Empire Gudgeon (Hypseleotris compressa)

Conservation status

Victoria, Flora and Fauna Guarantee Act 1988: Critically endangered.

Breeding season

FishBase describes spawning in the warmer months but does not give calendar months. The pattern below is an indicative Australian planning guide for a warm-season breeder, not a site-specific breeding calendar. Confirm timing from local records and pre-clearance surveys.

Months are January to December. The supplied sources specify warmer months rather than calendar months, so local survey evidence should take precedence.

• Breeding: Spawning is reported in warmer months. Males establish territories, display breeding colours and guard attached eggs.
• Young: Eggs hatch after 10 to 14 hours. Juveniles use swiftly flowing water and may school in estuaries.
• Movement and dispersal: The species is potamodromous and uses connected river habitats. Juveniles may occur in fast-flowing water and brackish estuaries, but seasonal movement dates are not reported.
• Highest clearing risk: Risk is highest during the indicative warmer-month breeding period, particularly where works disturb submerged egg substrates, aquatic vegetation, branches, flowing water or estuarine connections.

Identification

The Empire Gudgeon is a small, fusiform eleotrid fish. Identification in the field is most reliable in clear, shallow water or from a close examination of captured fish, because colour varies with sex and breeding condition.

Adults have a normal fusiform body shape. The fin count is seven dorsal spines, eight to nine dorsal soft rays, one anal spine and 10 to 12 anal soft rays.

Adult size: Up to about 12 cm standard length

Typical reported length: About 5 cm standard length

• Females are brown to golden above and whitish below.
• Breeding males develop bright orange-red colouration on the head and belly.
• Breeding males have dorsal and anal fins that are bright red-orange at the base, with a dark sub-marginal stripe and lighter margins.

Identification: Sex and breeding colour

Sexual dimorphism is most apparent during the breeding season. Bright orange-red colouration and strongly marked fins indicate a breeding male, while females remain more subdued brown, golden and white.

• Do not rely on colour alone outside the breeding season.
• Record body form, fin counts, habitat and locality when confirming an identification.

Identification: Similar species and field signs

The supplied sources do not provide a comparison key to similar gudgeons or carp gudgeons. The species should therefore be confirmed using a regional freshwater fish key or an experienced fish ecologist where other eleotrids occur.

There are no reported tracks, scats, calls, eyeshine or terrestrial shelter signs. Relevant field evidence consists of live fish, specimens, environmental DNA or observations of breeding territories and egg patches on submerged surfaces.

• Look for small gudgeon-like fish in lower river reaches, still or flowing water, fast-flowing juvenile habitat and brackish estuaries.
• Treat eggs attached to rocks, logs, sand, aquatic plants or submerged branches as potential breeding evidence where adult Empire Gudgeons are present.

Distribution: Australian range

The species has a broad Australian distribution associated mainly with coastal drainages. The supplied sources describe a range from central Western Australia around northern Australia and down the east coast to southern New South Wales, with additional records from Papua New Guinea.

In Australia, the species occurs primarily in lower coastal drainages from central Western Australia, around the tropical north, and south along the east coast to southern New South Wales.

The sources do not provide a state-by-state occurrence table or named Australian bioregions. They also do not identify confirmed strongholds or discrete subpopulations.

Australian range described: Central Western Australia, tropical northern Australia and the east coast south to southern New South Wales

Other range: Southern central New Guinea

Named Australian bioregions: Not provided in the supplied sources

• Include lower coastal rivers, streams, estuaries and connected wetlands in the desktop search area.
• Consider both freshwater and brackish records because juveniles commonly occur in estuaries and the species tolerates seawater-level salinity.

Distribution: Population information

The supplied sources do not provide an Australian population estimate, density, trend or map of strongholds. FishBase reports the species globally as Least Concern, but that assessment does not replace project-level checks in areas with a state conservation listing or local habitat disturbance.

Global IUCN assessment reported by FishBase: Least Concern, assessed 14 February 2019

Population size and trend: Not reported in the supplied sources

• Use recent state databases, museum records, local fish surveys and agency advice to check whether the species is known from the project catchment.
• Do not infer absence from a lack of public records in a short section of river.

Habitat: Waterway habitat

Empire Gudgeons use lower coastal rivers and streams, including both flowing and still water. Habitat use changes with life stage, with juveniles more often recorded in fast-flowing water and estuaries.

Adults inhabit lower reaches of rivers, although they may occur further upstream. They use flowing or still water among aquatic vegetation, submerged branches and other in-water structure.

