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Blackstriped Dwarf Galaxias (Galaxiella nigrostriata)

A small, endangered freshwater fish confined to acidic, temporary peat wetlands and black-water pools in south-western Western Australia. It aestivates in moist subsurface peat or sandy soils when wetlands dry, so clearing, groundwater change, sedimentation and altered wetland hydrology can affect fish that are not visible during site inspections.

Conservation status

Commonwealth, EPBC Act 1999: Endangered.

Western Australia, Biodiversity Conservation Act 2016: Endangered.

Breeding season

Timing varies between the main southern range and northern outlier populations. The table describes the general pattern supported by the supplied records, with later emergence and breeding documented at the Melaleuca Park outlier.

Seasonal timing is indicative. Confirm local inundation, emergence and breeding timing before works, especially for northern outlier populations where emergence and spawning may be delayed.

  • Aestivation and dry-season refuge: Fish aestivate in moist subsurface peat or sandy soils during dry summer and autumn. The exact onset and duration depend on wetland drying.
  • Breeding: Breeding peaks in late autumn and early winter. June is reported for southern populations, while breeding at the northern EPP 173 population was delayed.
  • Young: Young fish were recorded from August and September at EPP 173. Juvenile growth occurs in seasonal surface water before later aestivation.
  • Seasonal emergence: Fish emerge after winter rainfall and wetland filling. At EPP 173, adults were first recorded in late June after the wetland refilled.
  • Highest clearing risk: Dry summer and autumn are the highest risk period for ground disturbance because fish may be aestivating below the wetland surface and cannot be detected by ordinary aquatic surveys. Clearing during breeding and juvenile periods also risks direct loss of adults, eggs or young.

Identification

The Blackstriped Dwarf Galaxias is a very small galaxiid that usually occurs in shallow, acidic, dark-water wetlands. It may be absent from surface water during the dry period because individuals aestivate below the wetland bed.

Adults reach approximately 4 cm in length. The body develops a bright yellow-orange lateral stripe bordered by black stripes during the late autumn and early winter breeding period.

The species is associated with acidic, black-water temporary pools and peat wetlands. Water is often dark from tannins, and fish may shelter near the cooler bottom water where strong thermal stratification develops.

Identification: Distinguishing it from similar fish

Do not rely on a single visual feature when identifying small galaxiids. The morphologically similar Western Mud Minnow, Galaxiella munda, is usually found further inland in smaller creeks and pools, although the two species can overlap in floodplain wetlands with seasonal connections to more permanent water.

The Blackstriped Dwarf Galaxias is commonly associated with ephemeral coastal floodplain and peat-flat wetlands. It may occur with the Western Minnow, Western Pygmy Perch and Salamanderfish, but those species require separate identification.

Identification: Field signs and survey cautions

There are no documented tracks, scats, calls, nests, hollows or eyeshine associated with this fish. The main field sign is the presence of suitable acidic, temporary wetland habitat, followed by live fish detected in surface water.

During the dry period, fish may be below ground in moist peat or sandy substrate. A negative aquatic survey during dry conditions should not be treated as proof that the wetland is unoccupied.

Fish can be highly sensitive to heat. In one northern population, individuals avoided water warmer than approximately 26 degrees Celsius when cooler bottom water was available.

Distribution: State and regional range

The species is endemic to south-western Western Australia. Its main distribution is in the lower south-west, with disjunct northern populations on or near the Swan Coastal Plain.

The species is known only from Western Australia. The main range is a narrow coastal and near-coastal strip of peat flats extending broadly between Augusta and Albany, including wetlands near the lower south coast.

Northern outlier populations have been recorded near Bunbury and at Melaleuca Park near Perth. The Melaleuca Park population is approximately 350 km north of the main southern distribution and occurs in a wetland designated EPP 173.

Distribution: Subpopulations and local records

The Melaleuca Park population is an important northern outlier associated with a spring-fed, temporary black-water wetland. The wetland is approximately 1.5 ha, reaches a maximum depth of about 70 cm and has a permanent spring seepage area that can retain shallow water when nearby wetlands are dry.

