Phuket mar. biol. Cent. Res. Bull.76: 19–23 (2019) FIRST RECORD OF DOUBLE-LINED MACKEREL Grammatorcynus bilineatus (Rüppell, 1836) FROM THE GULF OF THAILAND Vachira Lheknim Department of Biology, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand Corresponding author: [email protected] ABSTRACT: The double-lined mackerel Grammatorcynus bilineatus (Rüppell, 1836), is recorded for the first time in the Gulf of Thailand. This species differs from the congeneric G. bicarinatus (Quoy and Gaimard, 1825) in having 18–24 total gill rakers (vs. 12–15 in the latter), 22–26 pectoral fin soft rays (vs. 21–24) and fleshy eye diameter 4.0–6.7 % fork length (vs. 3.1–4.6). It is believed that it reached the Gulf of Thailand from the South China Sea, despite the lack of a record from there, due to its well documented presence in the Pacific. Keywords: Grammatorcynus bilineatus, Scombridae, Gulf of Thailand, first record INTRODUCTION widespread in the Indo-West Pacific, with more gill rakers (18–24), a larger fleshy eye (4.0–6.0% The double-lined mackerel, Grammatorcynus fork length, FL), and a smaller maximum size (60 bilineatus (Rüppell, 1836), is a migratory species cm FL); and the shark mackerel G. bicarinatus, inhabiting tropical and sub-tropical waters of the restricted to the waters of northern Australia and Indo-Pacific from the Red Sea east to the Andaman southern New Guinea, with fewer gill rakers (12–15), Sea, the Java Sea, the Philippines, Ryukyu Islands, a smaller fleshy eye (3.1–4.6% FL), and a larger southern Japan, Irian Jaya, Papua New Guinea, maximum size (110 cm FL). Later Collette and northern coasts of Australia, Solomon Islands, Gillis (1992) used osteological evidence to confirm New Caledonia, Caroline and the Marshall Islands, the difference between these two species and they and Fiji (Collette and Nauen, 1983; Collette, 1984; included a summary of literature and its synonymy. 2001; Nakabo, 2002). According to this information, In Thailand, Tongyai (1966, cited in Collette its geographical distribution ranges from about and Gillis, 1992) listed the double-lined mackerel 30°E to about 180°E and from 30°N to 20°S, and G. bilineatus under the name of G. bicarinatus covers parts of the tropic and subtropic areas of the based on specimens from the Andaman Sea (see Indian and Pacific Oceans (Fig. 1). Within this also Satapoomin, 2011). However, the species has restricted range, the double-lined mackerel is an never been recorded from the Gulf of Thailand epipelagic species that is mostly found in shallow (Thiemmedh, 1968; Suvatti, 1981; Monkolprasit et reef waters where it forms small groups close to al., 1997; Yoshida et al., 2013). A reference list on reefs, mixed with other scombrids or as solitary this species can be found in http://www.fishbase. fish (Silas, 1963). org, which lists 33 countries recorded within the The taxonomic history of G. bilineatus is above known range, lacking a record from the Gulf considerably complex. Earlier, most authors of Thailand (Froese and Pauly, 2018). mentioned that the double-lined mackerel found The objective of this note is to report on the in Indo-Pacific belonged to the congeneric species first records of double-lined mackerel in the Gulf G. bicarinatus (Quoy and Gaimard, 1825) (see also of Thailand and the co-occurrence of other species Silas, 1963). In 1983, Collette (1983) and Collette in the same catch, which are capture records that and Nauen (1983) recognized and differentiated represent significant extensions of the species two species: the double-lined mackerel G. bilineatus, normal distributions. 20 Phuket mar. biol. Cent. Res. Bull. Figure 1. Distribution of double-lined mackerel, Grammatorcynus bilineatus (Rüppell, 1836), with a new record from the Gulf of Thailand shown by a triangle. Base map was redrawn from Silas (1963), Collette and Nauen (1983) and Collette (2001). MATERIALS AND METHODS RESULTS AND DISCUSSION On 13 th August 2011, while searching for short Two individuals (203–214 mm FL/ 192–202 mackerel Rastrelliger specimens for a morphometric mm standard length) of the double-lined mackerel study at the small fishing village in Patiew District, were collected on the west coast of the Gulf of Chumphon Province, two G. bilineatus specimens Thailand outside their known distribution range were observed in the catch of an artisanal fisherman (Fig. 1). Other measurements are given in Table operated at Kai Island, a small coral-fringed island 1. In most characters, the specimens are morpho- approximately 3 km off the shore in front of metrically and meristically within the ranges given the village, in the western Gulf of Thailand (10° in Collette and Gillis (1992) for Grammatorcynus 42.292´ N; 99° 24.669´ E, Fig. 1). These double-lined bilineatus, however, slightly larger fleshy eye mackerel were captured using monofilament gill diameter