Rare batfish species, Halicmetus ruber Alcock, 1891 (Lophiiformes: Ogcocephalidae), from the Indian Exclusive Economic Zone

Abstract

The first authentic record of deep-sea fishes was made with the help of those collected by R. I. M. S. Investigator in the book, ‘Indian Deep Sea Fishes in the Indian Museum’. The Fishery Survey of India, concentrating principally on the continental shelf region, carried out research on deep-sea fishes within the Indian Exclusive Economic Zone (EEZ). Data on deep-sea fish fauna are scarce, and the only available information is from the fishing cruises of FORV Sagar Sampada as part of its deep-sea finfishes stock assessment programme. Earlier studies on the ogcocephalid genus Halicmetus showed that it comprised two nominal species: H. ruber Alcock, 1891 collected from the Andaman Sea and H. reticulatus Smith and Radcliffe, 1912 from the Philippines (Ho et al., 2008). However, later studies revealed that the genus Halicmetus comprises four species, of which H. reticulatus is the only member with dorsal fin rays, whereas H. nigra sp. nov., H. ruber and H. cf. ruber lack these dorsal fin rays. Halicmetus ruber Alcock, 1891 is a small benthic fish (<10 cm total length) characterised by the absence of a dorsal fin (unique among batfishes) and no colour pattern on its disk. Halicmetus reticulatus is characterised by having two or three dorsal fin rays and a reticular disk colour pattern. However, Brauer (1906) recorded seven specimens with a small dorsal fin, purportedly H. ruber from the Andaman Sea. Furthermore, Smith and Radcliffe (1912) mentioned H. ruber specimens lacking a dorsal fin ray that were collected by the RV Albatross from the western Pacific. Weber (1913) described a subspecies, H. ruber marmorata, based on five specimens (ZMA 101.893) collected in Indonesia, and synonymised to H. ruber by Bradbury (1967). On the basis of all ogcocephalid genera morphological characteristics, Bradbury (1967) concluded that the Halicmetus head is distinguishable from others in that it: is markedly depressed, with the face flattened (truncated) and distinctly upturned; shows the presence of bucklers and small tubercles; has two gills, with gill filaments only on the 2nd and 3rd gill arches; the pectoral pedicles are not well attached to the body wall; has an interrupted lateral line and with the illicial bone split into two long processes. Halicmetus specimens are uncommon. Hence, an attempt has been made here to redefine this deep-sea fish by comparing its morphometrics and meristics with those of H. cf. ruber and H. reticulatus from the Pacific Ocean. Materials and methods