Swordtail Marry Gold (Xiphophorus helleri mary gold)

Meet the Marry Gold swordtail

The Swordtail Marry Gold (Xiphophorus helleri mary gold) is a poeciliid livebearer associated with a species native to North and Central America, from the Rio Nantla area of Veracruz, Mexico, to north-western Honduras. It reaches 14 cm, so it suits a keeper prepared to provide swimming length, stable water and companionship rather than treating its dispatch size as its final size. A mature, filtered aquarium with open swimming room and planted cover gives this active-bodied fish an appropriate long-term setting.

FishBase records the species in freshwater and brackish environments, including rapidly flowing streams and rivers, warm springs, weedy canals and ponds. Adults favour heavily vegetated places and feed on worms, crustaceans, insects and plant matter. These wild observations explain why aquarium planning should combine vegetation with open room and why the diet should contain both animal and plant ingredients.

FishBase now lists the species as Xiphophorus hellerii. Marry Gold is the trade name of this swordtail, and its care follows the species. Seriously Fish gives a smallest aquarium base of 120 × 30 cm, equivalent to about 108 litres. Plan the aquarium around the 14 cm adult rather than the size of a newly supplied fish.

Keep the aquarium at 22–27°C, pH 7.0–8.0 and 10–12 dGH. These values are the shared overlap of FishBase’s recorded environment, Seriously Fish aquarium guidance and OATA’s platy and swordtail guidance. OATA contributes group guidance, including the suggestion to keep at least three swordtails. OATA describes most platies and swordtails as easy to keep; this swordtail still needs the space, mature filtration, compatible water and weekly maintenance set out below.

Choose the dispatch size and plan ahead

One purchase supplies one Swordtail Marry Gold in the size chosen from the live size selector. The labels are 4–5 cm, 5–6 cm and XL. The size you select is the size supplied, not the adult size. XL has no centimetre measurement, so make the same 14 cm adult plan for every choice.

Sex is guaranteed only when the selected option explicitly states male or female. This Swordtail Marry Gold listing has no sex-guaranteed option. Group planning must therefore allow for the fish received and for the behaviour observed after introduction. OATA suggests keeping at least three swordtails, two females to each male, to reduce stress on females and other tank inhabitants, and FishBase records that males are aggressive towards each other.

The gallery images are representative, based on reference photographs of this species, so colours can look slightly different from the live animal. Two fish appearing in a gallery scene does not change the purchase unit: one purchase supplies one animal. Gallery scenes can help illustrate body shape, planting and swimming space, but base the aquarium decision on the stated adult size and husbandry values.

Browse the livebearers collection when comparing related fish, but assess every proposed combination against the Marry Gold’s adult size, water range and behaviour. Similar retail categories do not by themselves make two fish compatible.

Plan the aquarium around the adult size

Plan for a 14 cm adult and use an aquarium with a base of at least 120 × 30 cm or an equivalent footprint. Seriously Fish describes approximately 108 litres as the smallest volume to consider with those surface dimensions. The footprint matters because it provides usable horizontal swimming room; a differently shaped aquarium should still offer equivalent base space rather than reaching the volume through extra height alone.

FishBase also gives a minimum aquarium length of 80 cm, but the 120 × 30 cm species plan is the more spacious aquarium recommendation and should guide the finished setup. OATA gives 80 litres for swordtails generally. Those figures describe different planning measures, so do not substitute an 80 cm length or an 80 litre volume for the complete 120 × 30 cm footprint.

Separate supplied size from finished size

• 4–5 cm: this is a dispatch measurement, leaving substantial growth before the 14 cm adult plan.
• 5–6 cm: this also remains below the recorded adult figure and does not reduce the space requirement.
• XL: this grade has no centimetre value attached, so the aquarium must still be ready for a 14 cm swordtail.

FishBase records a maximum total length of 14 cm for Xiphophorus hellerii, so choose the aquarium, group and filter for a 14 cm adult.

Space must also account for the intended group and any companions. Seriously Fish reports that males in confined spaces form dominance hierarchies and may spend substantial time maintaining their positions. More fish therefore require more than a simple repetition of the individual body length: retain open swimming room, cover and enough total footprint for individuals to move apart.

Before choosing a size, measure the aquarium base rather than relying on its model name. A nominal volume alone cannot show whether the tank reaches 120 cm in length and 30 cm front to back. If the aquarium falls short, complete the larger setup before arranging the fish.

