Special Publication J.L.B. Smith Institute of Ichthyology ISSN: 0075-2088 Num. 58, 1997, pp. 1-8

A NEW SPECIES OF BOTHUS (PLEURONECTIFORMES: BOTHIDAE) FROM MOZAMBIQUE
by
D. A. Hensley

Department of Marine Science, University of Puerto Rico, Mayaguez, Puerto Rico 00681,

Code Number: FS97001
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ABSTRACT

Bothus swio is described based on one adult male specimen collected off the coast of Mozambique. Males of this species appear to differ from all known congeners because of their narrow interobital region. Other characters useful for its identification are lack of ocular appendages, relative positions of the anterior margins of the eyes, number of lateral-line scales, length and colour pattern of the ocular-side pectoral fin, lack of orbital spines, dorsal- and anal-fin ray counts, and lack of colour pattern on the blind side. Bothus swio most closely resembles B. pantherinus and B. tricirrhitus.

INTRODUCTION

Norman (1934) recognized six species of Bothus from the Indo-West Pacific: B. mancus (Broussonet, 1782), pantherinus (Ruppell, 1830), myriaster (Temminck and Schlegel, 1846), bleekeri Steindachner 1861, assimilis (Gunther, 1862), and ovalis (Regan, 1908). Although he was doubtful that B. ovalis and bleekeri were distinct from B. myriaster, Norman (1934) gave the range of B. bleekeri as Ceylon, Indo-Australian Archipelago, and the Hawaiian Islands. He included the Hawaiian Islands in the distribution because he synonymized B. thompsoni (Fowler, 1923) with B. bleekeri. Struhsaker and Moncrief (1974) showed that B. thompsoni is a distinct Hawaiian endemic. Most faunal works have not recognized B. bleekeri as a distinct species (e.g. Weber and de Beaufort 1929; Munro, 1955, 1967). Amaoka (1964) synonymized B. ovalis with B. myriaster. Bothus assimilis, known from China and Taiwan, may not be distinct from B. myriaster. Shen (1983) did not include B. assimilis in his study of the bothids of Taiwan because specimens were then unavailable. However, he illustrated both species in his 1984 book on the coastal fishes of Taiwan, but omitted B. assimilis in his more recent work (Shen, 1993). Kotthaus (1977) described two new species (B. ypsigrammus and tricirrhitus) from the Gulf of Aden and the eastern coast of Somalia. In summary, six or seven species of Bothus are currently recognized in the Indo-West Pacific.

During a recent fisheries survey off the coast of Mozambique by the South African Sea Fisheries Research Institute, a new species of Bothus was collected. This species is described in this paper.

METHODS

Methods for making counts and measurements followed those of Hubbs and Lagler (1949) with the following changes: because all dorsal- and anal-fin rays are unbranched, all ray elements were counted as individual rays; lengths of pelvic-fin bases were measured from the base of the first ray to the base of the last ray. Standard length (SL) was used throughout. Unless otherwise stated, measurements refer to those made on the ocular side. Measurements were made with dial calipers to the nearest 0.1 mm. Institutional abbreviations are as listed by Leviton et al. (1985).

Bothus swio, sp. nov.

Figure 1: Holotype of Bothus swio, SAM 33681, 157 mm SL, male.

DIAGNOSIS:

A species of Bothus having the following combination of characters: interorbital narrow in males, much less than diameter of eye; anterior margin of upper eye only slightly posterior to anterior margin of lower eye; males with no ocular tentacles or flaps, orbital spines, or colour pattern on blind side; second, third, and fourth pectoral-fin rays on ocular side greatly elongated in males, the second ray more than twice as long as head; all scales on eyed side ctenoid; dorsal-fin rays 90; anal-fin rays ca. 71; lateral-line scales 92.