Juveniles often occur in swiftly flowing water and may school in brackish estuaries.

Typical adult setting: Lower river reaches, in flowing or still water

Juvenile setting: Swiftly flowing water and brackish estuaries

• Inspect pools, margins, slow runs, backwaters, vegetated edges and submerged woody structure.
• Include tidal or brackish reaches in habitat assessments where freshwater inflows and aquatic cover remain available.

Habitat: Physical limits and structure

The species is reported from tropical conditions between 10°C and 30°C and can tolerate temperatures up to 35°C. It can also tolerate pH from 5.0 to 9.1 and salinity equal to seawater.

The sources do not provide elevation limits, vegetation community names, channel dimensions or required water depths.

Reported temperature range: 10°C to 30°C

Upper temperature tolerance reported: Up to 35°C

Reported pH tolerance: 5.0 to 9.1

Elevation limit: Not reported

• Map aquatic vegetation, submerged branches, rocks, sand, weeds and connected estuarine habitat before works.
• Assess whether construction may remove cover or interrupt movement between river, stream and estuarine habitats.

Foraging habitat: Diet

The Empire Gudgeon feeds in shallow freshwater, river and estuarine habitats. It takes small aquatic animals and also grazes or collects plant and organic material.

The diet includes micro-crustaceans, cladocerans, mosquito larvae and other aquatic insect larvae. Algae and detritus are also consumed.

Animal prey: Micro-crustaceans, cladocerans, mosquito larvae and other aquatic insect larvae

Other food: Algae and detritus

Trophic level estimate: 2.9 plus or minus 0.35 standard error

• Treat vegetated margins, submerged woody structure, fine sediments and shallow edge habitat as potential feeding areas.
• Retain water quality and aquatic cover where works occur near lower river reaches or estuaries.

Foraging habitat: Foraging movement

The supplied sources do not report a foraging range, home range, daily movement distance or feeding density. FishBase classifies the species as demersal and potamodromous, indicating use of the lower water column and movement within connected freshwater systems.

• Survey connected pools, runs, margins and estuarine areas rather than relying only on the immediate work footprint.
• Avoid treating a single occupied patch as the full feeding area.

Breeding habitat: Breeding sites

Breeding occurs in warmer months. Males establish bottom territories and attract females, which attach eggs to hard or submerged surfaces where the male guards and fans them until hatching.

Eggs may be attached to rocks, sand, weeds, logs or other submerged plants and surfaces. The male guards the nest throughout the short incubation period.

Suitable breeding habitat therefore includes stable submerged surfaces within flowing or still water, together with nearby cover used by adults.

• Inspect submerged rocks, logs, branches, aquatic plants, weeds and sandy patches before works in occupied habitat.
• Avoid disturbing shallow edge habitat during the warmer-month breeding period where breeding adults or attached eggs are observed.

Breeding habitat: Breeding biology

The male establishes a territory on the bottom and displays bright breeding colours to attract a mate. A female may deposit up to 3,000 eggs, which hatch after 10 to 14 hours.

The supplied sources do not report age at maturity, lifespan, spawning frequency or a defined Australian breeding month range.

Breeding season: Warmer months

Eggs per spawning event: Up to 3,000

Egg attachment sites: Rocks, sand, weeds, logs or plants

Incubation: 10 to 14 hours

Hatching larva length: About 1 mm

Age at maturity: Not reported

Lifespan: Not reported

• Record the location and substrate of any egg patch and keep observations separate from adult presence records.
• Seek local fisheries or agency advice where works could affect a connected breeding reach.

Sheltering habitat: Cover and refuge

The species uses aquatic cover rather than terrestrial shelters. Adults occur among aquatic vegetation and submerged branches, while juveniles use fast-flowing water and estuarine habitat.

Submerged branches, aquatic vegetation, weeds, rocks and other in-water structure provide the documented physical cover associated with the species. The sources do not describe dens, burrows, hollows, roosts or specific refuge dimensions.

Documented refuge features: Aquatic vegetation, submerged branches, weeds, rocks and other submerged surfaces

Refuge dimensions: Not reported

• Retain submerged woody debris and aquatic vegetation where practicable within or beside the work area.
• Inspect isolated pools, vegetated margins, branch piles and shallow estuarine edges before dewatering or channel disturbance.

Sheltering habitat: Life-stage habitat

Adults are associated with lower river reaches and may use still or flowing water. Juveniles are often found in swiftly flowing water or brackish estuaries, where they may school.

