Cox's Gudgeon (Gobiomorphus coxii)

Conservation status

Victoria, Flora and Fauna Guarantee Act 1988: Endangered.

Breeding season

Timing varies with location and flow conditions. The pattern below combines the documented March to April breeding period with the reported downstream movement of young and upstream movement during spring and summer.

Months are Jan to Dec. The supplied sources do not provide a precise duration for the downstream juvenile phase or a site-specific migration window.

• Breeding and egg guarding: Spawning occurs in March and April. Eggs are laid on rocks, and the male guards and fans the nest until hatching after about 3 to 5 days.
• Young and downstream phase: Young are reported to be washed downstream during high flows in winter and spring, with juveniles generally occurring closer to the sea or at lower altitudes.
• Upstream migration: After the downstream phase, young fish migrate upstream. Upstream movement is reported during spring and summer, and fish can climb waterfalls and steep dams.
• Highest clearing risk: Risk is highest during March and April when eggs and guarded nests may be present, and from September to December when upstream movement is occurring. Winter and spring high flows may also carry young downstream, so in-stream disturbance should be controlled across this period.

Identification

Cox's Gudgeon is a small, moderately elongate gudgeon with a slightly flattened head. It is usually associated with flowing freshwater and may be encountered during aquatic fauna surveys, fish relocation or works near stream crossings.

Adults are brown, olive or purplish above, yellow to bluish on the sides and pale below.

Dark blotches occur on the upper sides, with a dark lateral stripe that may be continuous or broken into blotches.

Two brown bands extend backwards from the eye, and both dorsal fins have dark stripes.

Body form: Moderately elongate, with a slightly flattened head.

Maximum length: 19 cm total length.

Common length: About 15 cm total length.

Identification: Distinguishing features

The combination of a flattened head, dark lateral stripe or blotches, two bands behind the eye and striped dorsal fins supports identification.

The supplied sources do not provide a diagnostic comparison with other Australian gudgeons or information on sex-specific appearance. Confirm uncertain records with an experienced freshwater fish ecologist or an approved identification reference.

Identification: Field signs and handling

A live fish may be observed climbing a wet vertical wall, waterfall or dam face by pressing the inner surfaces of its pectoral fins against the wall.

This climbing behaviour is a useful field clue, but it is not sufficient on its own for identification.

There are no supplied records of diagnostic tracks, scats, calls, nests, sloughs or eyeshine. During works, record the capture location, stream flow type, altitude where known, photographs and release or relocation details.

Distribution: National range

Cox's Gudgeon is endemic to Australia and occurs along the south-eastern coast. Records extend from southern Queensland to southern Victoria, including coastal freshwaters and inland streams.

The documented range extends from southern Queensland through New South Wales to Victoria, reaching southern Victoria.

It occurs in coastal freshwaters and inland to about 700 m altitude. The supplied sources do not define the range by named IBRA bioregion.

States documented by the supplied range: Queensland, New South Wales and Victoria.

Recorded elevation: Up to about 700 m.

Distribution type: Endemic to Australia, restricted to the south-eastern coast.

Distribution: Strongholds and population status

Populations appear more abundant in southern rivers and flowing areas, including rapids. Adults are generally absent from lower reaches, while juveniles are more often found at lower altitudes.

The supplied documents do not provide a national population estimate, density, mapped stronghold list or confirmed population trend.

The supplied project information identifies the species as Endangered in Victoria and records it under the Victorian Flora and Fauna Guarantee framework. It is not listed under the EPBC Act according to the project information.

Habitat: Stream habitat

Cox's Gudgeon uses flowing freshwater from coastal streams to elevated inland waterways. Habitat requirements differ by life stage, with adults associated with upstream flowing areas and juveniles occurring closer to the sea or at lower elevations.

Adults occur in rapidly flowing water, including rivers, streams and rapids.

Southern river populations appear more abundant in flowing areas. The species can occur inland to about 700 m altitude.

The supplied sources do not identify particular vegetation communities, riparian plant species or a required canopy cover.

Water type: Freshwater, demersal habitat.

Flow character: Rapidly flowing water and rapids.

Altitude: Coastal streams to about 700 m inland.

Habitat: Structural features

Rocky surfaces are used for egg laying, and flowing water is associated with adult habitat.

Wet vertical surfaces, waterfalls and steep dams may provide movement routes because fish can climb them.

