White Wrestling Halfbeak (Dermogenys cf. pusilla)

Choose a distinctive viviparous halfbeak

The White Wrestling Halfbeak (Dermogenys cf. pusilla) is a viviparous halfbeak in the family Zenarchopteridae. The genus occurs in fresh and brackish waters across South and Southeast Asia, from India to the Philippines and Greater Sundas. It suits an attentive keeper who can prepare a mature filtered aquarium, test the water regularly and monitor social behaviour. Males of the genus may be aggressive towards one another, so the keeper must respond if one fish is repeatedly displaced or prevented from feeding.

WoRMS recognises Dermogenys as an accepted genus within Zenarchopteridae. The cautious cf. pusilla label associates this pale trade animal with the familiar Wrestling Halfbeak while keeping its identity at genus level. Its scientific name should therefore remain Dermogenys cf. pusilla throughout the aquarium plan.

Wikipedia describes Dermogenys as a genus of viviparous halfbeaks. Both sexes have a lower jaw that extends well beyond the upper jaw, which gives the group its halfbeak name. The same genus account notes that males tend to be more brightly coloured and are well known for aggression towards one another. Use behaviour in the aquarium, rather than assumptions about sex or rank, to decide whether the social arrangement is working.

We rate this fish intermediate as a store suitability assessment. The rating reflects the need for mature filtration, regular testing, careful stocking and close observation of interactions. A prepared keeper can make clear decisions from daily behaviour and water tests; a newly filled aquarium or an unplanned mixed community leaves too little room to respond well.

Understand the purchase unit and dispatch sizes

One purchase supplies one White Wrestling Halfbeak. The live size selector uses the labels 3–4 cm and 4–5 cm; use the label to choose the dispatch size and set the quantity to the number of individual fish required. One fish is supplied for each purchase unit, not a pair, trio or pack.

The size you select is the size supplied, not the adult size. A dispatch measurement describes the approximate size of the animal prepared for the order. It does not identify a life stage, predict sex or set a limit on future growth. Plan the aquarium around the needs of a fully grown fish and leave enough capacity to revise the social arrangement as the animals develop.

The exact species has not been identified, so the care advice here follows the genus Dermogenys and its care group.

Sex is guaranteed only when the selected option explicitly states male or female. This White Wrestling Halfbeak listing has no sex-guaranteed option.

The word White is the established trade label for this pale form. It should not be read as a biological diagnosis or as a promise of one exact shade. Lighting, background and normal individual variation can alter the visible tone of a live fish.

The gallery images are representative of this type of animal rather than photographs of the exact animal supplied, so colours can look slightly different from the live animal.

Check whether the aquarium suits this fish

Start with a mature, filtered freshwater aquarium in which ammonia and nitrite both test at 0 mg/l. Check pH regularly, confirm that the aquarium remains stable and assess stocking from the animals’ eventual needs rather than from their dispatch measurements. OATA’s freshwater guidance is broad group guidance rather than a species-specific optimum: it recommends choosing an aquarium that can accommodate the fish when fully grown and notes that larger volumes are generally more stable.

Place the aquarium out of direct sunlight and away from heat, draughts, loud noise, vibration and sudden movement. Set it on a flat, level stand that can support the filled aquarium indefinitely. These choices reduce avoidable environmental fluctuations and make routine observation easier.

Use the first tropical aquarium guide to prepare the system before livestock arrives. Confirm that the equipment works, the filter processes waste and the water tests remain suitable after feeding or other normal demands on the aquarium.

Arrange the aquarium for observation and retreat

Choose the largest practical aquarium that can accommodate every intended inhabitant when fully grown. Larger aquariums contain more water and are generally less susceptible to rapid variations in temperature and pH than small aquariums. Allow for the space occupied by plants and decoration when judging the usable volume.

Build the layout around clear decisions

• Place the aquarium on a level support designed to hold its full weight indefinitely.
• Keep it away from direct sunlight, heaters, draughts, loud noise and vibration.
• Use plants and ornaments to provide retreat areas for less boisterous or reclusive fish.
• Leave clear areas where every animal can be counted and observed during feeding.
• Keep equipment accessible so flow, temperature and blockages can be checked promptly.

