Journal of the Marine Biological Association of India

Volume 15 Issue 1

Morphology and distribution patterns of the whalefishes of the family Rondeletiidae.

John R. Paxton
Abstract

Midwater fishes of the family Rondeletiidae are known from relatively few individuals taken in the Indian, Atlantic and Pacific Oceans. Two species have been described, but these have been confused in some previous works. Rondeletia bicolor can be distinguished from R. loricata by the presence of a greater number of vertical rows of lateral line pores, a bony sphenotic hook over the orbit, and the lack of expanded frontals, supratempbrals and cleithra. Although other meristic characters overlap, the mean frequencies of dorsal and anal fin rays, vertebrae, and gill rakers are different in the two species.

The osteology of R. bicolor was described by Parr (1929). The skeleton of R. loricata is basically similar to that of its congener, but differences in the following elements are apparent: lateral ethnioids, frontals, sphenotics, supraoccipitals, hyomandibulars, symplectics, quadrates, epipteural rib origins, caudal skeletons, and pectroral girdles. As in R. bicolor, the skeleton of R. loricata is characterized by large amounts of cartilage.

Although the number of specimens examined was small, less than 20 of each species, certain trends in distributional patterns are indicated. The center of vertical distribution for each species is apparently below 1000 metres, although individuals of each have been taken as shallow as 350-400 metres. Due to the paucity of data, no estimation of vertical distribution is possible. The vast majority of captures have been of solitary individuals. R. bicolor is apparently restricted to the western North Atlantic Ocean and Caribbean Sea west of 600'W; the limited range is not characteristic of previously studied midwater fishes from the area. R. loricata appears to be cosmopolitan in distribution made in transitional areas near water mass boundaries. However, the Atlantic and Indian Ocean collections show no correlation with either water masses or areas of productivity. In the Indian Ocean R. loricata has been taken by the International Indian Ocean Expedition in both Indian Central and Indian Equatorial waters. Previous captures referable to this species include localities off the southeast coasts of both Indian and South Africa.

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Date : 31-08-1973