Genus Periophthalmus
Bloch and Schneider, 1801

This mudskipper genus is found in the eastern Atlantic, Indian and western Pacific oceans. There are 12 species in the genus as yet undefined by a synapomorphy (Murdy, 1989). The pelvic fins are only partially united or may be totally separate. There are usually 12-14 pectoral fin rays, 4-17 first dorsal fin spines, and 8-13 second dorsal and anal fin rays. Scales are cycloid and cover the whole body and head except for the snout, isthmus and interorbital region in most species. Caninoid teeth are present in both jaws as a single row, with the anterior ones larger and pointed. The eyes are erectile and have a dermal cup covering the lower portion. There is a median fleshy ridge anterior to the eyes.

Mudskippers are found on muddy shores associated with mangroves but also venture into rivers. They spend much time out of the water.

Periophthalmus waltoni
Koumans, 1955

Common names

gel-cheragh (= mud-eater, mud-grazer), mahi-sag (= dog fish), gel khorak.

[shelambo, abou-shlembo or abu-shelamboo in Arabic; gullo in Pakistan; dark-blotched mudskipper, Walton's mudskipper, spotted mudskipper].

Systematics

This species was originally described from Iraq and Pakistan. The type locality is unclear as the information given by Koumans (1955) gives more than one locality, as follows:-

"Habitat.-Mesopotamia, Karachi.
I have seen 2♂ and 2♀. These were from the following localities:-
                 Indian Museum Collection.
Fao estuary of the Shatt-el-Arab, Mesopotamia, ♀        H. J. Walton.
Karachi ♂ and ♀                                                          W. D. Cumming.
Mouth of Shatt-el-Arab ♂                                             W. T. Blanford.".

The type locality could be Fao and the holotype is the female specimen caught by H. J. Walton and named for him, the remainder being paratypes - by implication. Alternatively and probably correctly, these are all syntypes as no holotype was formally designated. The date of publication of Koumans work is 1955, not 1941 as cited by Murdy (1989).

This species has been confused with Periophthalmus koelreuteri (Pallas, 1770), itself a synonym of Periophthalmus barbarus (Linnaeus, 1766) according to Murdy (1989). P. barbarus does not occur in the Persian Gulf region. P. waltoni has been placed in the synonymy of P. koelreuteri in works on Persian Gulf fishes, e.g. by Relyea (1981), but the revision by Murdy (1989) is followed here. Another mudskipper species listed in Coad (1991b), Periophthalmus weberi Eggert, 1935, should be deleted from the list as Murdy (1989) does not report it from the Persian Gulf.

Two syntypes of Periophthalmus waltoni are in the Rijksmuseum van Natuurlijke Historie, Leiden (RMNH 17004) and 4 syntypes are in the Zoological Survey of India, Calcutta (possibly lost) (Murdy, 1989). However, this is more fish than listed in Koumans (1955).

Key characters

The pelvic fins are totally united into a sucker with a well-developed basal membrane or frenum (absent in P. barbarus). The anal fin base and second dorsal fin base are 27% or less of standard length and there are no canine teeth internal to the lower jaw symphysis in contrast to Boleophthalmus, the other mudskipper of southern Iran.

Morphology

First dorsal fin spines 10-14, second dorsal fin with 1 spine and 12-14 soft rays. Anal fin with 10-13 soft rays. Pectoral fin rays 13-15. Scales in lateral series 90-121, predorsal rows 27-37. The upper jaw has 4-5 anterior teeth on each side much larger than lateral teeth. Upper jaw teeth 19-28, lower jaw teeth 17-23. Gill rakers 9-16, mean 11, on each arch, triangular in shape with 3-4 spines at the top of each raker (Barak et al., 1994). The first dorsal fin lacks elongate spines and is slightly rounded. The dorsal fins are not connected by a membrane. The gut shortens with growth in terms of body length indicative of a carnivorous habit (Barak et al., 1994).