Plants and ornaments provide enrichment, but they also occupy swimming space. Add them with the needs of the complete community in mind. Live plants may help remove nitrate, while sheltered areas let a fish move away from activity elsewhere in the aquarium. Avoid packing the aquarium so densely that fish cannot be observed or waste cannot be removed.

Reassess the layout after introducing livestock. If one fish remains hidden, misses meals or repeatedly encounters another animal, first check water quality and then examine whether the layout provides useful retreat space. Move decorations only when the change has a clear purpose, because repeated rearrangement adds disturbance without addressing an unidentified cause.

Keep routine access straightforward. Filters, heaters and test points should remain reachable without dismantling the whole aquascape. A design that supports quick checks makes it easier to act when temperature, flow or fish behaviour changes.

Keep water stable and test it regularly

Keep ammonia and nitrite at 0 mg/l, check nitrate and pH, and monitor temperature regularly. Use test kits rather than judging water quality from appearance. Clear water can still contain toxic ammonia or nitrite, while an established testing routine shows whether feeding, stocking and maintenance are placing too much demand on the filter.

OATA advises checking water quality at least once a week and testing more frequently when setting up an aquarium or adding fish. Its freshwater sheet sets ammonia and nitrite at zero and recommends partial water changes of up to 25% every week as broad aquarium guidance. Apply the routine according to test results, aquarium size, stocking and feeding.

Use the water chemistry guide to understand what each test measures, then enter actual readings in the water matcher before comparing a potential community. Testing both the aquarium and replacement water helps prevent an abrupt change during maintenance.

Treat new tap water to make it safe for fish and match its temperature before adding it. Make changes deliberately rather than altering several variables at the same time. A written test record helps distinguish a gradual trend from a single unusual reading.

Mature the biological filter before adding fish

A mature biological filter is essential. The RSPCA explains that filter bacteria convert toxic ammonia into nitrite and then into safer nitrate. Filling an aquarium and switching on equipment begins preparation, but the system must also develop enough beneficial bacteria to process the waste produced by its inhabitants.

Dechlorinate the water before relying on the filter. OATA advises allowing a newly prepared aquarium 24–48 hours to settle so that equipment can be checked and the intended temperature reached, but that settling period is not the same as biological filter maturation. Continue testing ammonia and nitrite while the bacterial population develops.

Protect the filter’s biological function

• Stock the aquarium gradually so the bacterial population can adjust as waste and feeding increase.
• Check the filter for blockages and reduced flow during routine observation.
• Keep ammonia and nitrite at zero through testing, sensible feeding and maintenance.
• Avoid replacing all established biological media at the same time.
• Treat replacement tap water before it reaches fish or mature filter bacteria.

Stocking too many fish too quickly can cause new tank syndrome because the bacterial population cannot process the extra ammonia and nitrite. The aquarium’s capacity cannot be calculated from volume alone: body size, species needs, water requirements and compatibility all affect how many animals it can support.

If breathing, swimming or feeding changes, test the water before assuming disease. Check whether the filter has stopped, become blocked or been disturbed during maintenance. Restoring safe environmental conditions is the first practical response when ammonia, nitrite, temperature or circulation has moved away from the established routine.

Feed a measured diet without overloading the filter

Offer an appropriate fish food in portions that can be consumed without leaving uneaten material to decay. Diet and feeding needs vary between species, and fish may feed at the surface, throughout the water column or near the bottom. Watch where each animal takes food and distribute the meal so that every fish can eat.

Uneaten food contributes to ammonia, increasing the load on the biological filter. Begin with a modest portion, observe consumption and remove leftovers. More food is not the answer when one fish fails to eat; first check whether another animal controls the feeding area, whether water quality has changed or whether the fish’s behaviour differs from its normal pattern.

Use feeding as a daily health check

Keep variety appropriate to the fish being maintained, but introduce changes in a controlled way so acceptance and waste can be judged. Avoid adding several unfamiliar foods at once. A simple feeding record is useful when appetite, behaviour or body condition changes.

Observe the quietest fish rather than using the boldest individual as proof that the whole group has eaten. Feeding access is part of compatibility: two animals can share water conditions yet still be a poor match if one consistently prevents the other from taking food.