For the Morley Ellenbrook rail project, four wetlands within or adjacent to the development envelope were assessed as potential habitat. The proposed footprint intersected parts of two wetlands, UFI 8678 and UFI 15259. The closest known occurrence was approximately 12 km north of that development envelope, and targeted August 2020 surveys detected no individuals.

Distribution: Population size and trend

The supplied documents do not provide a reliable estimate of the total number of individuals or the number of occupied populations. The species has a restricted distribution and its habitat has declined through wetland loss, groundwater change, urban expansion and a drying climate.

Small or isolated populations should be treated as significant during project planning because the species can be locally resident and may not recolonise a wetland from an adjacent waterbody each year.

Conservation status: EPBC Act Endangered; Western Australia Endangered.

Known northern outlier separation: Approximately 350 km north of the main southern distribution.

Closest known occurrence in one assessed project area: Approximately 12 km north of the development envelope.

Habitat: Wetland types

Blackstriped Dwarf Galaxias habitat is defined by water regime and water chemistry as much as by vegetation. Suitable sites are generally acidic, tannin-stained, temporary wetlands with peat or sandy substrates and reliable seasonal inundation.

The species occurs in acidic ephemeral peat wetlands, temporary black-water pools, peat flats and associated shallow wetland margins. It can occupy wetland beds that dry during summer and autumn and refill after winter rainfall.

Known habitat may include spring-fed areas that retain shallow water after surrounding wetlands have dried. At EPP 173, the spring seepage maintained boggy peat and shallow water less than 11 cm deep in late summer and autumn.

Habitat: Water, substrate and structure

Suitable habitat generally has shallow groundwater, sandy or peat soils, dark tannin-stained water and low salinity. At EPP 173, the water was very dark, with colour exceeding 1,200 TCU, and salinity was low at approximately 444 microsiemens per centimetre.

The species needs moist substrate that remains suitable for aestivation when surface water disappears. Spring seepage, wetland vegetation, peat beds and surrounding vegetation that limit wind mixing can help maintain cool water refuges.

Habitat: Climate and elevation limits

The species is associated with the Mediterranean climate of south-western Australia, where wetlands fill during wetter months and may dry during summer and autumn. The supplied documents do not define a national elevation range.

The northern outlier at Melaleuca Park experiences hotter and drier conditions than the main southern range. At that site, average summer maximum temperature was reported as approximately 31 degrees Celsius, compared with approximately 25 degrees Celsius in the southern distribution.

Foraging habitat: Diet

The species feeds within shallow temporary wetlands and associated water layers. Its diet is mainly small aquatic invertebrates, with some terrestrial insects taken from the water surface.

Recorded prey includes microcrustaceans, dipterans and rotifers. More detailed stomach analyses recorded cladocerans, rotifers, harpacticoid copepods, calanoid copepods, mites, diatoms and terrestrial insects.

The relative importance of surface prey varies between sites and seasons. At EPP 173, terrestrial insects formed a smaller part of the diet than in southern populations.

Foraging habitat: Foraging conditions

Fish forage through the water column, including near the bottom and at the surface. In strongly stratified water, they remain near cooler bottom water and make short movements to the surface to take prey before returning to depth.

The species requires wetland water that persists long enough to support aquatic invertebrate prey. Loss of inundation, excessive warming, reduced groundwater seepage or altered water chemistry can reduce feeding habitat even where the wetland bed remains physically intact.

Foraging habitat: Foraging range

The supplied documents do not provide a measured daily foraging range. Individuals at EPP 173 were considered locally resident within the wetland beds, rather than dependent on annual recolonisation through the outflow channel.

Breeding habitat: Breeding biology

Breeding occurs in seasonally inundated acidic wetlands. Breeding habitat needs sufficient water depth and duration for spawning, egg development and juvenile growth before the wetland dries.

Adults can breed during the late autumn and early winter period. Spawning in southern populations has been reported from June, while the northern EPP 173 population began later, with adults first recorded in late June and young fish sampled from August.

The supplied documents do not provide a confirmed clutch size, gestation period, lifespan beyond the approximately 12-month life cycle, or a precise age at first breeding. Adults of breeding age belong to the one-year class, and individuals generally die shortly after breeding.

Breeding season: Late autumn to early winter, broadly May to July; June is reported for southern populations and breeding was delayed at EPP 173.