For site assessment, retain natural stream flow, rocky substrate, connected upstream and downstream reaches and wet passage surfaces where practicable.

Foraging habitat: Diet and feeding areas

Cox's Gudgeon feeds in freshwater, particularly in flowing areas used by adults. The supplied sources identify aquatic insects and mosquitofish as food items but do not describe a measured foraging range or feeding rate.

Adults feed on aquatic insects and mosquitofish.

The species is demersal and is associated with flowing water, including rapids, so feeding habitat is likely to occur on or near the stream bed in these areas.

No specific food plants, foraging distance, home range or feeding density is provided in the supplied documents.

Recorded food: Aquatic insects and mosquitofish.

Feeding setting: Flowing freshwater, including rapids.

Foraging range: Not reported in the supplied documents.

Breeding habitat: Breeding biology

Breeding occurs in freshwater during autumn. Eggs are attached to rocky surfaces, and the male guards and fans the nest until hatching.

Breeding season: March to April.

Eggs: Number of eggs is not provided in the supplied documents.

Egg site: Rocks and other rocky surfaces in freshwater.

Parental care: The male guards and fans the nest.

Incubation: About 3 to 5 days.

Age at maturity: Not provided in the supplied documents.

Lifespan: Not provided in the supplied documents.

Breeding habitat: Breeding sites

Breeding sites require rocky surfaces in flowing freshwater where eggs can be attached and guarded.

Activities that cover rocky substrate with sediment, reduce flow or isolate stream sections may affect egg attachment, nest maintenance or access to breeding areas.

The supplied sources do not define nest dimensions, preferred rock size or a required riparian vegetation structure.

Sheltering habitat: Known cover and refuge features

The supplied documents do not describe a separate refuge, burrow, hollow or roost used by Cox's Gudgeon. Available habitat information indicates that fish remain within freshwater stream environments, with adults concentrated in flowing upstream areas.

Adults are associated with flowing areas and rapids, while juveniles are generally found closer to the sea or at lower altitudes.

Rocky stream habitat provides the documented egg attachment and nest location, but the sources do not confirm that particular rocks, cavities or banks are used as shelters.

No refuge dimensions, burrow size, ground-cover requirement or seasonal shelter site is reported.

Documented shelter type: No separate shelter type is documented.

Associated habitat: Flowing freshwater, including rapids, with rocky surfaces.

Sheltering habitat: Site protection

Avoid isolating pools, removing rocky substrate or creating barriers between downstream juvenile habitat and upstream adult habitat.

Where fish are present during construction, use an aquatic fauna management plan and obtain the required Victorian approvals for handling or collection.

Threats: Construction and hydrology

Cox's Gudgeon is sensitive to changes that affect flowing-water habitat, rocky spawning surfaces and movement between lower and upper stream reaches. The supplied regional assessment identifies flow alteration, sedimentation, stream-bed and bank degradation, toxic chemicals and barriers to fish passage as relevant pressures.

Altered flow regimes can affect Cox's Gudgeon, particularly because the species uses flowing water and has a downstream young stage followed by upstream migration.

Dams, weirs, culverts and other structures may interrupt passage. The species can climb waterfalls and steep dams, but this does not mean every artificial barrier is passable.

Avoid isolating reaches, dewatering occupied habitat or diverting flows during works. Maintain fish passage and prevent sudden changes in downstream flow where practicable.

Threats: Sediment, banks and water quality

Increased sedimentation and turbidity are identified as important information gaps, but sediment deposition can affect rocky egg-laying surfaces and stream habitat.

Stream-bed and bank degradation is identified as an impact on Cox's Gudgeon and other priority aquatic species.

Toxic chemicals are likely to affect aquatic species depending on the substance and concentration. Prevent sediment, concrete washout, fuels, pesticides and other contaminants from entering waterways.

Threats: Clearing, fragmentation and fire

Clearing beside streams can increase bank instability, sediment input and changes to water temperature and flow conditions.

Fragmentation of connected stream reaches can restrict movement between juvenile and adult habitat and reduce access to breeding areas.

The supplied documents do not report a Cox's Gudgeon-specific fire response. Manage fire, access tracks and post-fire erosion to avoid sediment delivery and loss of stream-bank stability.

Threats: Predators and disease

The supplied documents do not identify a specific introduced predator or disease as a confirmed major threat to Cox's Gudgeon.