Set the water range before introduction

Keep the Swordtail Marry Gold at 22–27°C, pH 7.0–8.0 and 10–12 dGH. The temperature is the shared portion of FishBase’s 22–28°C environment, Seriously Fish’s 16–28°C aquarium range and OATA’s 22–27°C swordtail range. The pH range of 7.0–8.0 is shared by all three, while 10–12 dGH is where FishBase’s 9–19 dH, Seriously Fish’s 10–25 dGH and OATA’s 4–12 dH guidance meet.

Measure the aquarium before introducing the fish. Temperature alone is not enough: test pH, general hardness, ammonia, nitrite and nitrate so the decision reflects the water the animal will enter. Our water chemistry guide explains what the individual readings mean, while the water matcher lets you compare measured values with the stated range.

Use the numbers as practical limits

• At 22°C: the aquarium sits at the lower end of the routine temperature range; keep it stable rather than allowing it to fall below that value.
• At 27°C: it sits at the upper end; avoid allowing routine conditions to rise beyond it.
• At pH 7.0 or 8.0: the reading remains within the stated range, but regular testing is still required.
• At 9 dGH: the water is below the 10–12 dGH target, so bring the hardness into range before introducing the fish.
• At 13 dGH: the water is above the 10–12 dGH target, so bring the hardness into range before introducing the fish.

OATA sets ammonia and nitrite at zero mg per litre and says nitrate should not exceed 20 mg per litre above the normal tap-water level. These waste readings are separate from pH and hardness: acceptable mineral values do not compensate for measurable ammonia or nitrite.

Record readings consistently so a change can be recognised before it becomes severe. If a value moves outside the target, pause further stocking, check the aquarium and restore suitable conditions without making an unmeasured change. Stability comes from a mature filter, regular maintenance and additions made slowly.

Build a mature, filtered layout

Use a well-established biological filter in every Swordtail Marry Gold aquarium. The RSPCA explains that filtration is vital because fish release toxic ammonia; beneficial bacteria convert it to nitrite and then to the safer nitrate. The aquarium must be matured before livestock is added, rather than relying on the fish to establish the filter.

For an aquarium of about 108 litres, Seriously Fish suggests turnover of four to five times the aquarium volume per hour and a filter rated at roughly 430–540 litres per hour. Check the intended filter rating against that aquarium size. Filtration does not need to be particularly strong, although this swordtail seems to appreciate some water movement.

Balance cover with swimming room

Décor is not critical, but a heavily planted layout with a dark substrate shows this swordtail well, and floating plants with driftwood roots or branches diffuse incoming light.

• Cover: use live plants where practical; where live plants are not used, OATA recommends plastic plants and suitable ornaments such as plant pots or model caves for shelter.
• Open space: retain an unobstructed area for swordtail swimming, especially when planning a group.
• Water movement: provide filtration with some circulation without turning the full aquarium into a forceful current.
• Access: position décor so routine siphoning and filter checks remain practical.

Prepare and cycle the system before the arrival date. Our guide to preparing a first tropical aquarium provides a setup sequence, but the final decision still rests on measured water: ammonia and nitrite must be zero, and the temperature, pH and hardness must match this fish’s routine range.

Seriously Fish advises that an aquarium of about 108 litres needs roughly a 75–125 W heater when the room is around 20°C. Choose heating by the aquarium volume, room conditions and target of 22–27°C, then confirm the actual result with a thermometer instead of relying only on the wattage label.

Feed a balanced omnivore diet

Feed a varied omnivore diet once a day, offering only what the fish can finish within a few minutes. No single ingredient covers the whole diet: wild swordtails consume worms, crustaceans, insects and plant matter, while stomach analysis reported by Seriously Fish also includes aquatic and terrestrial invertebrates, organic detritus and algae.

Use a good-quality dried food as the regular base and vary it with small live or frozen foods. Seriously Fish names Daphnia, Artemia and chironomid larvae such as bloodworm. OATA recommends a quality flake or granule with a high algae content for platies and swordtails, alongside small daphnia, bloodworm or tubifex. Together, these choices match a generalised omnivore that consumes both animal and plant material.

Build each feed around three decisions

Watch the fish during the feeding period. Food remaining after the fish has stopped eating is not an extra reserve; OATA warns that uneaten food breaks down and releases toxic waste. Reduce the next portion when food is repeatedly left, then check ammonia and nitrite if waste has accumulated.

Match particle size to what the supplied fish can take readily. A 4–5 cm fish may need smaller pieces than a larger individual, but the ingredients and once-daily schedule remain the same. Break or select food so it can be eaten within the stated few-minute window rather than extending feeding time.

A practical rotation might use the balanced dried food on most feeds and substitute or supplement a small live or frozen item for variety. The exact rotation can change, but every feed must remain within the single daily allowance. Judge the portion by consumption, body condition and water cleanliness, not by how much food fits into a spoon or pinch.