• Assess upstream and downstream habitat, including estuarine connections, when planning barriers, crossings or dewatering.
• Treat connected aquatic habitat as potentially important even where fish are not detected at one sampling point.

Threats: Clearing and construction

The supplied sources describe habitat use and environmental tolerances but do not provide a species-specific Australian threat assessment. Project risks should therefore focus on direct disturbance to occupied water, loss of aquatic structure and interruption of connections between river and estuary habitats.

Removal of aquatic vegetation, submerged branches, rocks, weeds or other in-water structure may reduce cover, feeding areas and surfaces used for egg attachment.

Dewatering, excavation, bank works and sediment-producing construction may directly affect fish using lower river reaches, flowing water, still water or estuaries.

• Inspect and map aquatic habitat before clearing, excavation, crossings or dewatering.
• Stage works to retain connected flowing or still water and avoid unnecessary removal of submerged structure.
• Use fish rescue and relocation procedures where required by the relevant state authority or project approval.

Threats: Hydrology, fragmentation and roads

The species is potamodromous and uses connected freshwater habitats, while juveniles may use estuaries. Barriers, altered flows, culverts, weirs, dewatering and changes to freshwater and estuarine connectivity may therefore restrict access between life-stage habitats.

Road and utility crossings can disturb occupied channels and introduce barriers or altered flow conditions. The supplied sources do not quantify crossing impacts or identify a species-specific road mortality rate.

• Check whether crossings maintain fish passage and the connection between lower rivers, upstream habitat and estuaries.
• Assess changes to flow, salinity, pH, temperature and water depth because the species uses a broad but defined range of these conditions.
• Do not assume that salinity tolerance removes the need to protect freshwater inflows and estuarine connections.

Threats: Fire, predators and disease

The supplied sources do not identify species-specific impacts from fire, introduced predators, native predators or disease. Fire-related risks should be considered indirectly where catchment runoff, ash, sediment or altered streamside vegetation could affect aquatic habitat.

• Check for post-fire sediment, ash and water-quality effects before works in affected catchments.
• Follow aquatic hygiene and biosecurity procedures between waterways to reduce the risk of transferring fish pathogens or invasive organisms.

Survey methodology: 1. Aquatic habitat inspection

Survey the Empire Gudgeon in lower coastal rivers, streams, estuaries and connected wet areas. Focus on still or flowing water with aquatic vegetation, submerged branches and suitable juvenile habitat in fast-flowing reaches and brackish estuaries.

Map all waterbodies, drainage lines, pools, riffles, estuarine reaches and areas of aquatic vegetation within and downstream of the works area.

Inspect lower river reaches and connected upstream habitat because adults may occur in both lower reaches and further upstream.

Record water flow, salinity or conductivity, water temperature, pH, aquatic vegetation, submerged branches, bank cover and connections to estuarine habitat.

Give particular attention to habitat with temperatures up to 35°C, salinity approaching seawater and pH from 5.0 to 9.1, because the species tolerates these conditions.

• Undertake the inspection before clearing and repeat it after changes to water levels, flow paths or aquatic vegetation.
• Use the habitat inspection to select fish sampling sites and to identify areas that should be retained or fenced from machinery.

Survey methodology: 2. Active fish sampling

Use methods accepted by the relevant state or territory authority for small freshwater fish, such as seine netting, dip netting, bait traps or electrofishing where authorised and safe.

Sample representative still-water and flowing-water habitats, including vegetated margins, submerged branches, pools, faster-flowing reaches and connected estuarine habitat.

Use repeatable sites and record the sampled area, transect or net length, water depth, flow condition, method, start and finish times, weather and water quality.

The supplied documents do not provide species-specific sampling effort, so set the number and length of sites, passes and repeats using the applicable state fish survey guideline and the project's approved survey design.

• Obtain all required animal ethics, scientific collecting, fisheries and electrical fishing approvals before sampling.
• Release captured fish promptly at the point of capture unless the approval, animal welfare procedure or a qualified aquatic ecologist directs otherwise.
• Identify specimens using an experienced fish ecologist, because small gudgeons can be confused with other eleotrid fishes.

Survey methodology: 3. Breeding and recruitment checks

Include surveys in the warmer months when breeding activity is most likely to be observed.

Inspect rocks, sand, aquatic plants, logs and other submerged surfaces for attached eggs, and look for territorial males around potential nest sites.

Sample juvenile habitat in swiftly flowing water and brackish estuaries, where juveniles are often found and may school.

Record adult, juvenile, larval and egg observations separately, with the exact waterbody location and habitat type.

