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| Pseudomugil tenellus - photo© Dave Wilson |
Taylor, 1964
Delicate Blue-eye
Pseudomugil tenellus have a moderately compressed and elongated body; growing to a length of around 4-5 cm. Body colouration is translucent golden above the mid-lateral line and yellow with silver sheen below. The mid-lateral line consists of a series of discontinuous silvery spots becoming larger in older fish. The outer margins of the second dorsal and anal fins are light yellow. Females are similarly coloured but not as intense, and have much smaller uncoloured rounded fins. The differences in colour of the body and especially fins make the sexes of Pseudomugil tenellus easily distinguishable. The larger size of the fins in males, especially the second dorsal and the anal, make the distinction unequivocal.
Distribution & Habitat
Pseudomugil tenellus was first collected in 1948 by R. Miller from Oenpelli in Arnhem Land, Northern Territory. Miller reported that they were abundant in large billabongs and creeks below escarpment waterfalls in the Oenpelli area. However, they were not scientifically described until 1964. They have patchy distribution throughout the northern areas of the Northern Territory, around the Gulf of Carpentaria to Cape York Peninsula in Queensland. In New Guinea they have been found in the Bensbach River, though I suspect that their distribution in southern New Guinea will be much wider. It is also found in the Aru Islands. They have been recorded from catchments of the Alligator, Daly and Mary River systems in the Northern Territory, where they are commonly found in riverine floodplain billabongs. They have also been collected from Leanyer Swamp, a tidal swamp north-east of Darwin; Rapid Creek and a number of other streams in the Darwin region. In Queensland they have been collected in the Coleman, Edward, Jardine, and Watson Rivers; Jacky Jacky and Scrubby Creek (near Coen).
In summary, this species is commonly found in coastal brackish streams, freshwater floodplain billabongs and in some lowland backflow billabongs and perennial streams, usually not found very far inland. They are generally found in marshy swamps with dense aquatic vegetation and slow-flowing streams with mud, sand, or gravel bottoms. They have been found in the greatest number of sites during the mid-wet season. Usually where there is an abundance of aquatic vegetation. Water temperatures from 27° to 38°C; Dissolved Oxygen 5.0 to 7.8 mg/L; pH from 5.0 to 7.1; Conductivity 6 to 120 µS/cm.
Biology
Pseudomugil tenellus is an egg-scatterer, generally spawning amongst aquatic plants and grasses. Spawning may be aseasonal, with peaks of activity during the early-wet season. Ovaries examined contained 33-45 eggs, with a mean oocyte diameter of 1.0 mm. Eggs adhere to water plants and hatching occurs around 5-7 days at a temperature of 25° Celsius. Length at first maturity for females is around 18-24 mm and 23 mm for males.
The main dietary items of Pseudomugil tenellus were found to be algae, microcrustaceans and aquatic insects. The identifiable algae were green filamentous and blue-green algae and dinoflagellates. The microcrustaceans were mainly cladocerans, ostracods and copepods. Chironomid larvae were the main aquatic insects eaten. Other food items found in the stomachs were terrestrial insects and detritus. One study found that the diet in the late-dry season was mainly based on detritus (with associated unidentified organic material) and small quantities of chironomid larvae and pupae, and algae; no microcrustaceans were eaten. In the early-wet microcrustaceans appeared in the diet and detritus decreased in importance; aquatic insects also appeared in the diet during this season. In the mid-wet season Pseudomugil tenellus ate mainly microcrustaceans (particularly cladocerans) with smaller amounts of terrestrial and aquatic insects. By the late-wet-early-dry season algae were the main component of the diet.
© Copyright Adrian R. Tappin
Updated July, 2007.
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