The regional assessment identifies introduced-species predation and competition as pressures on several native fish, and recommends preventing the spread of aquatic pests and pathogens during fish handling and relocation.

Survey methodology: 1. Inspect and map aquatic habitat

Cox's Gudgeon is a small freshwater fish of rapidly flowing waters, including rapids, and may occur upstream to about 700 m altitude. Adults are more likely in flowing habitat, while juveniles occur at lower altitudes and may move upstream during spring and summer.

Before selecting survey sites, map permanent and intermittent streams, rapids, steep channels, waterfalls, wet rock faces, pools and connected downstream habitat.

Prioritise flowing reaches and rapids, because adults are reported from these areas and are not usually found in lower reaches.

Record barriers such as dams, weirs, culverts and dewatered sections, because upstream movement is part of the species' life cycle and juveniles can climb waterfalls and steep dams.

Adult length: Up to 19 cm

Recorded altitude: Up to about 700 m

Spawning period: March and April

Likely upstream movement: Spring and summer

Survey methodology: 2. Undertake targeted fish surveys

Use a suitably qualified freshwater fish ecologist to select and apply an approved fish survey method for the waterway, such as methods authorised by the relevant state agency and project approval.

Sample representative flowing habitat, including rapids, shallow runs, pool margins and areas around rocks and logs.

Include lower-altitude connected habitat when juvenile movement is possible, because young fish may be washed downstream before later upstream migration.

Survey during suitable flow and water-quality conditions, and avoid sampling during unsafe high flows or when the method would cause unacceptable harm.

• Set the number of sites, pass numbers, survey area and repeat visits in the approved survey design rather than assuming a standard effort that is not specified in the supplied documents.
• Give particular attention to surveys during or following the March to April spawning period and during spring and summer upstream movement.
• Record effort, site length or area, water depth, flow, turbidity, temperature, habitat type, barriers and all fish captured or observed.
• Treat a negative result cautiously, because the supplied assessment identifies gaps in movement, larval habitat, turbidity tolerance and temperature tolerance data.

Survey methodology: 3. Check movement and breeding habitat

Search rock surfaces and stable logs in flowing water for potential spawning sites, noting that eggs are laid on rocks and guarded and fanned by the male.

Inspect wet vertical walls, waterfalls, steep dams and other structures for passable or impassable movement routes, because juveniles have been observed climbing wet walls and waterfalls.

Assess whether the project could interrupt the connection between downstream juvenile habitat and upstream adult habitat.

• Complete the movement assessment before finalising access tracks, crossings, temporary dams, pump locations or dewatering arrangements.
• Photograph and map spawning substrates, rapids, barriers and retained downstream and upstream habitat.
• Do not infer absence from a single visit, particularly where flow, turbidity or seasonal movement conditions are unsuitable.

Survey methodology: Minimum effort and reporting

• Use the survey effort and method required by the relevant state wildlife authority, project approval and qualified fish ecologist, because the supplied documents do not specify a standard number of nights, trap nights, transect lengths or survey hours for Cox's Gudgeon.
• Record the scientific name, observer, date, start and finish time, coordinates, waterway, method, effort, environmental conditions, photographs and identification basis for every record.
• Submit verified records and survey results to the relevant state wildlife database and provide the records to the project approval authority.
• Report all detections, mortalities, injuries, relocations, barriers and unexpected habitat impacts in the project environmental records.

Before habitat disturbance: Avoid and minimise

Plan works around connected flowing-water habitat and the species' movement period. Cox's Gudgeon is listed as Endangered in the supplied Victorian assessment and is identified there as an FFG-listed, migratory fish.

• Retain flowing stream sections, rapids, rocky substrates, stable logs, pool margins and riparian cover wherever practicable.
• Avoid placing crossings, culverts, temporary barriers, spoil, stockpiles or machinery access in or beside occupied or potential flowing-water habitat.
• Maintain a clear aquatic connection between retained upstream and downstream habitat, including during temporary works.
• Keep sediment, nutrients, pesticides and other toxic chemicals out of the waterway, because the assessment identifies stream-bed and bank degradation, altered flow regimes, sedimentation and toxic chemicals as risks to aquatic fauna.
• Treat wet rock faces, waterfalls and steep channel structures as potential movement habitat rather than removing or sealing them without assessment.

