First record of Evoxymetopon taeniatus (Actinopterygii: Perciformes: Trichiuridae) from the Philippines

The channel scabbardfi sh, Evoxymetopon taeniatus Gill, 1863 has not been known from the Philippine waters. Our presently reported fi nding of two specimens (114.5 and 133.1 cm SL) of this species from the Philippines extends the range of this species to the central Indo-Pacifi c. The specimens captured were both male, one with developing gonads, and the other one—mature. We examined and described the fi sh found, providing morphometric and meristic analyses. The species can be distinguished from its congeners by having a convex upper head profi le, steep sagittal crest slope, 82 dorsal fi n rays with a defi ned notched at the tenth ray, a black dorsal fi n membrane before the notch, and 15 externally visible anal fi n rays that are bound with a membrane. The analyses included also relations with size of the four known Evoxymetopon species. Only one signifi cant relation was revealed by the regression analyses—between SL and % pre-anal length. We provided also an updated identifi cation key for the genus.

The trichiurids, commonly known as cutlassfi shes, hairtails, or scabbardfi shes, are widely distributed in tropical to warm temperate waters. They typically live close to the bottom on the continental shelf and the upper slope, reaching the depths of 50-1500 m (rarely 2000 m), with many species exhibiting diel vertical migrations (Nakamura and Parin 1993). At present, there are 47 valid species of trichiurids (Eschmeyer and Fong 2016), belonging to 11 genera . Of these, 9 species have been reported from the Philippine waters. "Trichiurus japonicus Temminck et Schlegel, 1844" was not among them. While the latter was earlier reported by Herre (1953) as a separate species, it is now considered a junior synonym of the wide-spread species Trichiurus lepturus Linnaeus, 1758(Carpenter and Niem 2001, Froese and Pauly 2016. Chakraborty et al. (2006), however, believe that T. japonicus is a valid species, as inferred from its DNA analysis.
Trichiurids make up a large fi shery worldwide, with total landings amounting to 1.26 million t in 2014 (Anonymous 2016c), most of which were caught in the north-west Pacifi c. In the Philippines, annual hairtail landings from 2002-2014 approximated 15 000 t per year (Anonymous 2016a) which is only 0.7% of the total marine-fi sheries landings in the country. This paper reports the fi rst records of the channel scabbardfi sh, Evoxymetopon taeniatus Gill, 1863, in the Philippine waters. Two specimens of E. taeniatus were recorded from catches of modifi ed hook and line fi shing on two different occasions off the coast of Naba, Culasi in Antique, in western Panay Island central Philippines ( Fig. 1) from 20 April to 10 May 2016. There are to date 53 recorded occurrences of this species worldwide (Anonymous 2016b), but only a few references on their biology are available. The species is reportedly more widespread in the west Atlantic (Froese and Pauly 2016). In the west Pacifi c, reports on its occurrence are limited to Japan, Taiwan, and Korea.
Two specimens of Evoxymetopon taeniatus were identifi ed in this study. The fi rst specimen measured 114.5 cm SL, while the second one-133.1 cm SL. Both specimens were caught using handlines modifi ed to catch trichiurids (by means of baited hooks tied to and suspended from the ends of a 1.2 m iron rod attached in the middle to a cylindrical lead weight at the end of the main fi shing line). Identifi cation of the species followed Gill (1863), Nakamura and Parin (1993), Sakiyama et al. (2011), Fricke et al. (2014, and Hata et al. (2015).
Standard morphometric measurements were taken following Hata et al. (2015), whereby length measurements are expressed as percentages (%) of the specimen's standard length (SL). Some modifi cations in fi n counts were made, such as instead of listing down the number of total external fi n rays (spinescent + external easily distinguishable rays), the count includes only the visible and distinguishable external fi n rays (Fricke et al. 2014). Hence, external anal fi n ray counts are presented as x + 15, where x is the number of spinescent anal rays. This modifi cation was done because precise counting of the spinescent rays is diffi cult due to their very minute size, and are thus prone to miscounting. Another modifi cation was the addition of the number of notched dorsal fi n elements and the number of dorsal fi n elements with a blackish membrane. These characteristics were added to help in distinguishing this species from other closely-related species in the family, where references are relatively scarce. Aside from the above, sex and maturation stages of the specimens were also noted.
