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Swamp Galaxias (Galaxias parvus)

The Swamp Galaxias, Galaxias parvus, is a small freshwater fish endemic to Tasmania. It occupies slow flowing swampy streams, shallow pools, marshes and temporary waters, so drainage works, culverts, earthworks and changes to water levels can affect habitat and fish movement on development sites.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Tasmania, Threatened Species Protection Act 1995: Vulnerable.

Breeding season

The timing below combines the documented breeding cycle with the species' use of temporary waters. The species should be surveyed seasonally because wet conditions can move fish into shallow ephemeral habitat.

Months are January to December. A value of 2 indicates peak activity or risk, 1 indicates occurrence, and 0 indicates that the activity is not typical or no fixed timing is documented.

  • Breeding and spawning: Spawning occurs in early spring, at approximately 8 degrees Celsius. The wild spawning site is not known.
  • Larvae and young: Larvae are present in November. Survey guidance states that juveniles start appearing in December to January.
  • Adult presence and detection: Adults occupy permanent and temporary freshwater habitat, but detection varies with water conditions. Seasonal sampling is recommended for ephemeral areas.
  • Highest clearing risk: Risk is highest from September to January because spawning, larvae and juveniles may be present, and wet conditions may place fish in shallow temporary waters. Site conditions should override calendar timing.

Identification

Swamp Galaxias is a small, stout galaxiid with a blunt head and rounded tail. It is secretive and is more likely to be detected in dense aquatic vegetation and shallow swamp habitat than in open water.

Adults are light brown on the back, with irregular small spots and flecks over the body. The underside is pale, the head is blunt and the tail is rounded.

The species reaches approximately 105 mm in length.

Body form: Small and stout, with a blunt head and rounded tail.

Colour: Light brown dorsally, with irregular small spots and flecks, and a pale underside.

Maximum length: Approximately 105 mm.

Weight: No weight information is provided in the supplied documents.

Identification: Distinguishing features

The supplied documents do not provide a full diagnostic comparison with other small Tasmanian galaxiids. Identification should therefore be confirmed by an appropriately qualified freshwater fish ecologist, particularly where climbing galaxias or other galaxiids occur.

Habitat and behaviour can support identification. Swamp Galaxias is associated with swampy, slow flowing water and is rarely seen in open water.

  • Record photographs, habitat, water depth, substrate, vegetation and associated fish whenever a suspected individual is captured.
  • Do not rely on colour alone, particularly for small or wet individuals.

Identification: Field signs

The relevant field sign is the presence of small galaxiid fish in shallow, soft bottomed water, dense aquatic vegetation, swampy runnels, drains or temporary pools.

The species is secretive and rarely seen in open water. Dip netting through thick aquatic vegetation is more likely to detect it than a visual search of open water.

  • Search shallow swamp margins, flooded vegetation, wheel ruts and temporary pools after wet weather.
  • Treat fish captured in occupied habitat as potentially significant until identification is confirmed.
  • There are no documented tracks, scats, calls, nests, sloughs or eyeshine signs for this species.

Distribution: Tasmanian range

Swamp Galaxias is endemic to Tasmania. The supplied documents identify catchment based populations rather than a complete statewide map or a national population estimate.

The species was historically known from the swamps, small streams and lake margins around the original Lake Pedder, and from the Wedge River and tributaries of the Huon River.

The current documented range includes swampy areas and suitable streams around the Lake Pedder impoundment, small streams draining to Lake Gordon near McPartlan Pass, and small streams in the Huon River catchment upstream of the Lake Pedder impoundment.

It is not recorded from the main body of the Lake Pedder impoundment or from Lake Gordon.

  • Lake Pedder and surrounding swamp and tributary systems.
  • Lake Gordon catchment near McPartlan Pass and the former Wedge catchment.
  • Upper Huon River catchment and associated creeks.

Distribution: Bioregional context

The records fall within south-western Tasmania, including the Lake Pedder and Lake Gordon areas and the upper Huon catchment. The supplied documents do not assign the species to a formal Interim Biogeographic Regionalisation for Australia bioregion.