Before habitat disturbance: Approvals and work planning

• Check the current Victorian threatened-species listing, FFG requirements, collection or handling permissions and any local fish, waterway, dewatering or relocation approvals before work starts.
• Cox's Gudgeon is not listed under the EPBC Act in the supplied profile, but check the current EPBC protected-matters requirements and refer the project if another nationally protected matter or action trigger applies.
• Use a project fauna management plan that identifies aquatic habitat, survey results, exclusion zones, dewatering controls, authorised handlers, relocation arrangements, stop-work triggers and reporting responsibilities.
• Schedule in-channel disturbance outside periods of likely spawning and movement where practicable, with particular consideration of March to April spawning and spring and summer upstream movement.
• Stage works so that retained flowing habitat remains available while each work area is isolated, inspected and completed.

Before habitat disturbance: Prepare the site

• Complete the pre-clearance aquatic survey and confirm whether the work area contains flowing habitat, rapids, rocky spawning surfaces, logs, barriers or connected juvenile habitat.
• Mark no-go areas, stream buffers, spawning substrates, retained logs and access limits on plans and on the ground.
• Install exclusion fencing or equivalent controls where they can keep machinery, spoil and personnel out of retained stream habitat without blocking fish passage.
• Brief machinery operators and the fauna spotter catcher on the mapped habitat, approved access route, water-quality controls and immediate stop-work procedure.
• Prepare clean equipment, fish-handling equipment, aerated holding containers if authorised, recovery facilities and the contact details of the approving authority, aquatic ecologist and wildlife veterinarian.

During habitat disturbance: Daily controls and spotter coordination

Keep machinery and sediment away from flowing water and retain fish passage throughout the work. A fauna spotter catcher must not substitute for an approved aquatic fish survey or permit.

• Inspect exclusion fencing, stream buffers, crossings, pumps, screens, sediment controls and water-quality controls before work each day and after heavy rain or flow changes.
• Keep machinery on approved access routes and prevent refuelling, servicing, wash-down, concrete work and chemical storage where spills can enter the waterway.
• Use a fauna spotter catcher for terrestrial fauna and a qualified aquatic fish ecologist or authorised fish handler for fish capture, handling, salvage or relocation.
• Require the spotter catcher to have direct communication with the machine operator and authority to call an immediate stop when an animal, unexpected habitat or uncontrolled water-quality impact is found.
• Do not allow machinery to enter water containing fish until the approved isolation, salvage and dewatering procedure has been completed.

During habitat disturbance: Habitat and waterway handling

• Keep rocks, logs and bed material in place unless their removal is authorised and the aquatic ecologist has assessed the impact.
• If rocks or logs must be moved, inspect them first for fish and return them to suitable nearby habitat in the approved sequence.
• Isolate and dewater work areas gradually, prevent fish from being stranded, and use only the capture, holding and release methods authorised for the project and state.
• Maintain downstream flow and avoid sudden changes in discharge, because altered flow regimes can affect Cox's Gudgeon and other migratory fish.
• Do not use hollow-tree, nest-box or terrestrial burrow procedures for this species unless another fauna species is also present; the relevant features for Cox's Gudgeon are flowing water, rocks, logs, passage routes and connected habitat.

During habitat disturbance: If Cox's Gudgeon is found

• Stop the activity that could injure the fish or damage its habitat and keep people and machinery clear of the water until the authorised aquatic handler gives further direction.
• Do not collect, retain, transport or relocate the fish unless the person, method, equipment and release site are authorised under the project approval and relevant state requirements.
• Handle fish for the shortest practical time, keep them wet and shaded, and follow the approved fish-welfare and biosecurity procedure.
• Release a healthy fish into suitable nearby retained habitat with flow and connectivity, only where this is permitted and the aquatic ecologist confirms that the release site is appropriate.
• Take an injured or moribund fish to the nominated aquatic wildlife veterinarian or authorised wildlife carer, and notify the project environmental officer and relevant authority.
• If the fish is dead, preserve or photograph it as directed by the aquatic ecologist, record the location and likely cause, and report the mortality.

During habitat disturbance: Stop-work triggers and records

• Stop work for any Cox's Gudgeon detection in the active work area, fish stranding, fish mortality, uncontrolled sediment discharge, chemical spill, loss of downstream flow, damaged exclusion control or discovery of an unassessed barrier.
• Record the trigger, time, coordinates, waterway, activity, equipment, environmental conditions, photographs, fish numbers and condition, actions taken, handlers involved and release or veterinary outcome.
• Do not restart until the fauna management plan, aquatic ecologist and relevant approval conditions have been reviewed and the environmental officer authorises restart.

