On the taxonomy of the first record of rare deep-water rough shark species of Oxynotidae (Chondrichthyes: Squaliformes) in the western Indian Ocean

Abstract

An immature female specimen of rough shark was collected south of Reunion Island in the Madagascar Basin in 2009 aboard R/V Dr. Fridtjof Nansen, representing the first official record of the family Oxynotidae in the western Indian Ocean. The specimen is herein identified as Oxynotus sp. due to morphological differences with its closely similar congeners O. centrina and O. bruniensis regarding morphometrics, shape of dorsal, pectoral and caudal fins, shape of the head and colouration, refuting the hypothesis of occurrence of these two species in the region. These results indicate that Oxynotus sp. is possibly an undescribed species. A general description of the external morphology, external morphometrics and photographs of Oxynotus sp. are provided. The specimen has a hepatosomatic index of 36.33% which reveals that it was possibly approaching maturation, suggesting that a viable population of Oxynotus sp. exists in the western Indian Ocean. Intraspecific variations in O. centrina from the Mediterranean Sea and eastern Atlantic Ocean are also noticed, requiring further taxonomic scrutiny.

Keywords

• madagascar basin
• morphology
• oxynotus
• rough sharks
• taxonomy
• western indian ocean.