The species is listed as an endemic fish recorded in reserves in the Tasmanian Temperate Rainforests and Highland Forests Conservation Management Zone. Within that zone, the source reports 93.78 percent of the species' total distribution and an estimated occurrence across 4.72 percent of the zone.

States: Tasmania only.

Known catchments: Lake Pedder, Lake Gordon near McPartlan Pass, the former Wedge catchment and upper Huon catchment.

Share of national distribution in the CMZ: 93.78 percent.

Estimated share of the CMZ occupied: 4.72 percent.

Distribution: Subpopulations and trend

The recovery plan identifies populations in the Serpentine, Huon and Wedge catchments as potentially genetically distinct. It also reports six sites considered relatively secure from introduced fish invasion.

The species declined after inundation of the original Lake Pedder and is affected by introduced fish and habitat barriers. The documents do not provide a total population estimate or a reliable count of mature individuals.

Relatively secure sites: Six sites were identified in the recovery plan.

Population estimate: No total population size is provided.

Trend: Past decline is documented, with continuing decline considered possible if threats are not controlled.

Habitat: Waterbodies and flow

Swamp Galaxias uses shallow, slow flowing and swamp associated freshwater habitats. Temporary waters can be important, especially during wet conditions.

The species inhabits slow flowing swampy streams with sandy or silty substrates. Habitats range from large, deep streams to small runnels.

It also occurs in swampy soft bottomed pools and shallow flooded margins of Lake Pedder. Larvae have been observed in backwaters of tributary streams.

  • Map permanent and temporary streams, drains, shallow swamps, flooded edges and wheel ruts within and downstream of the project area.
  • Include upstream and downstream habitat when assessing culverts, crossings, drainage changes or water level changes.

Habitat: Vegetation and structure

The supplied documents do not name particular plant communities or dominant plant species. They consistently associate the fish with swamp vegetation, dense aquatic vegetation, soft substrates and shallow water.

The species may move from permanent waters into shallow temporary waters during wet conditions, including drains, shallow swamps and wheel ruts.

  • Retain aquatic vegetation, shallow inundated margins and connected swampy depressions where practicable.
  • Avoid isolating shallow habitat from permanent water through spoil placement, drainage bunds or poorly designed crossings.

Habitat: Elevation and climate

The supplied documents do not state an elevation range or a defined temperature or rainfall limit. Habitat availability is strongly linked to wet conditions and the persistence of shallow freshwater areas.

Foraging habitat: Food

Swamp Galaxias feeds in shallow freshwater habitat, particularly around swamp vegetation, backwaters and soft bottomed margins.

The diet consists mainly of terrestrial insects, aquatic insects and aquatic crustaceans.

The documents do not identify particular prey species or quantify feeding rates.

Main food: Terrestrial insects, aquatic insects and aquatic crustaceans.

  • Protect aquatic vegetation and undisturbed swamp margins that support aquatic invertebrates.
  • Limit sediment inputs and water quality changes that may reduce invertebrate habitat or smother soft substrates.

Foraging habitat: Foraging sites and range

Likely feeding sites include shallow swampy streams, soft bottomed pools, backwaters, flooded lake edges and dense aquatic vegetation.

A foraging range or home range has not been reported. Because the species is non-diadromous and is associated with local freshwater habitat, project assessments should consider the full connected aquatic area rather than only the location of a single fish capture.

Foraging range: Not reported in the supplied documents.

Breeding habitat: Breeding biology

Breeding occurs in freshwater and is associated with spring conditions. The wild spawning site has not been identified, so all occupied swamp and stream habitat should be treated cautiously during spring and early summer works.

The species spawns in early spring when water temperatures are approximately 8 degrees Celsius. Larvae are present in November.

In captivity, eggs were deposited on gravel under shelter and hatched after 26 to 30 days at 10 to 15 degrees Celsius. The wild spawning site is not known.

Breeding season: Early spring, with larvae present in November.