Egg or clutch size: Not stated in the supplied documents.

Gestation or incubation: Not applicable for this fish and not stated as an egg-development period in the supplied documents.

Age at maturity: Breeding-age fish are in the one-year class; a more precise age is not stated.

Lifespan: Approximately 12 months; adults generally die after breeding.

Breeding habitat: Breeding habitat features

Suitable breeding habitat includes shallow, acidic, temporary pools and wetland margins with emergent vegetation, peat or sandy substrates and enough seasonal water retention for larvae and juveniles.

Groundwater seepage can extend the period of inundation. At EPP 173, cool spring water supported a small area of wet peat and shallow water during the period when nearby wetlands were dry.

Sheltering habitat: Aestivation refuge

The main non-breeding refuge is the moist substrate of the wetland bed. Fish may be difficult to detect because they aestivate below ground during dry summer and autumn conditions.

During drying, individuals burrow into moist subsurface peat or sandy soil and aestivate until suitable surface water returns. This refuge can be within the wetland bed rather than in a permanent pool or downstream channel.

At EPP 173, fish were considered locally resident within the swamp beds. No fish were caught in the downstream outflow during the study, and fish remained in an auxiliary wetland when it was isolated from the main wetland.

Sheltering habitat: Water-column refuge

When surface water becomes hot, dark tannin-stained water can develop strong thermal stratification. Cooler bottom water then provides a refuge from damaging surface temperatures.

At EPP 173, fish selected water at approximately 14.5 degrees Celsius near the bottom when a thermal gradient was available. Fish did not tolerate temperatures above approximately 26 degrees Celsius for more than a few seconds in laboratory observations.

Sheltering habitat: Site protection measures

Maintain wetland beds, peat and sandy substrates, spring seepage, surrounding vegetation and buffer areas. Avoid soil compaction, drainage, excavation and activities that remove the dark-water conditions or groundwater inputs that support cool refuges.

During dry-season works, assume that suitable moist substrate may contain aestivating fish even when no surface water is present.

Threats: Clearing and wetland disturbance

The species has a restricted range and depends on wetland water regimes that are easily altered by development. Project risks can affect both occupied surface water and aestivating fish in the wetland substrate.

Direct clearing of temporary wetlands, peat beds and wetland margins can remove breeding, feeding and aestivation habitat. Excavation, filling, compaction and vehicle access can damage fish sheltering below the surface during dry conditions.

The Morley Ellenbrook assessment identified potential habitat in four wetlands and proposed clearing of 0.5 ha of one wetland and 0.6 ha of another. Such impacts should be avoided where possible, including indirect loss of wetland function outside the construction footprint.

Threats: Hydrology and groundwater change

Groundwater extraction, lowered water tables, altered surface flows, drainage and changes to spring seepage can shorten inundation periods or remove the moist substrate needed for aestivation.

Maintain natural inflows, groundwater levels and wetland water regimes. Assess changes to both surface water and groundwater because a wetland can remain physically present while becoming unsuitable for the species.

Threats: Water quality and sediment

Construction can increase sedimentation and turbidity and can alter water quality through acid sulfate soil disturbance, nutrient pollution or contaminant spills.

Use controls that prevent dirty water, concrete washout, fuel, chemicals and sediment from entering wetlands, spring seepages or connecting drainage lines. Acid sulfate soil management is particularly relevant where wetland soils are excavated or dewatered.

Threats: Climate, heat and fire-related change

Reduced rainfall, hotter conditions and climate-driven wetland drying can reduce the number and area of occupied sites. Warmer water can also remove the cool bottom-water refuge used by fish in northern outlier wetlands.

Fire protection works and artificial water points may alter wetland substrates, vegetation and water chemistry. Any proposed water point or wetland modification should be assessed for both fire-management objectives and fish habitat.

Threats: Predators, invasive fish and fragmentation

The conservation advice identifies introduced invasive fish as a threat. Stocking, accidental transfer of fish and connection to permanent waterbodies can increase predation or competition.

Urban expansion, roads and infrastructure can fragment wetlands, remove vegetation buffers and increase the risk of altered drainage and groundwater extraction. The supplied documents do not identify a species-specific road mortality rate, but road construction near wetlands can cause direct habitat loss, sediment inputs and hydrological change.