DESCRIPTION:

Morphometrics expressed as percent SL: head length 28.1; body depth 51.3; snout length 7.5; upper-jaw length 9.7, blind side 9.9; lower-jaw length 13.2, blind side 14.3; lower-eye length 8.1, upper-eye length 7.9; interorbital width 1.7; pectoral-fin length 63.7, blind side 15.5; length of third pelvic-fin ray 11.3, blind side 7.8; length of pelvic-fin base 7.3, blind side 3.6; length of first dorsal-fin ray 6.7, of ray near middle of fin 12.2; length of first anal-fin ray 7.3, of ray near middle of fin 11.3; depth of caudal peduncle 11.1, length of caudal peduncle 2.2.

Morphometrics expressed as ratios of larger measurements: head length 3.6, body depth 2.0, both in SL. Measurements in head length: snout 3.7; upper-jaw length 2.9, blind side 2.8; lower-jaw length 2.1, blind side 2.0; lower-eye length 3.4, upper-eye length 3.6; interorbital width 17.0; pectoral-fin length 0.4, blind side 1.8; length of third pelvic-fin ray 2.5, blind side 3.6; length of pelvic-fin base 3.8, blind side 7.9; length of first dorsal-fin ray 4.3, of ray near middle of fin 2.3; length of first anal-fin ray 3.9, of ray near middle of fin 2.5; depth of caudal peduncle 2.5, length of caudal peduncle 12.6.

Dorsal-fin rays ca. 90; anal-fin rays ca. 71; pectoral-fin rays 11, blind side 9; pelvic-fin rays 6 (both sides); caudal-fin rays 17, dorsalmost 3 unbranched, ventralmost 2 unbranched; lateral-line scales ca. 92; gill rakers ocular side 0 + 9; vertebrae 10 +27.

Profile of head smoothly convex with indentation anterior to interorbital region. Interorbital region narrow and deeply concave, scaleless in middle of length. Anterior margin of upper eye slightly posterior to anterior margin of lower eye; no orbital spines, but anterior margins and interorbital margins high and sharp. Eyes without ocular cirri or flaps. Well-developed rostral spine on ocular side, none on blind side. Posterior end of maxilla extending to vertical through anterior margin of lower orbit. Nostrils on ocular side at same level as upper margin of lower orbit, anterior nostril tubular, posterior nostril with elevated edge and recurved lip; anterior nostril on blind side below first dorsal-fin ray, tubular; posterior nostril slit-like immediately behind anterior nostril. Tip of isthmus below posterior half of lower eye. Teeth in both jaws similar on ocular and blind sides, caniniform, uniserial, becoming slightly larger anteriorly. Gill rakers longer than wide with blunt tips.

Scales on ocular side ctenoid, cycloid on blind side; lateral line visible only on ocular side. Base of first pelvic-fin ray on ocular side at tip of isthmus; base of first pelvic-fin ray on blind side at same transverse level as fourth ray of pelvic fin on ocular side. Margin of caudal fin rhomboid, with tip rounded.

Colour in alcohol: Ocular side ground colour tan. Four rows of ocelli: 1) just below dorsal fin, 2) dorsal to lateral line: 3) ventral to lateral line, and 4) dorsal to anal fin. Three large dark spots on lateral line, 1) at junction of curved and straight sections, 2) on middle of straight section, and 3) near anterior end of caudal peduncle. Two dark areas anterior to upper eye and two dark bars across interorbital. Dorsal and anal fins with dark spots, both fins with distinct row of larger spots along fin-ray bases; caudal fin with dark spots, two near base of fin large. Pectoral fin with 6-7 very distinct black spots. Pelvic fin with large black spot on membrane between third and fourth rays on distal 1/3 of fin. Blind side cream coloured.

DISTRIBUTION:

Known only from the coast of Mozambique.

HABITAT:

Collected from a depth of 88 m with a bottom trawl.

ETYMOLOGY:

The name "swio" is the acronym for the southwestern Indian Ocean.