Egg number: Approximately 70 to 500 large eggs.

Egg size: Approximately 1.6 to 2.6 mm.

Incubation: Approximately 26 to 30 days in captivity at 10 to 15 degrees Celsius.

Age at maturity: Smallest recorded mature males were one year old and females were two years old.

Lifespan: Survey guidance describes the species as appearing annual, with a life of about one year, but the recovery plan records females maturing at two years.

Gestation: Not applicable.

Breeding habitat: Breeding habitat features

Known habitat includes slow flowing swampy streams, shallow pools, backwaters and flooded margins with sandy or silty substrates. Captive spawning occurred on gravel under shelter.

Because the natural spawning location is unknown, do not assume that open water or a particular channel section is the only breeding habitat.

  • Retain shallow backwaters, swamp edges, gravel patches, aquatic vegetation and shelter within occupied catchments.
  • Prevent sudden drawdown, infilling, dewatering or isolation of shallow habitats during late winter, spring and early summer.
  • Use qualified aquatic fauna personnel and obtain required permits before capture, handling or relocation.

Sheltering habitat: Cover and refuge

The species shelters in shallow, structurally complex freshwater habitat rather than exposed open water.

Dense aquatic vegetation, swamp margins, soft bottomed pools, shallow runnels and backwaters provide the main documented cover types.

The species is secretive and was rarely seen in open water. Thick aquatic vegetation has been identified as an effective place to search for it.

  • Retain dense aquatic vegetation and avoid clearing or trampling shallow refuge areas.
  • Inspect temporary waterbodies, drains, wheel ruts and flooded vegetation after wet weather before they are filled, drained or compacted.
  • Do not assume that shallow or temporary habitat is unsuitable because it contains little open water.

Sheltering habitat: Structures not documented

The supplied documents do not report use of hollows, burrows, nests, dens, roosts or specific refuge dimensions. No fish shelter size or minimum water depth is provided.

Hollows or burrows: Not reported.

Refuge dimensions: Not reported.

Threats: Introduced fish

The main risks are introduced fish, loss of swamp and stream habitat, altered hydrology and barriers to movement. Small temporary habitats can be overlooked during project planning.

Brown Trout predates and competes with Swamp Galaxias. Climbing Galaxias has also increased in abundance and distribution and is implicated in the decline of the species.

Redfin Perch is a major potential threat. The recovery plan identifies the risk of redfin entering the Lake Pedder impoundment from Lake Gordon or through illegal introduction. Redfin can reach high densities and may enter slow flowing and swampy areas.

  • Prevent fish transfer between catchments through equipment hygiene, water movement controls and compliance with fisheries requirements.
  • Report suspected pest fish and do not release or move fish between waterbodies.

Threats: Habitat loss and hydrology

Inundation of the original Lake Pedder swamps and lower stream reaches caused direct habitat loss and was followed by decline in the species.

Changes to water levels, dewatering, drainage, infilling and loss of temporary pools can remove habitat or prevent access to shallow refuge areas.

  • Assess direct and downstream effects on permanent and ephemeral waters.
  • Maintain suitable water levels and avoid rapid drawdown where occupied habitat may be present.
  • Protect shallow swamps, backwaters, flooded edges and tributary connections.

Threats: Culverts and construction

Road culverts have created barriers to upstream movement in some occupied streams, with fish occurring downstream of the culvert only.

Clearing, access tracks, crossings, sediment runoff and spoil placement can remove or disconnect shallow habitat.

  • Inspect existing and proposed culverts for passage barriers, including drops, excessive velocity, perched outlets and loss of low flow connection.
  • Keep machinery, spoil and sediment controls out of shallow swamp margins and aquatic vegetation wherever practicable.
  • Include downstream habitat in impact assessments because works may affect fish beyond the project boundary.

Threats: Fire and disease

The supplied documents do not identify a species specific disease or quantify fire impacts. Fire related effects should be assessed through likely changes to swamp vegetation, erosion, sediment delivery, water temperature and flow persistence.