Protect water quality each week

Carry out a 25% partial water change at least once every week. Use a siphon to remove solid waste from the substrate and treat replacement tap water with conditioner before adding it to the aquarium.

Test ammonia and nitrite at least once per week and keep both at zero mg per litre. Check nitrate against OATA’s limit of no more than 20 mg per litre above the normal tap-water level. Include temperature, pH and hardness in the routine so the fish is not exposed to a gradual movement outside 22–27°C, pH 7.0–8.0 or 10–12 dGH.

Service the filter without stripping its bacteria

Check the filter for blockages during maintenance. When cleaning is needed, do not rinse it under the tap. Lightly rinse the media in aquarium water removed during the partial water change, because chlorine or chloramine in tap water may kill the beneficial bacterial population established in the filter.

• Before the change: record the water readings and look for leftover food or unusual waste.
• During the change: remove 25% of the water and siphon debris from accessible substrate.
• Before refilling: condition replacement tap water to remove chlorine or chloramine.
• At the filter: restore flow by clearing blockages and rinsing media lightly only when needed.
• After refilling: confirm normal operation and recheck any value that caused concern.

Observe swimming, breathing, colour, appetite and body condition between services. OATA highlights hanging at the surface, sitting on the bottom, erratic swimming, unusual hiding or aggression, faster or slower gill movement, white spots, fluffy growths, fin or scale loss, weight change and reduced feeding as warning signs.

If you see a marked change, test the water first and contact us for guidance on the next step. Water readings, recent stocking, feeding and maintenance history give useful context for assessing the change.

Increase stocking slowly

Add fish only after the aquarium is mature, filtered and within the stated water range. OATA warns that aquarium populations must be increased slowly because the beneficial bacteria established in the filter need time to grow as fish numbers, feeding and waste increase. A mature aquarium can still be overloaded by a large, sudden addition.

Before the first introduction, confirm ammonia and nitrite at zero mg per litre, temperature at 22–27°C, pH at 7.0–8.0 and hardness at 10–12 dGH. Check that the base reaches at least 120 × 30 cm or an equivalent footprint and that the layout leaves both cover and open swimming room.

Use staged checkpoints

• Before adding the fish: test the water, check filter flow and confirm that the intended group and companions fit the finished aquarium.
• During the first observations: look for normal swimming, breathing and interest in food without adding more livestock immediately.
• As feeding begins: offer the once-daily portion and stop at what is eaten within a few minutes.
• Before any later addition: repeat the water checks and assess chasing, hiding and use of space.

New tank syndrome occurs when there are too few nitrifying bacteria to process the waste being produced. Ammonia and nitrite can then rise to harmful levels, causing illness or death. Slow stocking is therefore a water-quality decision, not merely a way to make observation easier.

Do not assume that clear-looking water is chemically safe. Ammonia and nitrite require testing, and filter bacteria are living populations whose capacity changes with the aquarium’s waste load. If either reading rises above zero, pause further additions and deal with water quality before continuing the stocking plan.

Healthy fish are described by OATA as having clear, bright eyes, undamaged fins, intact scales and no ulcerations or bumps. Continue checking those features after introduction. A change in appetite, breathing, position in the aquarium or temperament can be the first sign that water quality, social pressure or health needs attention.

Receive and acclimatise the fish carefully

Arrange for someone to receive the parcel in person, because live fish must not be left unattended, and follow the Tropical Fish Co delivery and Live Arrival Guarantee policy. Fish are hand-bagged in pure oxygen, placed in an insulated poly box and packed with a heat pack when the weather calls for it. A licensed live-animal courier carries the parcel, and tracking plus the confirmed delivery date are sent by email.

Follow the arrival sequence

1. Start filming before opening: show the parcel still sealed with the outer box visible, then record the opening and the fish inside the sealed bag in one continuous take.
2. Open and inspect it that day: keep the fish in the sealed bag while its condition is first recorded.
3. Float the bag: float the bag for 20–30 minutes before releasing the fish.
4. Keep bag water out of the aquarium: release the fish without pouring the transport water into the tank.

Prepare the aquarium before the parcel arrives. The water should already be at 22–27°C, pH 7.0–8.0 and 10–12 dGH, with ammonia and nitrite at zero. Complete these checks in advance so the fish can be released after acclimatisation without waiting for equipment or water adjustments.

The continuous video is required from the sealed parcel onward. Keep the order number with the recording. If anything has gone wrong, contact us the same day with the order number and video so the Live Arrival Guarantee process can be assessed promptly.

After release, observe swimming, breathing, colour, position and interest in food.

