Oxleyan pygmy perch - Nannoperca oxleyana
By Chris Thompson, Angela Arthington and Mark Kennard
Threatened Fish Profile – In Newsletter 30_1, May 2000
Drawing by Brad Pusey
Taxonomic affinities: The Australian pygmy perches comprise six species currently in two genera: Nannoperca and Nannatherina. A third genus, Edelia, was previously recognised but has been combined into Nannoperca. Although previously thought to belong to the family Kuhliidae or comprise their own family Nannopercidae, recent genetic evidence suggests that the pygmy perches belong within the Percicthyidae (P. Unmack, pers. comm.). Only one species of pygmy perch occurs in Queensland, Nannoperca oxleyana. This is the most northerly occurring species of the Nannopercids and a disjunct member of the genus (Johnson 1984, Kuiter & Allen 1985, Paxton et al. 1989, Kuiter et al. 1996).
Description: Dorsal fins VI-VIII,7-9(VII8). Anal fins III,7-9(8). Pectoral fins 11-13(12). Mid lateral scales 26-28. Transverse scales 11-12. Gill rakers on first arch 9-12.
A small (max. 50 mm, common to 35 mm) moderately compressed fish, body covered by ctenoid scales, lateral line absent and caudal fin truncate. Individuals of N. oxleyana are light brown to olive, darker on back, sides paler and mottled with 3 to 4 patchy dark brown bars extending from head to tail. Opercular flap has a blue iridescence. Scales with dusky outlines. Prominent round black spot with orange margin at the base of caudal fin, fins mainly clear. During breeding, dorsal and anal fins are black, caudal fin and lateral stripes scarlet (Merrick & Schmida 1984, Allen 1989, Kuiter & Allen 1985, Arthington & Marshall 1996, Kuiter et al. 1996).
Distribution and abundance: A restricted and patchy distribution in coastal lowland wallum ecosystems of south-eastern Queensland and northern New South Wales. Has been recorded from swamps, streams and lakes from the Richmond River, NSW, north to Tin Can Bay area in Qld and the sand dune islands of Fraser, Moreton and Stradbroke. Recent surveys in northern NSW identified a new population in a lake in Bundjalung National Park (Arthington 1996) and in a small drainage adjacent to Bundjalung National Park (Walker & Walker 1999, J. Knight pers. comm.). However, these surveys, failed to locate N. oxleyana from Lake Hiawatha, a previously known location while their status in the Richmond River remains unknown. Queensland mainland locations include Blue Gum Creek near the Glasshouse Mountains, Marcus Creek, Noosa River and its tributaries, Searys Creek, Carland Creek and Coondoo/Tinana Creek, a tributary of the Mary River. Recently only been recorded from Rocky and Coongul Creeks on Fraser Island though has previously been recorded from Woralie and Bogimbah Creeks. On Moreton Island, populations are present in Lake Jabiru, Spitfire Creek, North and South Warrajamba Creek, Blue Lagoon and North Eagers Creek on the eastern coast and in Ben Ewa Swamp and associated streams including Craven Creek and Tempest Creek on the western coast. On North Stradbroke Island, a small population of N. oxleyana is located in 18 Mile Swamp and there are unconfirmed reports of populations in waterbodies in the southern part of the island (Leggett 1990, Wager 1992, Arthington 1996, Arthington & Marshall 1993, Kuiter et al. 1996). Genetic analysis of N. oxleyana populations in south-eastern Queensland revealed relatively high levels of allozyme and mitochondrial DNA variation among discrete populations, suggesting that dispersal among populations is extremely limited (Hughes et al. 1999).
The distribution of N. oxleyana is shared with the Vulnerable honey blue-eye, Pseudomugil mellis, and the restricted ornate sunfish, Rhadinocentrus ornatus. N. oxleyana is generally not locally abundant although populations within Spitfire, Tempest, Marcus and Coondoo Creek comprised approximately 20% or more of the fish collected by electrofishing, seine netting and bait trapping (Arthington 1996).