Avoid introducing aquatic pathogens or contaminated water between catchments during surveys and construction.

  • Use clean equipment and follow relevant freshwater fauna hygiene procedures between sites.
  • Assess post fire erosion and sediment risks before works in occupied catchments.

Survey methodology: 1. Map habitat and plan seasonal coverage

Survey the full area that may be affected, including temporary wetlands, drains, wheel ruts, shallow swamps, tributaries and downstream habitat. Swamp galaxias are secretive, use shallow vegetated water and may move into temporary habitat during wet conditions, so one survey at one location or in one season is not adequate.

Map permanent and temporary waterbodies, swampy streams, shallow pools, backwaters, dense aquatic vegetation, culverts and barriers before selecting survey sites.

Include areas that may be affected indirectly, including downstream areas and wetlands that may fill only after rain.

Plan repeat surveys across suitable wet conditions and seasons because swamp galaxias can move from permanent water into shallow temporary water, drains, shallow swamps and wheel ruts when conditions are wet.

Do not rely on a survey between about September and December to January, when the species may be absent after spawning and before juveniles appear.

Survey methodology: 2. Dip-net shallow habitat

Use fine or small dip nets in shallow water, especially through thick aquatic or emergent vegetation, soft-bottomed pools, swamp margins, drains and shallow runnels.

Sample slowly and systematically through cover because the species is secretive and is rarely seen in open water.

Give priority to dip-netting in shallow or ephemeral habitat, where it is likely to be more effective and less harmful than electrofishing.

Record the water depth, habitat type, vegetation, substrate, water level, weather and recent rainfall at every sampling location.

Survey methodology: 3. Electrofishing and other galaxiid methods

Use backpack electrofishing in suitable streams or lake margins only by trained operators, with settings and procedures that minimise harm and comply with the applicable code of practice.

For general Tasmanian galaxiid sampling, undertake at least 30 minutes of backpack electrofishing at each stream or lake-shore monitoring site.

Use a flat dip net to slide fish into a partly filled bucket, and use the lowest effective electrofishing setting for the water conductivity and habitat.

Consider fine, soft-mesh fyke nets overnight in suitable lakes or deeper permanent water, but do not substitute them for dip-net surveys of shallow ephemeral habitat.

Use night snorkelling or small hand nets only where safe and appropriate, and only by suitably trained personnel.

Survey methodology: 4. Minimum effort and reporting

  • Survey all suitable permanent and temporary habitat within the disturbance footprint and any area affected by downstream changes to water flow or quality.
  • Repeat surveys in wet conditions and at times when juveniles are expected, rather than relying on a single dry-weather visit.
  • Use at least 30 minutes of backpack electrofishing for each suitable stream or lake-shore site when electrofishing is selected.
  • Obtain the required animal ethics, collection and state permits before capture, handling, electrofishing, netting or temporary holding.
  • Have a qualified fish ecologist identify captures where field identification is uncertain, and release fish promptly at the capture location unless an approved conservation action applies.
  • Record positive and negative results, survey effort, methods, locations, dates, weather, water conditions, habitat condition, photographs and identification confidence.
  • Submit verified records and survey data to the relevant Tasmanian wildlife or biodiversity database and provide records to the project approval authority.

Before habitat disturbance: Avoid and minimise habitat loss

Treat all occupied catchments and suitable swamp habitat as potentially important until surveys show otherwise. The species has a limited Tasmanian distribution and depends on shallow swampy water that can be removed or fragmented by works.

  • Redesign the works to retain swampy streams, shallow pools, flooded margins, backwaters, dense aquatic vegetation and the catchments that maintain them.
  • Avoid filling, draining, diverting or isolating temporary wetlands, drains, wheel ruts and shallow runnels that connect to occupied or suitable habitat.
  • Maintain fish passage through streams and wetlands, and remove or redesign project barriers where they would restrict movement.
  • Prevent changes to water levels or flows that would dry shallow habitat or connect the site to waters containing introduced fish.
  • Use a clearly marked no-go area around retained water and wetland habitat, with the extent set by the project aquatic ecologist and approval conditions.

