First record of the coloured righteye flounder, Poecilopsetta colorata (Teleostei: Poecilopsettidae) from the Sakalaves seamounts in the Mozambique Channel

The coloured righteye flounder, Poecilopsetta colorata Günther, 1880 was previously known from the eastern Indian Ocean to the South China Sea and Indonesia. Here, a new record from the western Indian Ocean is reported. The new record is based on a specimen collected on the Sakalaves seamounts at 375 m in depth in the Mozambique Channel during a recent oceanographic survey. Four other teleost fish species including an uncommon ophidiid species, Neobythites somaliaensis Nielsen, 1995 were also collected on the same seamounts. The presence of P. colorata in the Mozambique Channel suggests a broad and Indo-West Pacific wide distribution for this relatively rare deep-sea species. The sequence of the cytochrome oxidase subunit-I for the collected specimen is provided as a genetic reference for further DNA barcoding and systematic studies.

The authors examined 55 fish specimens collected during the 32-day multi-disciplinary cruise (campaign: PAMELA-MOZ01) in 2014 of the R/V Atalante deployed by the French Oceanographic Fleet in the Mozambique Channel in the western Indian Ocean. Among them, one specimen was identified as P. colorata.
The purpose of the present work is to record this species in the ichthyofauna of the Mozambique Channel and provide a molecular sequence from a mitochondrial gene as the genetic reference for further DNA barcoding and systematic studies.

Methods
The materials described in the present paper were collected during the cruise PAMELA-MOZ01 of the PAMELA project in 2014 conducted by the R/V Atalante (Olu, 2014) on the collection sites from three of the explored zones, the slope of the Glorieuses islands, the slope of the Mahajanga basin off Madagascar, and the Sakalaves seamounts on the southern Davie ridge (Fig. 1). The Warén dredge, NIWA seamount sledge and beam trawl were used for sampling at a total of eight sites. The geographic coordinates of the sites, depths, and methods for the deployments are listed in Table 1, and the collected samples are listed in Additional file 1 : Table S1. The specimens examined were deposited in the National Natural History Museum of Paris (MNHN). Muscle tissue samples excised from the specimens for genetic studies were preserved in 95 % ethanol and stored at −20°C in the Marine Biodiversity and Phylogenomics laboratory at the Institute of Oceanography, National Taiwan University, Taipei with tissue identification numbers from WIO 001 to WIO 055 (Additional file 1 : Table S1).
Whole genomic DNA was extracted from the tissue sample (WIO 041) of the P. colorata specimen using an automated extractor: LabTurbo 48 Compact System and LGD 480-500 kits (Taigene Biosciences Corp.) following the manufacturer's protocol. A fragment of the mitochondrial protein-coding gene cytochrome oxidase subunit I (COI) was amplified and sequenced for this study. Protocols for collecting molecular data follow those outlined in Ward et al. (2005). Six available COI sequences from two congeneric species (P. natalensis [n = 5] and P. hawaiiensis [n = 1]) were retrieved from Genbank and compared with our obtained sequence. The sequence alignment was conducted manually using Se-Al v2.0a11 (Rambaut, 2002). The variable nucleotide sites and genetic distance (uncorrected pairwise p-distance) among sequences and were calculated using PAUP* (Swofford, 2002).

Diagnosis
The counts of dorsal and anal fin rays and lateral line scales are considered as key features for diagnosing species of Poecilopsetta (Hoshino et al., 2001;Kawai et al., 2010). These counts in our examined specimen were 58, 48, and ca. 102-105, which fall into the ranges of the three characters for P. colorata (55-62, 46-53, and 90-124) and P. praelonga (57-65, 45-55, and 91-113) as being described in Kawai et al. (2010). The former species can be easily distinguished from the latter in having a deeper body (body depth 1.9 to 2.6 times in SL vs. body depth 3.8 to 4 times in SL) and a longer upper-jaw (upper-jaw length 3 to 3.5 times in head length vs. upper-jaw length 3.6 to 3.7 times in head length) (Hensley, 1997). Our specimen was diagnosed with body depth 2.3 times in SL and upper-jaw length 3.2 times in head length. All these characteristics combined together indicate our specimen is P. colorata.

Remarks
Based on the new record in this study, the distribution of the species extends to the western Indian Ocean from its previously reported area. The four other teleost fish species also collected from the same seamounts are: Neobythites somaliaensis (Ophidiidae), Pentaceros capensis (Pentacerotidae), Symphurus sp. 2 (Cynoglossidae), and Paratriacanthodes retrospinis (Triacanthodidae) (Additional file 1: Table S1). N. somaliaensis is an uncommon ophidiid species that was described based on specimens collected on the upper continental slope in the Gulf of Aden (Nielsen, 1995). The present record in the Mozambique Channel is new. This species is most similar to the common Neobythites species, N. analis Barnard 1927, from this region (Nielsen et al. 1999;; it differs from N. analis by the distal parts of both dorsal and anal fins being black (Fig. 4).

Discussion
Although some flatfishes including poecilopsettids have large and presumably long-lived larvae that could enhance the probability of achieving long-distance dispersal over large areas (Evseenko, 2000), widespread species crossing two oceans are rare in poecilopsettids (Munroe, 2005). In Poecilopsetta, P. colorata and P. praelonga are the only two species known to have a wide distribution ranging from the eastern Indian Ocean to the western Pacific Ocean (Quéro et al., 1988;Hensley, 1997). The record of P. colorata in the western Indian Ocean presented here confirms a wide and an extended distribution for this poorly known deep-sea species. The African righteye flounder, P. natalensis, also occurs in the western Indian Ocean. The extension of its distribution into the western Pacific has been suspected because of an unconfirmed record reported in Taiwan (Hensley, 1997). In this study, one of our compared COI sequences of P. natalensis was from the South China Sea (Fig. 3), confirming the presence of this species in the western Pacific Ocean. It is worthy to mention that the genetic distance between this sample of P. natalensis and others from South Africa is very low, from zero to 0.64 % of nucleotide divergence (corresponding to a single nucleotide difference), despite the large distance between the two sampling sites (Fig. 3). A genetic break corresponding to the geology that separates the Indian population from the Pacific one is often present in widespread marine Indo-West Pacific species (Borsa et al., 2016); it was not observed in P. natalensis.  Availability of data and material Sequence data are available in GenBank from National Center for Biotechnology Information; specimens are available from National Museum of Natural History, Paris, France.
Authors' contributions WJC contributed to the conception and design of the work, analyzed, interpreted the data, and wrote the paper; JNC collected the data and wrote the paper; JEP collected and managed the samples; KO led the cruise of sample collection and revised the paper. All authors read and approved the final manuscript.

Consent for publication
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