Measurements and counts of Evoxymetopon taeniatus and of other Evoxymetopon species from different authors (Gill 1863, Nakamura and Parin 1993, Fricke et al. 2014, Hata et al. 2015, Sakiyama et al. 2011 were compiled and used in this study to examine relations with size and to update the identifi cation key of the genus. For Sakiyama et al. (2011), length measurements were converted to %SL to standardize the format and for easier comparison. Simple linear regression was employed to quantify the relations.
Family Trichiuridae Rafi nesque, 1810 Genus Evoxymetopon Gill, 1863 Evoxymetopon taeniatus Gill, 1863 The specimens in this study were both males, with the smaller specimen (114.5 cm SL) representing the gonad developing stage, while the larger one (133.1 cm SL)-in mature stage. Detailed descriptions of the specimens are presented below. Short description of the Philippine specimens. Meristics and morphometrics are given in Table 1. Body elongate, slender, deep and highly compressed with triangular pectoral fi n, reduced scale-like pelvic fi n (Fig. 2D), and small forked caudal fi n (Fig. 2E). Body silvery white, with slight reddish brown cast dorsally and several longitudinal yellow stripes on body. Head oblong with steep sagittal crest (Fig. 2C). Dorsal fi n elements of sub-equal length: 82, with defi ned notch at 10th element ( Fig. 2A-C). Colour of dorsal fi n membrane before notch black and transparent thereafter ( Fig. 2A-C). Externally visible anal fi n rays: 15. Comparison with other species. The channel scabbardfi sh, Evoxymetopon taeniatus, is externally similar to Evoxymetopon moricheni Fricke, Golani et Appelbaum-Golani, 2014, which also has a steep slope in the anterior part of the head, a crescent-shaped nostril, and no fi lament on the fi rst dorsal fi n spine. They however differ in the following features: E. taeniatus has 15 externally visible anal fi n soft rays, versus 17 in E. moricheni; 19 lower gill rakers (vs. 13 in E. moricheni); silvery white body with longitudinal stripes (vs. plain silvery body without stripes); anterior head portion without blackish margin (vs. blackish margin on head continuing along the anterior half of the dorsal fi n base); 1st to 9th dorsal fi n elements with blackish membrane (vs. 1st to 5th elements only); and dorsal fi n notched at the 10th element (vs. 8th through 9th element notch) (Fricke et al. 2014). Evoxymetopon taeniatus is further distinguished from the other species of the genus by its lack of a fi lament in the 1st dorsal fi n spine. The fi lament is sword-like in Evoxymetopon macrophthalmus Chakraborty, Yoshino et Iwatsuki, 2006 and elongate in Evoxymetopon poeyi Günther, 1887. It has crescent-shaped nostrils (Nakamura and Parin 1993), although the shape is not clear in our specimens, and 82 (range 81-82) dorsal fi n elements, while E. macrophthalmus and E. poeyi have slit-like nostrils and 90 and 91-93 dorsal fi n elements, respectively. Evoxymetopon taeniatus further differs from E. macrophthalmus by not having a blackish margin on the head, and from E. poeyi by having 15 externally visible anal fi n rays (vs. 20) (Fricke et al. 2014). Morphometric trends. Fin counts and %SL measurements of Evoxymetopon from Sakiyama et al. (2011) and Hata et al. (2015) were included in the analysis for morphometric trends (Table 1). Thus, 6 specimens were analysed for possible relations between SL and the other morphometric measurements. The regression analyses showed only one signifi cant relation (Fig. 3), between SL and % pre-anal length (r 2 = 0.909, P = 0.003). The number of dorsal fi n elements, as well as lower gill raker counts also tend to increase with size, but these covered very narrow ranges (Table 1)   shape is not readily distinguishable from our specimens and from the fi gures of Nakamura and Parin (1993). All characteristics mentioned in the key below are based on Gill (1863), Nakamura and Parin (1993), Chakraborty et al. (2006), Sakiyama et al. (2011), Fricke et al. (2014, and the presently reported study. All illustrations in the guide are adapted from Nakamura and Parin (1993). 1a. From 78 to 88 dorsal fi n elements, 1st dorsal fi n spine not elongate or no fi lament and shorter than the second, head profi le with a steep sagittal crest slope (Fig. 4B), dorsal fi n with a notch (Fig. 5B) ---------→2 1b. More than 90 dorsal fi n elements, 1st dorsal fi n spine elongate or sword-shaped, head profi le uniformly convex or with a gentle sagittal crest slope (Fig. 4A), dorsal fi n without a notch (Fig. 5A)  of Evoxymetopon (Family Trichiuridae) is presented below. All species have continuous single dorsal fi n, small forked caudal fi n, and reduced (scale-like) pelvic fi ns (Fig. 2). Although, the shape of the nostril (slitlike vs. crescent-shaped) is one of the distinguishing characteristics of the four species, this character is not included in the identifi cation guide because the nostril 3b. From 92 to 93 dorsal fi n elements, 1st dorsal fi n spine elongate (Fig. 4A),

externally visible anal fi n rays 20 ------------------→ E. poeyi
Remarks. This is the fi rst report of the occurrence of Evoxymetopon taeniatus in the Philippines and also the fi rst to analyse meristic and morphometric trends of the species with relation to fi sh size. The two specimens identifi ed were both caught off the coast (depth > 30 meters) of Culasi, Antique in western Panay. Several attempts were made (until July 2016) to acquire additional samples from the same area as well as in the neighbouring municipalities, but none were successful. The species is benthopelagic and therefore not easy to catch. Perhaps the two specimens mixed together with the more commonly caught hairtail, Trichiurus lepturus, which were locally abundant at shallower depths in April and May.