Before habitat disturbance: Approvals and work planning

  • Check whether the action may significantly affect this EPBC Act listed species and obtain environmental advice on whether an EPBC Act referral or approval is required.
  • Check Tasmanian threatened species, Inland Fisheries and reserve requirements before any capture, handling, fish movement, habitat disturbance or work on reserved land.
  • Prepare a fauna and aquatic habitat management plan that identifies survey results, exclusion areas, dewatering controls, capture authority, release arrangements, stop-work triggers and reporting responsibilities.
  • Schedule disturbance outside periods when fish are concentrated in shallow temporary habitat after rainfall, unless an approved ecologist determines that works can proceed safely.
  • Stage works so retained habitat remains connected and wet while each work area is cleared or constructed.

Before habitat disturbance: Pre-clearance preparation

  • Complete a pre-clearance aquatic survey immediately before works, including shallow temporary habitat that was dry during earlier inspections but has since filled.
  • Mark waterbodies, occupied sites, dense aquatic vegetation, culverts, barriers, access routes and machinery exclusion areas on site plans and in the field.
  • Install exclusion fencing or other physical controls where they can prevent machinery, stockpiled material, sediment or people entering retained wetland habitat.
  • Prepare clean nets, holding containers, aeration equipment, water-quality controls and an approved release plan before any dewatering or isolation begins.
  • Brief all operators on the species, its shallow-water habitat, the no-go areas, stop-work triggers and the fauna spotter catcher's authority.

During habitat disturbance: Daily controls and machinery interface

Keep works out of retained aquatic habitat and prevent sediment, altered flows and introduced fish from reaching it. The fauna spotter catcher must work as part of the machinery control process, not as a substitute for avoiding habitat.

  • Inspect exclusion fencing, wetland boundaries, flow controls, screens and sediment controls before work starts each day and after rain.
  • Use a fauna spotter catcher or aquatic ecologist to clear each work area and to direct machinery near water, wetland margins, culverts and dense aquatic vegetation.
  • Stop machinery immediately when the spotter identifies a fish, suitable occupied habitat, unexpected water, a failed exclusion control or a risk of fish movement into the work area.
  • Keep fuels, concrete washout, spoil, sediment, chemicals and dirty water away from retained water and prevent contaminated runoff entering drains or wetlands.
  • Do not transfer water, mud, plants, fish or equipment between catchments without approved decontamination and biosecurity procedures.

During habitat disturbance: Dewatering, habitat handling and fish capture

  • Avoid dewatering wherever practicable; where it is approved, isolate the area gradually and inspect shallow edges, vegetation, pools, drains and wheel ruts for stranded fish.
  • Use fine dip nets as the primary capture method in shallow vegetated habitat, and use electrofishing only by trained and authorised operators under the approved method statement.
  • Keep captured fish in a partly filled container with water from the capture site for the shortest practical period, and do not handle them without the required permit or authority.
  • Do not move swamp galaxias to another waterbody as an informal rescue action; release them only at the approved nearby retained habitat or other approved site.
  • Treat culverts, temporary crossings, barriers, logs, rocks and aquatic vegetation as habitat features, and do not remove or rearrange them without aquatic ecologist approval.
  • Maintain water quality, depth, flow and wetland connectivity around retained habitat throughout the work.

During habitat disturbance: Animal welfare, stop-work and records

  • Limit handling to trained and authorised personnel, and use an approved fish welfare and identification procedure.
  • Stop work and protect the location if a swamp galaxias is found, if fish are stranded, if a wetland unexpectedly fills, or if sediment, pollution or altered flow reaches retained habitat.
  • Keep injured fish in clean, site-appropriate water and arrange assessment by an appropriately authorised aquatic wildlife professional; do not release an injured fish without advice.
  • Record every capture, stranding, mortality, relocation, injury and release, including location, time, method, condition, photographs and the person responsible.
  • Report threatened species records, deaths, escapes, pollution events and approval breaches to the project environmental officer and the relevant state authority within the time required by the approval.