• Do not disturb suspected nests or remove attached eggs unless this is specifically authorised and necessary for an approved survey.
• Treat a confirmed nest, egg mass or concentration of juveniles as a stop-work or exclusion trigger until the aquatic ecologist and project environmental officer set controls.

Survey methodology: Minimum effort and reporting

• Use the relevant state or territory threatened fish survey guideline where one applies, because the supplied documents do not state a minimum number of sites, trap nights, transect length or survey hours for this species.
• Survey both retained and potentially affected aquatic habitat, including connected upstream and downstream reaches where works could alter flow, water quality or fish movement.
• Record negative results, not just captures, and document the method, effort, conditions, habitat, identification basis and any handling or release.
• Submit confirmed records and significant habitat observations to the relevant state wildlife or biodiversity database, and to the project approval authority where required.
• For Victorian works, check the current requirements for the state's Critically Endangered listing before fieldwork begins.

Before habitat disturbance: Avoid and minimise

Avoid disturbance to occupied aquatic habitat wherever practicable. The species uses lower river reaches, flowing and still water, aquatic vegetation, submerged branches and estuarine areas, so controls must cover the waterway and its connected margins.

• Retain flowing and still-water habitat, aquatic vegetation, submerged branches, vegetated margins, pools and connections between rivers and estuaries.
• Keep machinery, spoil, fuel, concrete washout and sediment out of the channel and its margins.
• Avoid changing water flow, isolating pools, removing aquatic vegetation or clearing submerged branches unless the approved design requires it.
• Maintain movement pathways between lower river reaches, upstream habitat and estuarine areas.

Before habitat disturbance: Approvals and timing

• Confirm the species' conservation status for every state or territory in the project footprint before works start.
• An EPBC referral is not indicated by the supplied information because the species is not listed under the EPBC Act, but check the current Commonwealth list and any project specific approval conditions.
• For Victorian works, obtain advice on the implications of the Critically Endangered state listing and secure any required wildlife, fisheries, scientific collecting and waterway permits.
• Plan in-channel disturbance outside the warmer-month breeding period where practicable, and avoid known nests, eggs and juvenile concentrations.

Before habitat disturbance: Site preparation

• Complete a pre-clearance aquatic habitat survey immediately before works, including water quality, flow, aquatic vegetation, submerged branches, nests, eggs and fish presence.
• Mark exclusion areas around retained water, vegetated margins, submerged habitat and any confirmed breeding site before machinery enters the work area.
• Use exclusion fencing, sediment controls and machinery access points that prevent entry into retained aquatic habitat where these controls suit the site.
• Prepare a fauna management plan that names the aquatic ecologist, spotter catcher or fish rescue team, authorised handlers, equipment, release locations, stop-work triggers and incident contacts.

During habitat disturbance: Daily controls

Treat work in or beside water as a live fauna risk. The fauna spotter catcher or aquatic ecologist should have authority to pause work when fish, eggs or suitable habitat may be affected.

• Inspect exclusion fencing, sediment controls, bypasses, pumps, screens and access points before work starts each day and after rainfall or flow changes.
• Keep machinery, refuelling, spoil, concrete, chemicals and dirty water away from the channel and retained habitat.
• Maintain fish passage and avoid stranding fish by preventing sudden isolation or dewatering of pools.
• Use clean equipment between waterways to reduce transfer of sediment, pathogens and aquatic weeds.
• Brief operators each day on the mapped exclusion areas, communication signal and stop-work procedure.

During habitat disturbance: Spotter and machinery coordination

• The fauna spotter catcher or aquatic ecologist must inspect the immediate work area before machinery moves, then remain in communication with the operator during aquatic disturbance.
• Stop machinery before the operator enters water, removes aquatic vegetation or disturbs submerged branches, rocks, sand or logs in a mapped exclusion area.
• Do not allow untrained workers to capture, handle, identify or relocate fish, eggs or larvae.
• Use only personnel authorised under the relevant permit and fauna management plan for fish rescue or relocation.

During habitat disturbance: If the species is found

• Stop work in the immediate area and keep machinery, people and sediment away from the fish, nest or egg site.
• Have an authorised aquatic fauna handler identify the animal and decide whether it can be released immediately at the capture point or needs an approved relocation.
• Relocate fish only to nearby retained habitat with suitable flow, cover and water quality, and only where the permit and fauna management plan allow it.
• Do not move eggs attached to rocks, sand, aquatic plants or logs unless an authorised aquatic ecologist directs the action under an approved procedure.
• Place injured fish in suitable clean, aerated water and contact the nominated aquatic wildlife carer, veterinarian or government wildlife authority without delay.