Habitat and ecology: Found in lotic and lentic habitats of close proximity to the coast in wallum ecosystems. Habitats range from low conductivity (<250us cm-1), clear waters of pH 6 to 6.5, to darkly stained dystrophic waters of pH 4.2 to 6, over siliceous sand. Often found in close association with dense emergent and submerged marginal vegetation, leaf litter beds, and occasionally woody debris if present. Individuals in southeastern Queensland waters frequently use low flow environments (generally < 0.1m sec-1), in moderate water depths (up to 1.5m) and throughout the lower 2/3 of the water column (Arthington & Marshall 1993, Arthington 1996, Kennard unpublished data). Snorkeling observations in Spitfire Creek suggest that N. oxleyana is highly mobile, moving as individuals, pairs and in groups of three or four younger individuals while foraging along the stems of aquatic plants (Arthington 1996). The extent of these daily foraging movements is unknown. Available dietary data (178 individuals from the Noosa River and Spitfire Creek, Moreton Island) indicate that N. oxleyana is a microphagic carnivore. The total mean diet was composed primarily of zooplankton (31%), aquatic insects (23%) and atyid shrimps (22%) with smaller contributions of terrestrial arthropods (3%) and aerial forms of aquatic insects (2%) (Arthington & Marshall 1993, Arthington 1996). N. oxleyana has an extended breeding season from spring through to autumn but spawning is concentrated in October to December and is probably stimulated by increasing water temperatures (minimum temperature 20 oC). Courtship and mating involve a pair casually approaching each other and as they near, quickly shuddering and releasing eggs and milt (Wager 1992). Spawning is protracted with a few eggs laid daily over several days. Eggs are demersal and adhesive, attaching to aquatic vegetation or the substrate depending on where mating occurred. Young hatch in three to four days and commence foraging in another day or two. Aquarium bred fish mature in four to five months (Wager 1992, Arthington & Marshall 1996, Kuiter et al. 1996).
Conservation status and threats: Currently listed as Endangered (Australian Society for Fish Biology - Conservation Status of Australian Fishes, 1999 listing; ANZECC Threatened Fauna List, 1999). The primary threats to N. oxleyana include loss of habitat due to residential housing development and road construction, expansion of exotic pine plantations by forestry, and water pollution associated with mining operations and agriculture (Leggett, 1990, Arthington & Marshall 1993, 1996, Wager & Jackson 1993, Arthington 1996). N. oxleyana may also be impacted by introduced species such as Gambusia holbrooki.
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Arthington, A. H. (1996). Recovery plan for the Oxleyan pygmy perch Nannoperca oxleyana. Final report to the Australian Nature Conservation Agency. 129pp.
Arthington, A. H. & Marshall, C. J. (1993). Distribution, ecology and conservation of the honey blue-eye, Pseudomugil mellis, in south-eastern Queensland. Final Report to the Australian Nature Conservation Agency Endangered Species Program. Volume 1.
Arthington, A. H. & Marshall, C. J. (1996). Threatened fishes of the world: Nannoperca oxleyana Whitley, 1940 (Nannopercidae). Env. Biol. Fish. 46: 150.
Australian Society for Fish Biology (1999). Conservation Status of Australian Fishes - 1999. ASFB Newsletter. 29: 34-37.
Australian and New Zealand Environment and Conservation Council (ANZECC) (1999). Threatened Australian Fauna. 16pp.
Leggett, R. (1990). A fish in danger - Nannoperca oxleyana. Fishes of Sahul. 6 (1): 247-249.
Wager, R. (1992). The oxleyan pygmy perch: maintaining breeding populations. Fishes of Sahul. 7(2): 310-312.
Walker, G. & Walker, D. (1999). A fortunate discovery - Oxleyan pygmy perch. ANGFA Bulletin. 45:16.