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Pygmy Rainbowfish (Melanotaenia pygmaea)

The Pygmy Rainbowfish is a small, schooling freshwater fish known from the Prince Regent River region of the western Kimberley. Its restricted known range makes careful checks of affected pools and tributaries important before works that could disturb aquatic habitat.

Conservation status

Western Australia, WA Threatened and Priority Fauna List: Priority 2.

Seasonal planning

Seasonal activity, breeding and movement information is not documented. Use the following as a planning window only, not as evidence that fish are more or less detectable or active in particular seasons.

Breeding season: Not recorded.

Survey timing: No species-specific seasonal survey window is recorded.

The month values indicate a year-round planning window, not documented species phenology.

  • Survey and work planning: Planning window only. No seasonal activity or detectability pattern is documented for this species; assess habitat and likely impacts at the site before works.

Identification: Appearance and size

Use a combination of colour, body form and location for identification. Detailed comparisons with similar fish are not available.

A small, relatively elongate and compressed rainbowfish. It is metallic sky-blue dorsolaterally, with a dark mid-lateral stripe and pale yellow to whitish fins.

Males are larger and more brightly coloured than females, with a reddish or orange head and a distinctive humped profile. Females lack the reddish head and have smaller, more rounded fins. The species reaches 5.5 cm standard length and is commonly 4 cm or less.

Identification: Similar species

Diagnostic differences from similar species are not documented. Confirm identification with a suitably experienced freshwater fish ecologist where other small fish are present.

Identification: Field signs

Schools of up to 50 or more individuals have been reported in freshwater pools and rivulets. Indirect field signs and species-specific survey detectability are not documented.

Distribution: Known range

The known range is restricted to the Prince Regent River area of the western Kimberley. Mapped occurrences are incomplete and should not be treated as a full map of occupancy.

The species is known from two small tributaries of the Prince Regent River in the western Kimberley region of Western Australia. The tributaries are not named.

Distribution: WA records and region

The DBCA priority list flags the Kimberley region. Atlas of Living Australia records show nine WA observations in four distinct 0.1 degree locations, spanning latitude -16.8 to -15.6 and longitude 125.3 to 125.6. These records do not include named localities.

WA status: Priority 2 on the DBCA Threatened and Priority Fauna List, dated 1 July 2025. This is a DBCA priority category, not a listing under the Biodiversity Conservation Act 2016.

Other listings: No national listing is recorded.

Habitat: Recorded habitat

The documented habitat is confined to freshwater features in the Prince Regent River region. Water chemistry, seasonal flow patterns and broader catchment requirements are not documented.

The species occurs in freshwater pools and rivulets on sandstone terraces, often at the base of small waterfalls and rapids. Schools of up to 50 or more individuals have been reported.

Habitat: Site context

When assessing a works area, check pools, rivulets, waterfall bases and connected tributary reaches within the potential disturbance footprint. Do not assume that an unrecorded or unsurveyed water feature is unoccupied.

Foraging habitat: Recorded diet

Food types are documented, but feeding locations, methods and daily feeding periods are not.

The Pygmy Rainbowfish feeds on small aquatic and terrestrial insects and microcrustaceans.

Foraging habitat: Precaution for works

Avoid sediment, contaminants and debris entering pools and rivulets. These are practical water-quality precautions; particular pollutants or food-resource threats have not been identified for this species.

Breeding habitat: Known breeding information

The species lays demersal eggs, but spawning sites, breeding season and egg-development period are not documented.

The species is oviparous and has demersal eggs. Sexual maturity is reported at 23 mm standard length. Clutch size and breeding months are not recorded.

Breeding habitat: Precaution

Treat occupied pools and rivulets as potentially important throughout the year because seasonal breeding timing is not recorded. Avoid draining, isolating or physically disturbing these waters where practicable.

Sheltering habitat: What is known

Specific sheltering behaviour and refuge use are not documented.

The species occurs in pools and rivulets on sandstone terraces, often at waterfall and rapid bases. Whether it shelters among rocks, vegetation or other structures is not known.

Sheltering habitat: Site precaution

Avoid unnecessary disturbance to the bed, banks and flow paths of occupied or potentially suitable water features. Do not infer a particular shelter type from the habitat description.

Threats: Recorded status

Specific threats to the Pygmy Rainbowfish have not been identified. Its restricted known distribution and limited occurrence information warrant a precautionary approach.

The species is listed as Priority 2 on the DBCA Threatened and Priority Fauna List, dated 1 July 2025.

Threats: Works-related risks to manage

Prevent avoidable physical disturbance to aquatic habitat, changes to flow, sediment input and pollution during works. These are precautionary controls for the described freshwater habitat, not threats specifically documented for this species.

