A small, elongate, cylindrical fish with a rounded tail and small eyes. Maximum length 250 mm; usually <190 mm. The belly and lower sides are pale, usually orange-yellow to yellow-grey or cream, with the dorsal and upper sides being darker (greenish-brown) with dark spotting or mottling. The single, short-based dorsal fin is positioned about 1/2 way down the body, and a prominent black spot is present at the base of the tail. The females are more solidly built than the males, and the pectoral fin of females is rounder than the more triangular or square-cut fin of males. Five pairs of barbels surround the small downturned mouth. The mucous-covered body is very slippery, making it difficult to handle. When in the hand or out of water, it moves like an eel.
There is some uncertainty in the taxonomy of weatherloaches present in Australia (and the aquarium trade) with multiple species potentially present, hybridisation between species, and cryptic species also recently identified in Japan. Currently all weatherloaches in Australia are referred to as M. anguillicaudatus.
Oriental weatherloach is a benthic fish, native to eastern and central Asia. It is an important aquaculture species in China and is widely consumed with ‘superior nutritional values and excellent flavour’ reported. It was imported into Australia in the 1960s and became a popular aquarium fish. It was first detected as a breeding population in the wild in Australia in 1984 (Vic) and, its importation was banned in 1986.
Oriental weatherloach is commonly found in slow-flowing or still water with sand, mud or detritus substrates into which it can burrow to escape predation and/or hibernate. Its common name reflects its’ supposed ability to predict the weather, becoming restless with changing barometric pressure. The species occurs in a range of habitats, from degraded urban and rural streams and ponds to relatively pristine headwaters.
It can survive in hypoxic or anoxic environments such as drying billabongs by ‘gulping’ air and passing it through a highly vascularised hindgut. It is highly resistant to desiccation, and can survive in habitats with no surface water for extended periods of time (up to 81 days). There are confirmed reports of people ‘digging up’ fish, from dried billabongs or farm dams, with the species found in moist tunnels in the dried mud.
It is eurythermal, tolerates water temperatures of from just below freezing to 30°C and has been recorded in thermal springs up to 42°C. Individuals are mature at ~100 mm length and may live for up to 13 years.
Little is known of its spawning ecology in Australia but it is thought to spawn in late spring and summer. In Asia spawning occurs in summer, with multiple batches produced. Between 4,000–8,000 eggs of ~1.5 mm diameter are deposited per batch. Fish migrate from streams onto floodplains or rice paddies to spawn, probably in response to higher water temperatures in shallow floodplain habitats. The eggs are laid on freshwater plants or mud and hatch after 2–3 days.
A study in the mid-Murray found that the abundance of age 0 weatherloach was positively correlated to short-term inundation but negatively correlated to long-term inundation of floodplain wetlands. In Japan it has been found to be more active at night in summer, but in spring is more active during the day.
The species is a generalist omnivore and senses food using a combination of chemical and tactile cues. It takes sediment and detritus into its mouth, sorts prey, and ejects the remaining sediment through its gill openings. The diet contains freshwater and terrestrial insect larvae, rotifers, algae, gastropods, molluscs, microcrustaceans and detritus.
Little is known of its’ impacts, but significant dietary overlap has been recorded with the native Mountain galaxias. It may also be a predator of eggs and/or larvae of native species, particularly those such as galaxiids and gudgeons with demersal adhesive eggs. Oriental Weatherloach carry a range of parasites not previously recorded from Australia.
Laboratory experiments indicate that the species can significantly depress macroinvertebrate numbers, as well as increasing turbidity and nitrogen levels. It has been recorded in the stomachs of Macquarie perch, Murray cod and trout in the Canberra region.
Oriental weatherloach is native to Asia and have established feral populations in at least 10 countries other than Australia. In Australia, the species is now established in the ACT, NSW, Vic, and SA. Formerly present near Brisbane, that population has been successfully eradicated. It is still expanding its range in the Basin, with populations establishing in SA following flooding that ended the Millennium Drought.
It was first recorded in SA at Chowilla in 2011 but has since been recorded at numerous locations along >350km of the SA Murray River and associated wetlands. Flooding and high flows seem to provide a key means of downstream and lateral dispersal. There is some evidence from Hattah Lakes that the species actively moves towards inflowing water during pumping to fill lakes in spring. During the 2022–23 flooding in the Murray River, very high abundances were reported to be clogging irrigation filters in the SA Riverland and adjacent NSW/Vic Sunraysia district.
The ability to survive without water means the species can move overland to colonise nearby water bodies. Illegal use as live bait by anglers is thought to be a significant factor in its spread between drainage systems in south-eastern Australia, and releases for religious reasons are implicated in its spread elsewhere in the world.
A total of 74 individuals were recorded in the Sustainable Rivers Audit (2004–2013) from 6 river valleys (57 from the Murrumbidgee and Kiewa valleys) with 53 from lowland and 21 from upland elevational zones respectively. The MDB Fish Survey (2014/15–2021/22) recorded 10 individuals from 3 river valleys (Kiewa, Murrumbidgee, Loddon), but the species is undoubtedly more abundant in off-channel habitats and wetlands.
Beesley et al. 2014a; Dove & Ernst 1998; Fujimoto et al. 2008; Fredberg et al. 2014; Keller & Lake 2007; Koetsier & Urquhart 2012; Koster et al. 2002; Lintermans 2004; Lintermans & Burchmore 1996; Lintermans et al. 1988b, 1990a,b; McNeil & Closs 2007; Naruse & Oishi 1996; Okada et al. 2017; Raadik et al. 2005; Urquhart & Koetsier 2014a,b; Wegener & Suitor 2013; Wood & Brown 2016; Yi et al. 2019; You et al. 2009; M. Lintermans unpubl. data.
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