Follow the arrival procedure in the correct order

Prepare the aquarium before the parcel is due. Confirm that ammonia and nitrite are at 0 mg/l, the filter is working and the established water conditions are stable. Someone must be present to receive the parcel because live fish cannot be left unattended.

Read the delivery and Live Arrival Guarantee policy before the delivery day. Keep your order details ready and make sure the receiving person can film the opening continuously.

Use these arrival steps

1. Receive the parcel in person.
2. Start filming while the parcel is still sealed and the outer box is visible.
3. Open the parcel in one continuous take while keeping the animal inside the sealed bag visible.
4. Float the bag for 20–30 minutes before releasing the fish.
5. Never pour the bag water into the aquarium.

The continuous video is required for every delivery from the sealed parcel onward. It records the sealed parcel being opened and the fish while it is still inside the bag before anything is disturbed. If a Live Arrival Guarantee claim is needed, contact us the same day with the order number and video.

After release, observe posture, breathing and swimming without making several immediate changes to the aquarium. Test the water if behaviour differs sharply from normal. Keep the filter operating and avoid adding further livestock until the aquarium remains stable under its new waste load.

During the first week, confirm that the fish feeds, maintains normal condition and is not persistently displaced by another animal. Record any water-test movement after introduction. Gradual stocking gives the biological filter time to develop the additional bacteria needed as waste and feeding increase.

Use a consistent maintenance and observation routine

Observe the aquarium every day. Count the fish, check swimming and breathing, watch part of a feed and note changes in colour, temperament, body condition or appetite. Familiarity with normal behaviour makes a meaningful change easier to recognise.

Test ammonia, nitrite, nitrate and pH at least weekly, and check temperature regularly. Test more often after adding fish, changing feeding, interrupting the filter or seeing unusual behaviour. Keep ammonia and nitrite at zero and use results to decide whether waste control, stocking or filter performance needs attention.

Pair each warning sign with an action

Carry out partial water changes of up to 25% every week as OATA’s broad freshwater routine, adjusting frequency and size according to the species kept, aquarium size, stocking and test results. Match and treat replacement water before adding it. Remove accessible waste and check the filter without dismantling all established media at once.

Inspect filter flow and clear blockages before circulation falls significantly. Retain mature biological media because it houses bacteria that process ammonia and nitrite. If livestock health remains a concern after water and equipment checks, contact us for further guidance.

Plan social space without assuming a fixed group size

Plan the number of fish around the aquarium’s mature capacity, water stability and observed behaviour rather than around a fixed fish-per-litre formula. OATA notes that body size, species requirements, water parameters and compatibility vary too widely for one universal stocking number.

The genus account says males may be aggressive towards one another. Because sex is not guaranteed for this offer, do not build the plan around a presumed ratio. Begin with enough spare capacity to respond if social pressure develops, and make decisions from repeated behaviour rather than one brief encounter.

Distinguish manageable interaction from a failing plan

Increase aquarium stocking slowly. Each addition raises waste production and feeding, so the bacterial population in the filter must adjust. A larger aquarium may be more stable, but it still needs adequate filtration and maintenance.

Reassess the community as fish grow. The 3–4 cm and 4–5 cm labels describe dispatch sizes only. Plants and ornaments reduce usable space, while boisterous animals may require more retreat room than a calm group. The correct number is the one the mature aquarium can support while every inhabitant feeds, behaves normally and remains in stable water.

Screen every community candidate before mixing fish

Screen companions for matching water type, temperature needs, flow requirements, adult space and behaviour before adding them. OATA notes that some fish need shoals while others are territorial or aggressive, and that species may prefer different water and flow conditions. A shared retail category does not make two animals compatible.

Use the livebearers collection to identify animals for further comparison, not as a universal tank-mate list. Read the individual care requirements and judge the complete aquarium, including its mature stocking, feeding pattern and filter capacity.

Give particular attention to interactions between halfbeaks because males of Dermogenys may be aggressive towards one another. The offer does not guarantee sex, so watch the fish rather than assuming a planned ratio has been supplied. Persistent displacement, hiding or missed meals means the arrangement needs intervention.

Compatibility remains conditional. Aquarium dimensions, decoration, stocking order and individual behaviour can alter the result, while stable water alone cannot resolve social pressure. Introduce livestock gradually and observe ordinary feeding and resting behaviour before making another addition.