Survey methodology: 1. Targeted aquatic survey

Survey the Blackstriped Dwarf Galaxias in acidic, temporary wetlands and associated peat substrates. The species is small, seasonal and difficult to detect when wetlands are dry, so surveys must be timed to inundation and breeding activity.

Survey during the wet period, after winter rainfall has inundated the wetland and before water levels fall substantially.

Use targeted fish survey methods suited to shallow, acidic wetlands, such as fine-mesh dip-netting, seine-netting or other approved aquatic sampling methods. The supplied project survey used a targeted survey in August 2020, which was considered the most appropriate survey period, and applied methods exceeding those in the conservation advice.

Sample all suitable wetland habitat within the proposed disturbance area and adjacent wetlands that could be affected by changed surface water or groundwater flows.

Record survey conditions, water depth, pH, water temperature, water permanence, substrate, aquatic and emergent vegetation, and the location and area of each sampling site.

Do not assume that suitable habitat is occupied only because fish are not captured. The 2020 survey found suitable habitat at all sites but detected no individuals.

Most suitable survey period recorded: August, during the wet period

Project example: A targeted survey was completed in August 2020, with no individuals detected

Known habitat setting: Acidic, temporary peat wetlands and black-water pools

Survey methodology: 2. Survey the wetland and dry-season refuge

Inspect the wetland bed, peat margins and shallow seepage areas for signs of suitable habitat when water is present.

When the wetland is dry, inspect moist peat, sandy peat and root mats for aestivating fish only where this can be done without damaging the substrate.

Use a staged and low-impact search method, with the aquatic ecologist deciding whether any substrate excavation or sieving is justified and authorised.

Give particular attention to groundwater-fed seepage areas, shallow water and wet peat that can remain moist after surrounding wetland areas have dried.

Aestivation: The species survives dry periods by aestivating in moist subsurface substrates

Example wetland conditions: EPP 173 retained shallow water over boggy peat in late summer and autumn because of permanent spring seepage

Survey methodology: 3. Record habitat and detection constraints

Map each wetland, seepage area, peat margin and proposed impact area using accurate coordinates and a consistent wetland identifier.

Record whether the wetland is ephemeral, the extent of open water, water depth and evidence of groundwater input.

Record water colour and temperature where practical, because dark, thermally stratified water can provide cooler refuge from high surface temperatures.

Avoid sampling during unusually hot conditions where fish may be confined to cooler bottom water and may be harmed by lifting them through warm surface water.

Use appropriate animal ethics, collection and state permit conditions for all capture, handling and release activities.

Thermal tolerance recorded: Laboratory fish could not tolerate temperatures above 26°C for more than a few seconds

Preferred temperature recorded: Approximately 14.5°C

Example water chemistry: EPP 173 ranged from pH 5.5 when inundated to pH 3.25 to 3.8 during drying

Survey methodology: Minimum effort and reporting

  • Use the current Australian Government species survey guidance and any relevant Western Australian guidance when setting the final survey design; no dedicated survey guideline is included in the supplied documents.
  • Document the survey dates, rainfall and hydrological conditions, methods, sampling locations, effort, water quality, habitat condition, results and limitations.
  • Treat a non-detection as inconclusive where suitable habitat was present, the wetland was dry, access was incomplete or conditions were unsuitable for detection.
  • Submit confirmed records, negative survey results where requested, and accurate location data to the relevant state wildlife database and provide records to the Australian Government species information system where required.
  • Retain voucher, photographic or expert verification material for any suspected Blackstriped Dwarf Galaxias record.
  • Record the species under the accepted name Galaxiella nigrostriata and note the alternative common name Black-striped Minnow used in some approval documents.

Before habitat disturbance: Avoid and minimise habitat loss

Treat every suitable acidic, temporary wetland within or near the works as potentially important habitat. The closest known occurrence in the Morley Ellenbrook project material was about 12 km north of the development envelope, but suitable habitat was identified within and beside the envelope.