Survey methodology: 1. Desktop assessment

Species-specific survey methods, survey seasons and detectability are not documented. Focus surveys on the known habitat and minimise disturbance.

Check mapped records and identify pools, rivulets, tributaries, sandstone terraces, waterfall bases and rapids within and near the proposed disturbance area. The recorded range is limited to the Prince Regent River region.

Survey methodology: 2. Habitat inspection

Have a suitably experienced freshwater ecologist inspect relevant water features before works. Record the extent and condition of the habitat and any fish observations, including the location and survey conditions.

Survey methodology: 3. Fish observations

Use a survey approach selected by the ecologist to suit the water feature and minimise harm or disturbance. Fish have been reported schooling, but they may not be present, visible or detectable in every suitable pool.

Vegetation associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific vegetation association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Ecosystem associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific ecosystem association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Soil and substrate associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific soil association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Water and wetland associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific water association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Fauna records and mapped habitat: Not yet analysed

Record locations can be overlaid with mapping, but record frequency alone does not measure habitat preference. No species is excluded from desktop assessments by this analysis.

No quality-controlled record-to-map analysis has been completed for this species. The existing generalised distribution dots and indicative range polygons have not been treated as precise occurrence coordinates.

A defensible run needs dated, independently attributable records, coordinate uncertainty, duplicate and captive-record checks, layer versions and regional scope. Preference and absence require additional survey-effort and detection evidence.

Habitat limitations and contrary evidence: No supported exclusion recorded

Not recorded is not the same as cannot occur. Low suitability, resident habitat, breeding habitat and occasional movement are different conclusions.

This library has not established a vegetation, ecosystem or soil-type exclusion for this species. This does not mean all habitat is suitable; the evidence needed to justify an exclusion has not been assembled.

Habitat limitations and contrary evidence: Before using a negative association

  • Confirm the taxon, geographic region, life stage and habitat function covered by the evidence.
  • Check survey methods, season, repeated effort and detectability before interpreting non-detection.
  • Investigate credible contradictory records and microhabitats absent from broad mapping.
  • Do not convert a missing map class, low record count or failed data request into species absence.

Before habitat disturbance: 1. Confirm the footprint

Plan works around the small freshwater features associated with the species and confirm the extent of potential impacts before clearing or ground disturbance begins.

Map the proposed works against pools, rivulets, tributaries and waterfall or rapid bases. Include areas that could be affected indirectly by runoff, access or changes to water flow.

Before habitat disturbance: 2. Survey and brief crews

Arrange a pre-disturbance habitat inspection and any necessary fish survey with a suitably experienced ecologist. Brief the clearing crew on aquatic exclusion areas, pollution controls and the stop-work process if fish or unexpected aquatic habitat is encountered.

Before habitat disturbance: 3. Set controls

Mark no-go areas and establish controls to keep sediment, fuels, chemicals and debris out of water features. Confirm the required approvals and response arrangements before any fish handling or relocation is considered.

During habitat disturbance: 1. Maintain exclusion areas

Keep disturbance away from aquatic habitat wherever possible and respond cautiously to any fish observed during works.

Keep machinery, stockpiles and unnecessary foot traffic out of marked water features and their protected work buffers. Do not block, drain or redirect pools and rivulets without an approved plan.

During habitat disturbance: 2. Control runoff and spills

Use the site controls to prevent sediment, fuel, chemicals and debris entering water. Stop and contain any spill promptly, and notify the site environmental lead.

During habitat disturbance: 3. Respond to observations

If fish are seen in an area at risk, pause the relevant activity and contact the site ecologist. Do not capture, handle or relocate fish unless the action has been assessed and authorised.

After habitat disturbance: 1. Inspect affected areas

After works, check that controls have protected nearby freshwater habitat and address any impact promptly.

Check water features and adjacent work areas for sediment entry, spills, debris, altered flow or physical damage. Record observations and report any suspected impact to the site environmental lead and ecologist.

After habitat disturbance: 2. Follow up

Where a fish observation or habitat impact has been recorded, seek ecologist advice on appropriate follow-up checks. A species-specific monitoring interval or protocol is not documented.

Rehabilitation actions: 1. Restore site conditions

Rehabilitation should avoid further harm to freshwater features and address the actual impacts of the works. A species-specific rehabilitation prescription is not documented.

Stabilise disturbed ground and manage runoff to reduce further sediment or contamination entering pools and rivulets. Retain natural flow paths and avoid unnecessary changes to water features.

Rehabilitation actions: 2. Check recovery

Have an ecologist review the affected habitat and confirm whether additional remedial action is needed. Do not introduce fish or alter aquatic habitat as a rehabilitation measure without appropriate assessment and approvals.

Sources