After habitat disturbance: Post-clearance checks

A site is not cleared of risk when machinery leaves. Check the disturbed area and retained catchment for stranded fish, blocked movement, sediment and changed water levels, then keep controls in place until the habitat is stable.

  • Inspect the full work area, temporary wetlands, drains, culverts, shallow pools and downstream habitat for stranded or injured fish after clearance and after the first substantial rainfall.
  • Check that retained aquatic vegetation, swamp margins, flow paths and fish passage have not been removed, blocked or isolated.
  • Remove temporary barriers, pumps, screens and sediment controls only after the aquatic ecologist confirms that doing so will not strand fish or release polluted water.
  • Repair failed erosion, sediment or flow controls immediately and record the response.

After habitat disturbance: Monitoring and reporting

  • Monitor retained and rehabilitated habitat during wet conditions and during the first seasons when temporary habitat is available.
  • Use repeat dip-net surveys in shallow vegetated habitat and the approved electrofishing effort where quantitative monitoring is required.
  • Compare occupancy, habitat condition, water levels, connectivity and introduced fish presence with the pre-work survey.
  • Report survey results, incidents, mortalities, corrective actions and database submissions to the approval authority and relevant state wildlife agency.
  • Keep exclusion fencing, water-quality controls and access restrictions in place until monitoring shows that the site is stable and the approval conditions are met.

After habitat disturbance: Offsets and residual impacts

  • Recalculate the residual loss or degradation of occupied or suitable habitat after avoidance and mitigation measures are applied.
  • Apply any offset, rehabilitation commitment or conservation payment required by the EPBC Act decision, Tasmanian approval or project condition.
  • Do not treat an offset as permission to remove avoidable swamp galaxias habitat or to proceed without the required approvals.

Rehabilitation actions: Rebuild suitable wetland habitat

Rehabilitation should recreate the shallow, slow-flowing and swampy conditions used by swamp galaxias. Prioritise wetland function and fish passage before cosmetic planting or landscaping.

  • Reinstate shallow, slow-flowing swampy channels, shallow pools, backwaters and flooded margins with sandy or silty soft substrates.
  • Re-establish dense local aquatic and emergent vegetation in shallow water and along wetland margins, using species selected for the local Tasmanian wetland community.
  • Restore natural or approved water levels and flows, and prevent drainage that would dry temporary habitat before fish can complete their life cycle.
  • Reconnect isolated pools, drains and tributaries where this can be done without creating access for introduced fish.
  • Retain or reinstate suitable woody and rocky cover only where it matches the local swamp habitat and does not obstruct fish passage.

Rehabilitation actions: Control threats and protect the catchment

  • Prevent brown trout, redfin perch and other introduced fish from entering rehabilitated habitat through stock movement controls, fish barriers or approved population management.
  • Maintain controls on the Lake Pedder to Gordon canal and other pathways where redfin movement could threaten swamp galaxias populations.
  • Inspect and modify road culverts or crossings that create barriers to upstream movement.
  • Control weeds and excessive sediment inputs so shallow pools, swamp margins and aquatic vegetation remain available.
  • Manage fire, access and earthworks in the catchment so wetland vegetation, soil structure and water quality are not degraded.

Rehabilitation actions: Monitoring and success measures

  • Inspect rehabilitated sites after rainfall and through the seasons to confirm that shallow water, swampy margins, aquatic vegetation, suitable substrate and connectivity persist.
  • Measure habitat condition, water depth, flow, water quality, vegetation establishment, culvert passage and introduced fish presence against the approved rehabilitation targets.
  • Use repeat dip-net surveys and other approved galaxiid methods to test whether swamp galaxias use the rehabilitated habitat.
  • Treat successful rehabilitation as retention or improvement of occupied habitat, area of occupancy, population security and connectivity, not simply vegetation cover.
  • Continue monitoring and corrective works until the project ecologist and approval authority accept that the site is self-maintaining or the required performance period has ended.

Sources