During habitat disturbance: Stop-work triggers and records

• Stop work if a fish, nest, egg mass or group of juveniles is found in the disturbance area, if fish become stranded, or if sediment, contaminated water or a flow change reaches retained habitat.
• Record the date, time, location, waterbody, habitat, species identification, life stage, number observed or handled, method, person responsible, action taken and release location.
• Record any mortality, injury, escape, failed relocation, water quality incident, permit breach or control failure and notify the project environmental officer promptly.
• Resume work only after the aquatic ecologist or delegated environmental officer confirms that controls are in place and the stop-work trigger has been resolved.

After habitat disturbance: Post-clearance checks

Check the work area and connected waterway after clearance and after any change to flow or water quality. Confirm that retained habitat and fish passage remain functional.

• Inspect the disturbed reach, retained margins, downstream pools and any temporary isolation points for stranded, injured or dead fish.
• Check that aquatic vegetation, submerged branches, flow paths and connections to upstream and estuarine habitat have not been removed or blocked beyond the approved footprint.
• Remove temporary barriers, pumps, screens, spoil and sediment controls only when the aquatic ecologist confirms that doing so will not strand fish or release polluted water.
• Repeat targeted fish and habitat checks where works caused dewatering, channel alteration, high turbidity or loss of aquatic cover.

After habitat disturbance: Monitoring and reporting

• Monitor retained habitat during the period specified in the fauna management plan, with extra checks after rainfall, high flows, dewatering or water quality incidents.
• Compare post-work observations with the pre-clearance records, including fish detections, aquatic vegetation, submerged cover, flow and water quality.
• Report all captures, mortalities, injuries, relocations, nests, eggs and confirmed sightings to the project environmental officer and the relevant authority where required.
• Submit verified occurrence records to the relevant state wildlife or biodiversity database.

After habitat disturbance: Ongoing controls and offsets

• Maintain exclusion fencing, sediment controls, water quality controls and fish passage measures until the site is stable and the environmental officer signs them off.
• Repair failed controls promptly and investigate any loss of aquatic vegetation, submerged cover or connection between habitats.
• Apply any offset, compensatory habitat or approval condition required by the relevant state or territory authority, particularly where Victorian listed habitat is affected.

Rehabilitation actions: Restore aquatic habitat

Rehabilitation should restore the shallow-water structure and connectivity used by Empire Gudgeons. Prioritise clean flowing or still water, aquatic vegetation, submerged cover and links to estuarine and upstream habitat.

• Re-establish stable channel margins and shallow areas with native aquatic vegetation suited to the local river or estuary.
• Replace suitable submerged branches and coarse woody cover removed by approved works, without creating barriers to fish movement or causing unsafe debris accumulation.
• Reinstate natural flow paths, pools and connections between retained reaches, upstream habitat and estuarine habitat.
• Use local native plant material and prevent weed establishment in and beside the waterway.

Rehabilitation actions: Water quality and threat control

• Prevent sediment, chemicals, concrete washout and contaminated runoff from entering rehabilitated habitat.
• Maintain water conditions within the species' documented tolerance where practicable, including pH from 5.0 to 9.1 and temperatures up to 35°C, without treating these tolerances as targets.
• Control introduced predators, pest animals and aquatic weeds where they threaten fish, eggs, aquatic vegetation or water quality.
• Plan fire and fuel reduction works to avoid loss of riparian shade, bank stability and aquatic cover.

Rehabilitation actions: Monitoring and success measures

• Inspect rehabilitation after construction, after major rainfall and during the monitoring period set by the approval or rehabilitation plan.
• Measure survival and cover of planted aquatic and riparian vegetation, stability of banks, continuity of flow, aquatic cover, sediment control and connection to adjacent habitat.
• Use repeatable fish surveys at the pre-clearance sites where practicable, recording the same method, area, conditions and effort so results can be compared.
• Treat successful rehabilitation as retention of connected flowing or still water, functioning aquatic vegetation and submerged cover, no persistent sediment or pollution issue, and no fish stranding caused by the works.
• Record Empire Gudgeon adults, juveniles, eggs and larvae separately and submit verified records to the relevant state wildlife or biodiversity database.

Sources

• Hypseleotris compressa (Krefft, 1864), fishbase.se: https://www.fishbase.se/summary/22755
• Empire Gudgeon, Hypseleotris compressa (Krefft, 1864), Australian Museum: https://australian.museum/learn/animals/fishes/empire-gudgeon-hypseleotris-compressa/