One of the specimens (133.1 cm SL) identifi ed was in mature stage while the other had its gonads in the developing stage. These fi ndings are the fi rst reports of sizes of mature individuals of the species. Based on the stages of the specimens, we estimate that the length at fi rst maturity is 114.5-133.1 cm SL. The larger identifi ed specimen (2.0 kg) also weighed more than the maximum recorded weight of the species listed in FishBase (1.7 kg) (Froese and Pauly 2016), although the largest specimen ever reported (163.8 cm SL) was caught in Japan (Sakiyama et al. 2011).
A detailed description of the species, as well as of other congeners is provided in Fricke et al. (2014). Their study, however, did not mention the number of dorsal fi n spines with blackish membrane, nor the dorsal fi n notch, which may be helpful in distinguishing one species from the other. Both specimens from the presently reported study show a blackish membrane covering the fi rst nine dorsal fi n spines ( Fig. 2A-C) and a notch at the 10th dorsal fi n spine (Fig.  2C). In E. moricheni, the blackish membrane is limited to the fi rst fi ve dorsal fi n spines only, while the notch (inferred from the pictures of Fricke et al. 2014) is between the eighth or ninth dorsal fi n spines. Note that the new taxon name in Fricke et al. (2014) is available from the fi rst online version, pages 1-4, published on 14 March 2014.
The only signifi cant trend in morphometrics was the increase in the pre-anal length in larger specimens, indicating that the anterior body grows more than the tail portion as individuals increase in size. This ontogenetic trend may be related to increased swimming abilities accompanying the shift from feeding on plankton and small fi sh as juveniles (Froese and Pauly 2016), to ambush fast swimming nekton such as anchovies, sardines, carangids, and squids (Chiou et al. 2006, Bittar et al. 2012 as adults. The relation between the size (SL) and the rest of the measurements were either too variable or covered differences that were too small to show signifi cance. For example, the orbit diameter differed by only 1 percentage points of SL (3.1% and 2.1%, respectively) ( Table 1) across the size range of the fi sh considered, but this small difference translates to a 30 percentage point relative change in the eye to body ratio, a feature that is important for visual feeders (Schmitz and Wainwright 2011). Trichiurids, however, are benthopelagic inhabitants of the continental shelf and slope (Nakamura and Parin 1993), where light penetration is limited. As predators, they rely heavily on other senses, such as chemo-and mechanoreception, rather than on vision (Mauchline and Gordon 1986). According to Bone and Moore (2008), trichiurids rely on the receptors in their lateral line in detecting preys via particle displacement. . This study reports the fi rst record of the channel scabbardfi sh, Evoxymetopon taeniatus, in the Philippine waters, thus extending its known geographical distribution to the central Indo-Pacifi c. Meristic and morphometric trends with size and maturation stages were also analysed, which is the fi rst for the species. Detailed descriptions and updated identifi cation key for the four known Evoxymetopon species are also presented which will be helpful with their future identifi cation.

ACKNOWLEDGMENTS
The authors would like to thank Dr. Hiroyuki Motomura of the Kagoshima University Museum and JSPS CC-RENSEA Program for validating the identifi cation and information of the species; researchers of the OceanBio Lab for assisting with the collection, identifi cation, and photographic documentation; and the RARE, Inc. for funding the project.  Nakamura and Parin (1993)