between these specimens and previous nets intended for mackerel, set early morning studies were noted (6.3–6.7% FL vs. 4.0–6.0% FL). around 05:30 am and retrieved about 07:30 am. The double-lined mackerel, G. bilineatus, can These were brought to the author’s attention after be distinguished from other scombrids in the region they were separated from the short mackerel and by having two lateral lines and three caudal keels. thrown away with other trash fishes. From a closer The upper-most lateral line is slightly convex, brief look, these specimens have double lateral originates near the dorsal portion of the opercle, lines and three caudal keels. The specimens were and continues posteriorly until it converges with frozen and transported back to Prince of Songkla the second lateral line, just anterior to the median University. Identification was done using the key caudal keel. The lower lateral line originates from by Collette and Nauen (1983) and Collette (2001). a point below the first four spines of the dorsal fin. The specimens were preserved in 95% ethanol, It starts ventrally, running under and posterior to catalogued as PSUZC 20110813-01.01–02, and the pectoral fin, and abruptly turns into a concave deposited in the fish collection of the Prince of line that continues posteriorly until meeting the Songkla University Zoological Collection (PSUZC) dorsal lateral line (Fig. 2) as a usual lateral line at the Princess Maha Chakri Sirindhorn Natural pattern recognized for G. bilineatus by Collette History Museum, Prince of Songkla University and Gillis (1992). in Hat Yai, Songkhla, Thailand. Morphometric Fin ray counts include 12 spines in the first measurements and counts were taken from the dorsal fin, 11 soft rays plus 6 finlets in the second study of the fresh specimens by Collette and Gillis dorsal fin, 11 soft rays plus 6 finlets in the anal fin, (1992). 24 to 25 soft rays in each pectoral fin and 5 soft 21 First record of double-lined mackerel Grammatorcynus bilineatus rays in each pelvic fin. The first gill arch with 6 of the specimen of G. bilineatus in the Gulf of gill rakers on upper limb and 15 to 16 on lower Thailand. First, the lack of previous records in the limb (total 21 to 22). The upper body of freshly Gulf of Thailand may be the consequence of a low caught specimen, especially the dorsum of the head sampling effort. Second, the presence ofG. bilineatus and the region above the upper lateral line, is bluish in the Gulf of Thailand waters may be the result green with a metallic tint. The belly and the under- of recent colonization from the western Pacific side of the body are silvery white. The inter-spinous perimeter. Despite the lack of earlier records in the membranes of the first dorsal and the fins are tinged Gulf of Thailand, the connection of oceanographic light blue, while the inner edge, the tips and the conditions between the western Pacific, the South inner ray of the caudal fin are tinged yellowish. China Sea and the Gulf of Thailand along with There is a patch of light red in the region of the extreme oceanographic variations may account for chin, below the eye in fresh specimen. The iris is the natural introduction in this situation. conspicuously whitish (Fig. 2). Grammatorcynus bilineatus is likely a part of Co-occurring species. Rastrelliger brachysoma the occasional catch in the artisanal fishery in the (Bleeker, 1851), R. kanagurta (Cuvier, 1817), Gulf of Thailand. Interviews with local artisanal Megalaspis cordyla (Linnaeus, 1758), Atule mate fishermen suggest that the double-lined mackerel is (Cuvier, 1833); Carangoides armatus (Rüppell, native in the area, and is not rare. Although we have 1830), Scolopsis ciliata (Lacepède, 1802); Terapon no previous records of G. bilineatus in the Gulf of theraps Cuvier, 1829; Abudefduf septemfasciatus Thailand, it is possible that an unknown population (Cuvier, 1830); Pempheris oualensis Cuvier, 1831 exists in this area, as suggested in Randall and Lim and several immature with initial phase of Scarus (2000). Presently, G. bilineatus is listed as Least spp. were also obtained from the same haul with Concern species by IUCN (2018). It is, however, the double-lined mackerel. very important to provide information on G. bilineatus In summary, our record from the Gulf of distribution to avoid incorrect identification. Thailand expands the current knowledge on the This new record of G. bilineatus in the Gulf distribution of the double-lined mackerel, G. bilineatus, of Thailand extends the distribution range known in the South China Sea, extending it into the Gulf for this species, constitutes a large latitudinal jump of Thailand. Information on biology, distribution of >1200 km northward from the coastal waters of and population trends of the species along the Gulf East Malaysian, the previously known neighbor of Thailand is needed.