&lt;b&gt;On the taxonomy of the first record of rare deep-water rough shark species of Oxynotidae (Chondrichthyes: Squaliformes) in the western Indian Ocean&lt;/b&gt;

Sarah Viana,Mark W Lisher

doi:10.11609/jott.3916.10.6.11732-11742

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.

Highlights

Oxynotidae is a monotypic family of small to medium sized rare deep-water rough sharks with endemic regional geographical distributions on continental and insular shelves and upper continental slopes of the Atlantic and Pacific Oceans (Ebert et al 2013)
Members of Oxynotidae are characterized by having a body triangular in cross-section, conspicuously deep, arched dorsally and flattened ventrally at trunk, rough skin with large dermal denticles, head small and wide, snout blunt at tip and short with fringed anterior margin of nostrils, mouth circular with papillose lips and ventrally located, eyes rounded and conspicuously large, located laterally, spiracles large and crescent, located behind eyes, dorsal fins sail-like, conspicuously upright and tall, dorsal-fin spines conical, thick and markedly small, located prior to each dorsal fin and never transcending the fin apex, pectoral fins leaf-like, pointed distally at apex, and inconspicuous free-rear tips, lateral ridges prominent at trunk, caudal fin small and broadly sub-triangular with inconspicuous lower caudal lobe and evident subterminal notch
Oxynotus centrina is usually distinguished from its congeners by having grey or brownish grey body with broad dark brown blotches dorsal-laterally, eyes with heavy supra-ocular ridge and knobs, spiracles large and vertical (Compagno 2016), and few proportional external measurements (Yano & Matsuura 2002)

Summary

INTRODUCTION

Oxynotidae is a monotypic family of small to medium sized rare deep-water rough sharks with endemic regional geographical distributions on continental and insular shelves and upper continental slopes of the Atlantic and Pacific Oceans (Ebert et al 2013). Oxynotus centrina is usually distinguished from its congeners by having grey or brownish grey body with broad dark brown blotches dorsal-laterally, eyes with heavy supra-ocular ridge and knobs, spiracles large and vertical (Compagno 2016), and few proportional external measurements (e.g., dorsal fin-spines and first dorsal-fin apex, precaudal length and origin of first dorsal fin spine) (Yano & Matsuura 2002) It inhabits muddy and coralline algal bottoms of continental and insular shelves and upper continental slopes between 40–800 m depth, and is occasionally caught as bycatch during trawls and longlining (Ebert & Stehmann 2013; Ragonese et al 2013; Compagno 2016). Taxonomic problems on species of Oxynotus are discussed

MATERIAL AND METHODS

Findings

DISCUSSION