abstract

This project was undertaken in response to an inquiry concerning the relationship of certain species to the tunas. While the original intent was merely to supply a sound biological basis for a definition of the term "tuna", the ultimate scope of the work and the content of this report covers a relatively complete description of the numerous species investigated.

In order to have a factual basis upon which to evaluate relationships, the present report includes a description of two species of Sarda and of the Pacific mackerel, Pneumatophorus diego, representing, respectively, Kishinouye's families Cybiidae and Scombridae. While this admittedly affords an insufficient foundation upon which to build a solid structure of classification, it suffices to appraise the validity of Kishinouye's order Plecostei.

The writer's interest lies primarily in a separation of the valid species of the Thunnidae and Katsuwonidae and a description of each that will enable a positive identification of any individual. It is his contention that if a specimen cannot be unequivocably assigned by any worker to a given species, then the definition of that species is at fault. The creation of questionable specific and subspecific groups into which an individual must be arbitrarily placed in disregard of other characters is disconcerting and creates the confusion to which every worker in this field alludes. The confusion is in the literature and not in nature. Thus Euthynnus lineatus and E. yaito are classified by Fraser-Brunner (1949) as subspecies of E. affinis, whereas E. alletteratus is accorded specific rank. In reality lineatus differs anatomically as much from the one as from the other, and has, in fact, a different vertebral structure and a different vertebral count. Similarly the writer is critical of such nugatory specific separations as proposed e.g. by Ginsburg (1953). Discussions of the latter type in particular will explain the emphasis in this report upon positive diagnostic characters. It is hoped that the following descriptions will supply a constructive addition to the knowledge of the group.

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