There are reports on the morphometric comparison of the yellowfin tuna obtained between the middle and eastern parts of the Indian Ocean^l)2), but none is found on the comparison of the specimens taken among the western and other divisions of the Ocean. This paper deals with the investigative results of the Sagamimaru, research boat of the Kanagawa Prefectural Fisheries Experimental Station.
The measurements of body parts were compared among four areas in the western part of the Indian Ocean, and also among the western, middle and eastern divisions of the Ocean (Table 1).
The lengths from the tip of snout to insertions of pectoral fin, the lst dorsal fin and ventral fin differ considerably for respective areas, but those from there to insertions of the 2 nd dorsal fin and anal fin and depths do not differ for respective divisions. This means that the anterior parts of the body differ for respective areas.
The anterior body parts of fishes obtained from the middle and eastern divisions of the Indian Ocean are longer, those parts of them taken from the areas W₁, W₂ and W₅ are shorter and those of fishes from the area W₄ are median length between the two groups.
The area of W₄ is situated in the southern of 3°30'-4°00'S., and more westward than the area of W₅ and the areas of W₁, W₂ and W₅ are located in the northern of 1°00'-2°30'..
Accordingly, it may be considered that the anterior body parts of fish, obtained from the middle and eastern divisions of the Indian Ocean, are long, those lengths of fish from the southern of 3°30'-4°00'S., median, and those of fish from the northern of 1°00'-2°30'S., short.