Sexual dimorphism

Females have a lozenge-shaped first dorsal fin (i.e. anterior 6 spines equal in height followed by abruptly shortened ones) with a height less than body depth; in males this fin equals body depth.

Colour

The overall colour is a light grey-brown. The flank bears blotches which, below the soft dorsal fin, take on the form of 8 short bars and there is a scattering of small silvery or white dots. Ventrally the spots form roughly transverse silvery stripes. The head top is also blotched and the sides bear a few small white dots. There are 7 irregular black blotches along the back. The first dorsal fin is dusky brown to light grey and its margin is yellowish between spines 1 to 8 and dark just below this except for the posteriormost 3-4 spines. There is a series of light spots on each interray membrane on the basal half of the fin. The second dorsal fin is dusky brown, with a pale margin, followed by a black stripe, and then with a white spot at the middle of each membrane thus forming a horizontal dotted line along the mid-fin. The caudal fin is a dusky brown, darker basally. There are 3 black blotches on the caudal peduncle. The pectoral fins are a light dusky brown on the rays with the membranes on the upper half pale with dark, brownish streaks in mid-fin, and a whitish margin is present. The pelvic fins are blackish with a reddish-brown or pale margin.

Size

Reaches 20.0 cm total length (Mhaisen and Al-Maliki, 1996).

Distribution

Found from the Persian Gulf to Pakistan. Reported from the Shatt al Arab, Iraq near Iranian Khuzestan by Khalaf (1961), Al-Nasiri and Hoda (1975b, 1976), Al-Hassan et al. (1989), and Hussain et al. (1989; 1997). Specimens believed to be this species have been reported from Iranian fresh waters but no specimens have been examined. Holly (1929b) records this species from the type locality of Barbus baschakirdi in the Bashakird Mountains (see Cyprinion watsoni). The Museum of Comparative Zoology, Harvard has a Periophthalmus species recorded from Manyuhi on the Shatt al Arab in irrigation ditches (MCZ 149602) but the identity of this specimen needs to be confirmed.

Abdoli (2000) maps this species from the Arvand River in the Tigris River basin, the lower Zohreh (= Hendijan), lower Helleh and Mand rivers in the Gulf basin, the Kul and Mehran rivers of the Hormozgan basin, and the lower reaches of rivers of the Makran from the Jagin to the Bahu Kalat.

Zoogeography

This species has ready access to the sea and can colonise rivers along the Iranian coast.

Habitat

The habitat and behaviour of this species is similar to Boleophthalmus dussumieri (q.v.; Tytler and Vaughan (1983) review behaviour of this species in Kuwait, their Periophthalmus koelreuteri being this species according to Murdy (1989)). However it favours areas of mud which are drier on the upper and middle regions of the shore. The burrow is Y-shaped with two entrances and a depth of 30 cm in mud. Fish occupy several burrow systems within a 2-3 m home range (Clayton and Snowden, 2000). Young first appear on mud flats in April but stay in wet mud or shallow pools. They move onto drier areas by May after some growth (1.5-2.5 cm). There are up to 30 fish per 100 sq m on Kuwait mud flats. The activity range of body temperatures is 14-20°C in January and 26-34.5°C in June. Body temperatures do not exceed 35°C even when air temperatures exceed 40°C because of evaporative cooling. In tidal pools of a few centimetres depth in the Khawr az Zubayr, water temperatures ranged from 16 to 44ºC, pH from 7.6 to 8.7, dissolved oxygen from 5.2 to 8.8 mg/l and salinity from 10.2 to 20.2‰ (Al-Daham and Al-Noor, 2000). Holes from 50 to 80 cm depth, with two openings separated by not more than 50 cm, are constructed as refuge from extreme temperatures, high winds and predators. The mud is carried to the outside of the hole in the fish's mouth, and forms a dam-like structure around the shelter not exceeding 8 cm in height. The fish spends most of the ebb tide outside the shelter.

As well as being found on mudflats of the sea shore, this mudskipper is found in the Shatt al Arab and other rivers of the Persian Gulf.

