Periophthalmodon septemradiatus (Hamilton)

Khaironizam, M. Z. & Norma-Rashid, Y., 2003, First Record Of The Mudskipper, Periophthalmodon Septemradiatus (Hamilton) (Teleostei: Gobiidae) From Peninsular Malaysia, Raffles Bulletin of Zoology 51 (1), pp. 97-100 : 97-98

Periophthalmodon septemradiatus (Hamilton)

Material examined. – 20 ex., KMZ-NYR000306 KK (2), Malaysia: Selangor, Selangor River at Kampung Kuantan, coll. M. Z. Khaironizam & Y. Norma-Rashid, 6 Mar.2000 ; 10 ex., ZRC 41648 , Malaysia: Johor, Muar, Muar River below Tanjung Selabu, coll. Y. Y. Goh, 8 Sep.1997 ; 6 ex., ZRC 41172 , Malaysia: Johor, Muar, Muar River at Jorak, coll. Y. Y. Goh, 18 Nov.1996 .

Diagnosis. – No pelvic frenum, pelvic fins completely separated. Snout scaleless, isthmus completely scaled. Scales on entire body large and cycloid. Teeth of upper jaw in two rows: anterior teeth of outer jaw small caninoid and smaller in the inner row. First dorsal fins (D1) in the female poorly developed possessing 3-5 short spines, and in some specimens are rudimentary. In the male, the first dorsal fin is of moderate height with a concave margin and an elongated first spine with 12 unbranched spines ( Figure 2 ). Second dorsal fin (D2) with 12-14 spines (the first two unbranched). The first and second dorsal fins are contiguous. Pectoral and caudal fin spines are also branched. Table 1 shows the meristic and morphometric data of the specimens under KMZ-NYR000306KK (2).

Colour description. – Freshly dead specimens have dusky grey heads and, brown on dorsum, white on ventrum and numerous pale red and pale blue spots on snout, opercle and trunk. A dusky longitudinal stripe on the predorsum starts from eye and terminates under the end of D2 or just before the D 2 in certain specimens. Eight black, saddle-like blotches occur dorsally: first anterior to D1, second across base of D1, third between D1 and D2, fourth, fifth and sixth across base of D2, seventh between D2 and caudal fins and eighth anterior to caudal fin. Dorsal fins: D1 black with reddish margin and D2 dusky with a red margin. Caudal and pectoral fins greyish and numerous red and blue speckles on pectoral fins. Anal and pelvic fins dusky.

Preserved specimens are dark brown on body and white on ventrum. Black spots on body and the dusky stripe can only be seen in some specimens. The black blotches on dorsum also can be seen in preserved specimens. D1 black with a transparent margin, D2 dusky with dark brown stripes. Caudal, pectoral, anal and pelvic fin rays dusky.

Remarks. – Murdy (1989) recognised three species from the genus Periophthalmodon . They are distributed from Ganges Delta eastward to Indonesia, Papua New Guinea and Australia, but only one species, Pn. schlosseri , was recorded from Peninsular Malaysia ( Cantor, 1849; Koumans, 1953; Berry, 1972; Murdy, 1986, 1989; Takita et al., 1999).

The genus Periophthalmodon is distinguished from Periophthalmus by having a black stripe coursing posteriorly from the eye to the caudal peduncle, and by having two rows instead of one row of teeth in the upper jaw. These characters differentiate Pn. septemradiatus from the similar looking Periophthalmus weberi , which is known only from Papua New Guinea and Australia (Murdy, 1989).

The separated pelvic fins of Pn. septemradiatus differentiate it from its congeners. Pn. schlosseri and Pn. freycineti have a strong frenum across their pelvic fins which are totally united to form a round disk. Unlike its congeners, Pn. septemradiatus is also sexually dimorphic. In mature males, the dorsal fins are contiguous, and the first dorsal fin is very reduced on females ( Figure 2 ). In addition, adult Pn. septemradiatus is smaller (SL: about 40.0-60.0 mm) compared to Pn. schlosseri (SL: about 100.0-300.0 mm) and Pn. freycineti (SL: about 80.0-200.0 mm) (Murdy, 1989).

Periophthalmodon septemradiatus was found utilising the habitat that is far from the sea. Although under tidal influence, the water there was almost fresh, with a salinity that ranged between 1 and 3 ppt. In contrast, B. boddarti, Ps. chrysospilos and most other mudskippers live in the littoral zone on the foreshore where the salinity ranges from 30-34 ppt. (Chew & Ip, 1990; Clayton, 1993).

Ecology. – The specimens of Periophthalmodon septemradiatus examined by us were obtained from the banks of the Selangor River at Kampung Kuantan (3 11’N, 101 18’E). This study area ( Figure 1 ) is located about 15 km from the river mouth at Kuala Selangor, and about 64 km from northwest Kuala Lumpur. It was largely utilised for fishing, touristic and residential accommodation. A single species of mangrove, Sonneratia caseolaris was dominant. It formed a 10 metre wide belt above the mud banks, and ran parallel to the bund. Mature trees have brownish-grey bark and protruding pneumatophores that grow as high as 10 to 15 cm. The mangrove forest was relatively open with slightly over 15 plants per 6 square metres. There were also some small tributaries draining through stands of Nypa fruticans and village orchard. The mud-banks were gradually sloping and the substrate was extremely soft with high water content. Periophthalmodon septemradiatus was found on the mud banks and in the small tributaries along the upper reaches of the estuary. It was observed living sympatrically with the mudskippers Periophthalmus novemradiatus and Ps. gracilis . Along the upper reaches of the estuary at Kampung Kuantan, the water was fresh (0 ppt) at low tide. During extreme high tides, the salinities recorded in the river ranged from 1 to 3 ppt. Takita et al. (1999) found this species in a small stream at Tebing Tinggi, Sumatra, in a place similar to the present study area, but they did not report on the water salinity or the presence of sympatric mudskipper species there.

Figures

Fig. 2. Sexual dimorphism on Periophthalmodon septemradiatus [KMZ-NYR000306KK (2)]. a) Male: the first dorsal fin is of moderate height with an elongated spine and contiguous with the second dorsal fins. b) Female: the first dorsal fin is poorly developed and not contiguous with the second dorsal fins.

Fig. 1. Map of Selangor River at Kampung Kuantan, Selangor, showing known localities where Periophthalmodon septemradiatus were collected (triangles). Inset: map of Peninsular Malaysia with an additional locality (round spot) in Johor.