  • Avoid clearing wetlands, peat beds, shallow seepage areas and groundwater-dependent margins wherever practicable.
  • Retain the wetland hydrology, groundwater connection, dark-water conditions and vegetation buffer that support cool refuges and moist aestivation substrate.
  • Maintain surface and groundwater flows to retained wetlands and prevent barriers that isolate wetlands or alter seasonal inundation.
  • Retain connected wetland and peat habitat between occupied or potentially occupied areas, particularly where wetlands are seasonally connected.
  • Design drainage, culverts, roads and construction pads so they do not lower the water table, divert inflows, concentrate runoff or cause prolonged sedimentation.

Before habitat disturbance: Approvals and planning

EPBC listing: Endangered

Western Australian listing: Endangered

Project habitat identified in: Four wetlands within or adjacent to the development envelope had potential habitat; the footprint intercepted parts of two

  • Check whether the action may significantly affect the EPBC Act listed species and refer the action if required under the EPBC Act.
  • Obtain all relevant state approvals, wildlife permits, aquatic fauna collection permits and animal ethics approvals before survey, capture, handling or relocation.
  • Prepare a fauna and wetland management plan that identifies no-go areas, wetland buffers, hydrology controls, survey timing, stop-work triggers and response contacts.
  • Schedule disturbance outside the period when wetlands are inundated and fish are breeding or actively using shallow water, where this is consistent with the approved action and cannot increase risks to aestivating fish.
  • Stage works so that retained wetlands remain protected while each work area is surveyed, cleared and checked.

Before habitat disturbance: Prepare and mark the site

  • Complete the targeted wetland survey before ground disturbance and update the impact map with any confirmed records and all suitable habitat.
  • Clearly mark wetland exclusion areas, peat margins, seepage zones, retained vegetation and access routes before machinery enters the site.
  • Install exclusion fencing where it can prevent machinery, vehicles and stockpiled material entering wetland habitat without diverting water into or away from the wetland.
  • Keep fuels, chemicals, spoil, concrete washout, sediment controls and waste outside wetlands and their drainage paths.
  • Brief the supervisor, machine operators and fauna spotter catcher on the species, its habitat, dry-season aestivation risk and the stop-work procedure.

During habitat disturbance: Daily controls and supervision

The main construction risks are direct loss of wetland and peat habitat, altered hydrology, sediment and turbidity, acid sulfate soil impacts and contamination. Controls must remain active while machinery is operating, not only during initial clearing.

  • Have the fauna spotter catcher inspect the approved work area each day before machinery starts and after rainfall, flooding or any unplanned water movement.
  • Keep machinery, vehicles and workers within the approved footprint and maintain exclusion fencing and wetland buffers.
  • Maintain sediment, erosion, acid sulfate soil, spill and dewatering controls throughout the shift.
  • Prevent turbid water, contaminated runoff, concrete washout and fuel or chemical spills from entering wetlands, seepage areas or drainage lines.
  • Stop work and notify the environmental officer if the approved footprint, wetland buffer or hydrological control is breached.

During habitat disturbance: Fauna spotter catcher response

  • The fauna spotter catcher must not enter or disturb wet peat or aquatic habitat without the required authorisation and a safe work method.
  • If a fish is found, stop the relevant activity, keep the animal in water from the same wetland where practicable, and contact the authorised aquatic ecologist or fauna handler.
  • Do not handle, transport or relocate the fish unless the person is authorised under the relevant permit and the relocation method has been approved.
  • If relocation is authorised, use nearby retained habitat with suitable water quality, hydrology and substrate, and record the source and release locations.
  • Send injured or distressed animals to an appropriately qualified aquatic veterinarian or wildlife carer through the approved project procedure.

During habitat disturbance: Wetland and habitat feature handling

  • Do not excavate, compact, drain or stockpile material on peat beds, wetland margins or moist aestivation habitat unless the action is approved and supervised.
  • Treat groundwater seepage, shallow water and moist subsurface peat as habitat features requiring protection during dry-season works.
  • Manage acid sulfate soils under the approved plan because changes in water quality can affect surrounding wetlands.
  • Use the approved hydrology controls to prevent changes to surface and groundwater flows, sedimentation, turbidity and contamination.
  • Apply a stop-work trigger for any confirmed Blackstriped Dwarf Galaxias, unexpected wetland connection, uncontrolled dewatering, fish mortality or visible pollution entering habitat.