Age and growth

Abdoli et al. (2009) give length-weight parameters for fish from the northern Persian Gulf as a = 0.00002 and b = 2.86.

Barak et al. (1994) studied this species in the Khawr az Zubayr, Iraq and found growth to be allometric with the regression coefficient significantly (p<0.05) greater than 3. (W = 1.74x10^-4 L^2.35 (r = 0.99)). Al-Daham and Al-Noor (2000) found the smallest mature males were 7.3 cm and females 7.4 cm in the Khawr az Zubayr with maturity at age one year.

Food

Fiddler crabs are stalked as the main prey of this mudskipper in Kuwait (Tytler and Vaughan, 1983) but shrimps and other invertebrates are also taken. High wind speeds and surface temperatures below 15ºC inhibited hunting. Hunts were spatially well separated because of the long time period before crabs returned to the surface after a hunt in their vicinity (Clayton and Snowden, 2000). On the intertidal mudflats of Iraq at the head of the  Persian Gulf, this mudskipper feeds predominately on fish when larger than 90 mm (frequency 78.9%, occurrence 80.0%) with shrimps (14.1%, 20.0%), insects (3.2%, 10.0%), copepods 2.1%, 5.0%) and Daphnia sp. (1.7%, 5.0%). Fish smaller than 80 mm had values much lower for fish (6.7%, 8.3%) and higher for copepods (75.1%, 83.3%) with Daphnia sp. at 13.3% and 16.6%, insects at 2.7% and 4.1% and shrimps at 2.2% and 4.1%. Barak et al. (1994) found this species to be cannibalistic and piscivorous in the Khawr az Zubayr based on gill raker gap, gut-length/body length ratios decreasing with size, and stomach contents. Copepods were the major food item of smaller mudskippers (<70 mm) while mudskippers larger than this took fish. Mhaisen and Al-Maliki (1996) report food items as percentage of occurrence from fish caught in the Khawr az Zubayr estuary of Iraq to be 67.2% crustaceans (shrimps, crabs, barnacles and others), 34.5% snails, 3.4% insects and 1.7% fishes. Some fish consume plant material in winter months only, presumably in the absence of animal food.

Reproduction

Spawning in the marine environment of the Khawr az Zubayr takes place in March, the release of larvae being timed to take advantage of phytoplankton and zooplankton blooms (Hussain and Ahmed, 1999). Al-Daham and Al-Noor (2000) give the spawning period as March to April in the Khawr az Zubayr with a fecundity of 11,560-35,005 eggs for fish 7.4-12.9 cm long. A water temperature over 18ºC was the primary factor for spawning stimulation.

Parasites and predators

Mhaisen and Al-Maliki (1996) give information for Iraqi fish. E. Kahrom in the Crocodile Specialist Group Newsletter reports that muggers (marsh crocodile, Crocodylus palustris) eats a Periophthalmus in the Sarbaz River of Iranian Baluchestan (www.flmnh.ufl.edu/natsci/herpetology/newsletter/news173b.htm, downloaded 15 February 2002). However this may well be Boleophthalmus dussumieri.

Economic importance

None.

Conservation

No study of the numbers of this species in Iranian waters has been carried out so its status cannot be assessed.

Further work

The biology and population numbers of this species in Iran needs study.

Sources

The colour description is based on Kuronuma and Abe (1986).

Iranian material: None seen.

Comparative material: CMNFI 1985-0183, 2, 35.1-40.7 mm standard length, Iraq, Shatt al Arab (no other locality data); BM(NH) 1954.11.10:1-2, 2, 112.6-119.0 mm standard length, Iraq, Fao (29º58'N, 48º29'E); BM(NH) 1976.12.8:1-2, 76.1-84.1 mm standard length, Iraq, Basrah (30º30'N, 47º47'E); BM(NH) 1981.3.19:7-10, 4, 91.3-104.3 mm standard length, Kuwait mudflats (no other locality data).

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