SEXUAL DIMORPHISM:

Most species of Bothus show sexual dimorphism in several characters, e.g. males with longer ocular-side pectoral fins and some sort of appendages on the eyes. In nearly all Bothus species the males have wider interorbital widths than females. Bothus pantherinus appears to show a difference in this character between males and females (Norman, 1934; Amaoka, 1969; Hensley, 1986), but this difference is very slight and has not been shown to be statistically significant. Because this description of B. swio is based on only one male specimen, we have no knowledge of which characters show sexual dimorphism. This specimen has well-developed testes, the second, third, and fourth ocular-side pectoral-fin rays elongated, and a rostral spine. The interorbital region appears to be the narrowest of any mature male of the known Bothus species. Based on sexual dimorphism in these characters in congeners, female B. swio probably have a similar or narrower interorbital region, no rostral spine, and a shorter ocular-side pectoral fin.

REMARKS:

The family Bothidae has yet to undergo a phylogenetic analysis; none of the genera are based on what have been shown to be derived characters. Bothus swio resembles species of Grammatobothus. The major character used to separate Grammatobothus from other bothid genera is the presence of the lateral line on the blind side (Norman, 1934, 1966). When this genus is compared to Bothus, several other differences are apparent in addition to the lack of a lateral line on the blind side in species of Bothus. In species of Grammatobothus the anterior dorsal-fin rays are somewhat prolonged in both sexes; in at least one species, G. polyophthalmus, these rays are longer in males than in females (Amaoka, et al., 1992). Amaoka et al. (1992) found that male G. polyophthalmus have one or two short, dark bars on the head that are absent in females. Neither of these sexually dimorphic characters are known from species of Bothus, including B. swio. Males of Grammatobothus species have elongated ocular-side pectoral fins. This is known for many species of Bothus as well. Although this fin is very long in the male holotype of B. swio, whether or not it is a sexually dimorphic character will not be known until females are collected. Most species of Bothus have been shown to be sexually dimorphic in interorbital width (wider in males), blind side colouration (dark colour pattern on blind side in males), head spination (present in males), and ocular appendages (present in males). Sexual dimorphism in these characters does not occur in Grammatobothus species. The male B. swio does have a well-developed rostral spine, but, again, no females have been collected. The holotype shows no blind-side colour pattern or ocular appendages. The scales on the blind side were carefully examined for lateral-line pores; none were located. In summary, since the main character currently used in separating the genera Grammatobothus and Bothus is the presence of a lateral line on the blind side in Grammatobothus, this new species is provisionally placed in the genus Bothus, although a future phylogenetic study may indicate its sister species is one of the Grammatobothus species.

Figure 2: Plot of interorbital width against SL. Data for Bothus tricirrhitus taken from Kotthaaus (1977).

COMPARATIVE MATERIAL EXAMINED:

The standard length and interorbital widths of twelve specimens of Bothus pantherinus , selected by size and sex, were examined from the lots: RUSI 3909, 5703, 13218, 17805, 17807, 17819, 30749, 44188, 15613.

ACKNOWLEDGEMENTS

I would like to thank Phil Heemstra and Paul Skelton for providing space and access to resources at the J. L. B. Smith Institute of Ichthyology, Elaine Heemstra for the fine drawing of the holotype, Butch Hulley, Liz Hoenson, and Michelle van der Merwe for assistance and loan of specimens during my visit to the South African Museum, Kunio Amaoka for his review of the manuscript, and the Hugh Kelly Fellowship Program (Rhodes University), the South African Foundation for Research Development, and the United States Fulbright Fellowship Program for supporting my work in South Africa.

LITERATURE CITED

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STRUHSAKER, P., & R. M. MONCRIEF. 1974. Bothus thompsoni (Fowler) 1923, a valid species of flatfish (Pisces: Bothidae) from the Hawaiian Islands. Fish. Bull., U. S. Dept. Comm. 72(1): 237-246.

TEMMINCK, C. J., & H. SCHLEGEL. 1846. Pisces (pp 173-269). In: Fauna Japonica, Parts X-XIV. P. F. von Siebold (ed.). Leiden.

WEBER, M., & L. F. DE BEAUFORT. 1929. The Fishes of the Indo-Australian Archipelago. 5. Anacanthini, Allotriognathi ... Heterosomata, Berycomorphi, Percomorphi (Kuhliidae ... Centropomidae). E. J. Brill, Leiden, 458 pp.

Copyright 1997 J.L.B. Smith Institute of Ichthyology

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