During habitat disturbance: Records and incident reporting

  • Record daily checks, work areas, weather, hydrological conditions, fauna observations, captures, handling, relocations, injuries, deaths, releases and control failures.
  • Photograph and map any animal record and describe the wetland condition and exact location.
  • Report any confirmed occurrence, mortality, unapproved impact or failure of a condition to the project environmental officer and the relevant regulator within the timeframe in the approval.
  • Review the work method before restarting after a stop-work event.

After habitat disturbance: Post-clearance checks

Post-clearance work must confirm that no fish or suitable wetland habitat was missed and that retained wetlands still receive the water and protection they need.

  • Inspect the cleared area, wetland margins, drainage controls and retained peat habitat after each work stage and after major rainfall.
  • Complete additional targeted aquatic checks if water returns to a disturbed or dewatered area, if fish are observed, or if works changed groundwater or surface water movement.
  • Check that exclusion fencing, sediment controls, spill controls and wetland buffers remain intact until the site is stable and the approval allows their removal.
  • Repair erosion, compaction, drainage faults and sediment releases immediately where they threaten retained habitat.

After habitat disturbance: Monitoring and compliance reporting

  • Monitor water levels, groundwater-dependent seepage, turbidity, pH, temperature and wetland condition at retained and potentially affected wetlands using the approved monitoring plan.
  • Compare monitoring results with pre-works conditions and the project approval limits, and investigate any loss of inundation, increased salinity, changed pH or persistent turbidity.
  • Report survey results, incidents, mitigation performance, confirmed records and any residual impact to the relevant regulators and wildlife databases.
  • Use the monitoring results to adjust drainage, dewatering, sediment, weed and access controls before the next construction stage.

After habitat disturbance: Residual impacts and offsets

  • Reassess the need for offsets if the action causes a residual significant impact after avoidance and mitigation.
  • Do not treat a non-detection during pre-clearance survey as evidence that habitat has no conservation value.
  • Document the basis for any conclusion that no residual significant impact remains, including survey limitations and hydrological effects.

Rehabilitation actions: Restore wetland structure and hydrology

Rehabilitation should restore the wetland processes that allow this species to breed in shallow acidic water and survive dry periods in moist peat. Planting alone will not replace lost groundwater, inundation or peat habitat.

  • Reinstate natural wetland contours, shallow depressions, peat surfaces and seasonal flow paths where these were disturbed.
  • Restore groundwater and surface water connections without creating permanent open water, rapid drainage or concentrated inflows that change the wetland regime.
  • Remove compacted pads, temporary crossings and spoil that prevent infiltration, seepage or seasonal inundation.
  • Use local wetland and peatland plant species appropriate to the site, and retain or re-establish vegetation that shades water and helps maintain cool conditions.
  • Do not introduce fish, aquatic plants, soil or water from another catchment.

Rehabilitation actions: Protect dry-season refuge habitat

  • Retain moist peat, sandy peat, root mats and seepage areas as no-go areas during dry periods.
  • Avoid disturbing wetland substrates when fish may be aestivating below the surface.
  • Control weeds and prevent machinery movement through wetland buffers so that peat structure and groundwater input are maintained.
  • Manage fire, access and fuel loads in accordance with the approved wetland management plan, avoiding actions that dry, expose or destabilise peat.

Rehabilitation actions: Water quality, predators and monitoring

Habitat condition to restore: Acidic, temporary, often dark-water wetlands with shallow water and moist subsurface peat

Temperature consideration: Cool groundwater and thermal stratification can provide refuge from surface temperatures above 26°C

  • Maintain sediment, acid sulfate soil, nutrient, spill and wastewater controls until monitoring shows that rehabilitated wetlands are stable.
  • Prevent introduced or invasive predatory fish from entering restored wetlands through equipment hygiene, water management and approved biosecurity controls.
  • Monitor seasonal inundation, water depth, pH, temperature, colour, groundwater seepage, vegetation recovery and fish presence during suitable wet-period conditions.
  • Use the approved success criteria, but include persistence of wetland hydrology, suitable acidic water, intact moist peat and no construction-related decline in habitat condition.
  • Submit rehabilitation monitoring results and any confirmed species records to the project regulator and the relevant state wildlife database.

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