Monitor feeding, water and behaviour together

Judge the community through ordinary daily behaviour rather than the first minutes after introduction. A workable arrangement allows every animal to feed, maintain normal swimming and use retreat areas without persistent displacement. Keep water tests stable while observing these interactions because poor water can change behaviour across the entire aquarium.

Watch feeding access

Observe more than one meal. If the same fish repeatedly fails to eat, distribute the portion more effectively and determine whether another animal controls access. Do not keep increasing the total food, because leftovers add ammonia and place further demand on the filter.

Watch social pressure

Male Dermogenys may be aggressive towards one another. Record whether an interaction ends or continues, and whether one individual becomes hidden, loses condition or misses repeated feeds. Improve space and retreat opportunities where possible, then separate fish when persistent aggression continues.

Watch the shared environment

Check that every species remains suited to the same water type, temperature and flow. Test ammonia and nitrite after stocking changes and keep both at 0 mg/l. A community that looks calm may still be overloading the filter, so behaviour and water tests must be assessed together.

If a match fails, correct the cause rather than waiting for chronic stress to resolve itself. Water maintenance, feeding access and retreat space can be improved, but separation is appropriate when persistent aggression or incompatible requirements remain.

Answer the key questions before choosing this fish

How big does the White Wrestling Halfbeak get?

Plan the aquarium around a fully grown White Wrestling Halfbeak rather than the 3–4 cm or 4–5 cm dispatch size. The identity remains at genus level, so use an aquarium with spare mature capacity and reassess space as the fish grows.

What size aquarium does it need?

Choose the largest practical aquarium that can accommodate every inhabitant when fully grown. OATA notes that larger aquariums are generally more stable, while plants and ornaments reduce usable space; judge capacity from mature needs, filtration and behaviour rather than a fixed fish-per-litre rule.

How many White Wrestling Halfbeaks should I keep together?

Plan the number around mature aquarium capacity and observed behaviour rather than a fixed group figure. Male Dermogenys may be aggressive towards one another, so ensure every fish can feed and respond if one individual is persistently displaced.

Is the White Wrestling Halfbeak suitable for beginners?

We rate the White Wrestling Halfbeak intermediate because it needs mature filtration, regular testing, gradual stocking and careful observation of social behaviour. It suits a prepared keeper who can keep ammonia and nitrite at 0 mg/l and act when behaviour changes.

What does this fish eat?

Offer appropriate fish food in measured portions and watch where each animal feeds. Remove uneaten material because leftovers contribute to ammonia, and check water quality and social pressure if the fish suddenly loses interest in food.

What temperature and pH does it need?

Keep temperature and pH stable, measure both rather than guessing and test pH at least weekly as part of OATA’s broad freshwater guidance. Match replacement water to the established aquarium and confirm ammonia and nitrite remain at 0 mg/l.

Is the White Wrestling Halfbeak aggressive or likely to nip fins?

Male White Wrestling Halfbeaks may be aggressive towards one another. Monitor feeding, hiding and repeated displacement; the genus account does not establish a general fin-nipping rule, so judge interactions from the behaviour of the fish in the complete aquarium.

Which kinds of animals can live with it?

Consider animals whose water type, temperature, flow, adult space and behaviour match the established aquarium. OATA advises screening every species because some fish require shoals while others are territorial or aggressive; no tank-mate combination is automatic.

How does the White Wrestling Halfbeak arrive alive?

Someone must be present to receive the White Wrestling Halfbeak. Start filming every delivery while the parcel is sealed, open it in one continuous take with the fish still in the bag, float the bag for 20–30 minutes, and never pour the bag water into the aquarium.

Check the identity and care references

• WoRMS: Dermogenys — accepted genus and family placement.
• Wikipedia: Dermogenys — genus distribution, viviparity, jaw form and male social behaviour.
• OATA freshwater aquarium guidance — setup, maturation, testing, maintenance and stocking principles.
• RSPCA aquarium environment guidance — biological filtration and nitrogen-waste processing.
• Tropical Fish Co delivery policy — packing, receiving, acclimatisation and Live Arrival Guarantee procedure.