Threatened fishes of the world: Galaxiella munda McDowall, 1978 (Galaxiidae)

Abstract

Common name: Western mud minnow. Conservation status: Restricted (Australian Society for Fish Biology’s list of Australian threatened fishes). Identification: D 6–8, A 9–12, P 9–12, V 5–7, C 13–15, vertebrae 38–43, myomeres 41–43. Maximum size 58 mm TL. A small freshwater fish with a scaleless, elongate slender body and long straight gut reaching about 65–70% of the body length. Dorsal fin is posteriorly placed and originates posterior to the vertical that passes through the fifth anal ray, no adipose fin is present. Between June and October adults of this species are characterised by their coloration which consists of two olive-brown longitudinal bands separated by an orange stripe and a silver belly. The colored lateral stripe gradually dissipates to become a thin silver-white line after October and by January most fish are a fairly uniform light olive-brown in color. Drawing by Howard Gill. Distribution: G. munda is restricted to a small area in the south-western corner of Australia that extends from Albany in the east to Margaret River in the west, with an isolated population 350 km north at Gingin (McDowall & Frankenberg 1981, Allen 1989, Gill & Neira 1994). It is likely that the discontinuity in the distribution of this species represents the loss of suitable habitat caused by widespread urban and rural development in this region. Abundance: This species is rare throughout most of its distribution, but is occasionally locally abundant. Habitat and ecology: G. munda is typically found in small streams or shallow pools connected to streams (Pen et al. 1991). Water temperature ranges from 11.0–23.0° C. Terrestrial fauna (dipterans) and dipteran larvae and pupae are the main component of the diet in winter, spring and summer, while cladocerans and copepods form the most important component in autumn. The life cycle of G. munda typically lasts for just over one year (Pen et al. 1991). Reproduction: At the end of their first year of life females and males reach total lengths of 47 and 43 mm, respectively, at which time individuals attain sexual maturity and develop a breeding livery of two olivebrown longitudinal bands separated by an orange stripe. The mean GSIs of females rise from less than 2.0 in February to a maximum of 15.0 in August before falling sharply to less than 1.5 in November, the mean GSIs of males follow a similar trend. This species is a multiple spawner and breeds between July and October with a peak in activity in late August, a period when water temperatures and daylength have begun to rise. Threats: Habitat alteration and the introduction of exotic species pose the main threats to G. munda and also the three other species endemic to this region. Habitat alteration is likely to occur through, the construction of dams, groundwater extraction and also agricultural and forestry practices in the uppermost catchment (causing alterations to inflow, salinisation, siltation and eutrophication). It should be noted that the introduction of exotic fish species (Gambusia holbrooki, Perca fluviatilis, Onchorhynchus mykiss and Salmo trutta) and those species translocated from eastern Australia (Macquaria ambigua and Bidyanus bidyanus) has already occurred in many of the major catchments in the region. The combined effects of habitat alteration and introductions may explain the apparent loss of G. munda from the headwaters of Lefroy Brook. Thus, whereas Pen et al. (1991) reported viable populations of this species in these waters, an ongoing study has failed to record any G. munda in these streams (Morgan unpublished data). It is therefore pertinent that during several recent dry years the reservoir immediately above a major dam was the only upstream section of Lefroy Brook to retain water during summer and autumn. Furthermore, during these dry years, the piscivorous P. fluviatilis was introduced to the reservoir and is now well established in this reservoir and the headwater streams. Conservation recommendations: The most important conservation is the preservation of ‘natural’ flow regimes and suitable habitat in the small streams of south-western Australia, to ensure this buffer zones must be maintained in areas used for both farming and forestry, and further introductions of non-endemic species should be prohibited. Remarks: G. munda is one of only eight species of freshwater fish that are endemic to south-western Australia.