After habitat disturbance: Post-clearance checks

Confirm that works have not left fish stranded, blocked or exposed to poor water quality. Keep aquatic controls in place until the channel and banks are stable and the approval requirements are met.

• Inspect the full work area, upstream and downstream edges, pools, rapids, rock surfaces and log habitat for stranded, injured or dead fish.
• Check that temporary barriers, culverts, crossings, pumps and dewatered sections have not left an interruption to upstream or downstream movement.
• Remove temporary materials, spoil and sediment deposits that are not authorised to remain, without disturbing retained spawning or refuge habitat.
• Confirm that banks, bed material and riparian areas are stable and that no turbid, nutrient-rich or contaminated discharge is entering the stream.

After habitat disturbance: Monitoring and reporting

• Complete follow-up fish and habitat monitoring where required by the approval, fauna management plan or aquatic ecologist, with timing linked to the next suitable spawning or movement period.
• Compare post-work observations with the pre-work habitat map and survey records, including flow, turbidity, barriers, rocky substrate, logs and fish detections.
• Report all impacts, mortalities, relocations, approval breaches and corrective actions to the relevant authority and state wildlife database where required.
• Retain site photographs, survey data, chain-of-custody records, handling records and rehabilitation results in the project environmental file.

After habitat disturbance: Maintain controls and offsets

• Maintain sediment, erosion, chemical and access controls until the site is stable and the environmental officer confirms that they can be removed.
• Repair any damaged stream bank, crossing, barrier or fish-passage feature promptly and have the repair checked by the aquatic ecologist.
• Apply an approved offset or conservation measure if required by a state approval, significant residual impact assessment or other project condition.

Rehabilitation actions: Reinstate aquatic habitat

Rehabilitate the stream as connected, clean flowing habitat with stable rocky and woody structure. The supplied documents do not identify particular planting species or a species-specific rehabilitation target, so use locally appropriate native riparian species and an approved aquatic rehabilitation design.

• Restore natural channel shape, flow paths, riffles, runs and pools where these were altered by the project.
• Replace or retain suitable stable rocks and logs in flowing water where they formed part of the pre-work habitat, ensuring they cannot create an avoidable erosion or blockage risk.
• Re-establish stable banks and riparian cover to reduce erosion, shading loss and sediment entry near spawning and movement habitat.
• Do not leave temporary dams, perched culverts, abrupt drops or other structures that prevent movement through the retained waterway.
• Do not install fish passage structures without aquatic engineering and ecological assessment, because the species can negotiate steep natural and artificial features but passage performance is site-specific.

Rehabilitation actions: Riparian and water-quality management

• Plant locally native riparian species suited to the waterway and approved revegetation plan, rather than relying on a generic seed mix.
• Control weeds and prevent exposed soil, stock access, spoil and runoff from entering the stream.
• Prevent pesticide, fuel, concrete and other chemical contamination during establishment and maintenance.
• Manage introduced fish and other predators only through an approved program, because introduced species are identified as a potential source of predation or competition for native fish.

Rehabilitation actions: Monitoring and success measures

• Monitor bank stability, sediment deposition, water clarity, flow continuity, passage structures, rocky substrate, logs and riparian cover through establishment and after major flow events.
• Repeat targeted fish surveys during suitable spawning or spring and summer movement conditions where monitoring is required.
• Use successful re-establishment of connected flowing habitat, stable banks, retained or reinstated rock and log structure, no persistent project barrier, and Cox's Gudgeon detections where expected as project-specific success measures.
• Review rehabilitation prescriptions if monitoring identifies altered flow, excessive sediment, loss of passage, poor riparian establishment or continuing fish injury or mortality.

Sources

• Biodiversity Assessment, Australian Government DCCEEW: https://www.agriculture.gov.au/sites/default/files/sitecollectiondocuments/rfa/regions/vic-gippsland/enviroment/biodiversity/vic_gipps_bio.pdf
• Gobiomorphus coxii (Krefft, 1864), fishbase.se: https://fishbase.se/summary/52487
• Cox's Gudgeon, Gobiomorphus coxii (Krefft, 1864), Australian Museum: https://australian.museum/learn/animals/fishes/coxs-gudgeon-gobiomorphus-coxii-krefft-1864/