Plan the swordtail group before choosing companions

Begin with a plan for at least three swordtails. OATA says platies and swordtails require some companionship and suggests at least three, using two females to each male to reduce stress on females or other aquarium inhabitants. More can be kept where the same ratio and a larger aquarium are provided.

The ratio guides how the group is built over time. Do not judge the sex of the fish received from its dispatch size, gallery appearance or colour. Reassess the group against the two-females-to-each-male ratio before making later additions.

Plan around male rivalry

FishBase describes males as aggressive towards one another. Seriously Fish adds that males in confined spaces tend to establish dominance hierarchies and may invest substantial time maintaining their positions. This makes floor space, visual cover and group composition relevant whenever more than one male is present.

• If chasing is brief and fish retain access to the aquarium: continue observing how the group uses cover, swimming room and feeding areas.
• If one fish is repeatedly displaced: reassess group composition and usable space before adding any more livestock.
• If aggression rises as the group grows: check whether the aquarium still offers the required footprint, cover and open room.
• If the intended ratio cannot be maintained: pause further group expansion rather than relying on extra fish to settle the hierarchy.

Do not turn the suggestion of at least three into a fixed maximum or a guarantee of harmony. OATA permits larger groups when the aquarium is enlarged and the ratio is maintained, while Seriously Fish shows why confined space can intensify male social behaviour. The correct number therefore depends on the 120 × 30 cm starting footprint, any extra space, the observed sexes and the behaviour of the individuals.

Feeding and water quality also remain part of group management. Every additional fish increases feeding and waste, so increase numbers slowly and confirm ammonia and nitrite remain at zero. Social planning cannot compensate for an immature filter or an aquarium that is too small.

Screen every community companion

Screen companions for matching water, adequate adult space and tolerance of a lively swordtail. OATA describes platies and swordtails as generally peaceful and compatible with other species, but warns that large swordtails can be boisterous and may chase more timid tankmates. That is the central community decision for this form.

No universal list can account for the size, temperament and layout of every aquarium. Use the proposed companion’s own adult requirements, then compare them with 22–27°C, pH 7.0–8.0, 10–12 dGH and the space already needed by the swordtail group. A fish sharing the word “tropical” or belonging to another livebearer category still needs this full comparison.

Use a four-part screening rule

Treat male-to-male aggression as a separate risk from general community behaviour. A companion may meet the water and space checks while the swordtail group itself still needs adjustment. Conversely, a calm swordtail group does not make a timid companion automatically suitable.

Put any betta, guppy, tetra, cichlid, Corydoras, molly, danio or predatory fish through the four checks for its exact species and your aquarium before adding it.

For a stocking assessment, ask us with the aquarium dimensions, volume, measured water values, existing livestock and intended group size. Those details allow the decision to focus on the actual space and compatibility constraints rather than a generic community label.

Answer common buyer questions

How big does the Swordtail Marry Gold get?

It reaches 14 cm total length, so plan every dispatch size around a 14 cm adult.

What size aquarium does a Swordtail Marry Gold need?

Use a base of at least 120 × 30 cm or equivalent. Seriously Fish describes about 108 litres with those dimensions as the smallest aquarium to consider.

How many Swordtail Marry Gold should I keep together?

OATA suggests at least three swordtails, kept as two females to each male, and more can be added in that same ratio. Larger groups require more aquarium space.

Is the Swordtail Marry Gold suitable for beginners?

OATA describes most swordtails as easy to keep, but this fish still needs mature filtration, a 120 × 30 cm base, compatible water and weekly maintenance.

What does the Swordtail Marry Gold eat?

Feed a balanced omnivore diet of quality dried food plus small live or frozen Daphnia, Artemia, bloodworm or tubifex, once daily in an amount eaten within a few minutes.

What temperature and pH does it need?

Keep it at 22–27°C, pH 7.0–8.0 and 10–12 dGH, the shared overlap of FishBase, Seriously Fish and OATA guidance.

Is this fish aggressive?

Male swordtails can be aggressive towards one another, and large swordtails may chase timid tankmates. Screen for rivalry and chasing rather than relying on a simple temperament label.

Which kinds of animals can it live with?

OATA describes swordtails as generally compatible with other species. Choose peaceful companions with matching water and enough adult space, avoiding plans that expose timid tankmates to persistent chasing.

How is this fish packed and delivered in the UK?

Tropical Fish Co hand-bags it in pure oxygen, uses an insulated poly box and adds a heat pack when needed; a licensed live-animal courier carries the parcel.

Consult the public references

• FishBase: Xiphophorus hellerii identity, family, distribution, recorded environment, adult length, natural habitat, diet and male behaviour.
• Seriously Fish: aquarium footprint, volume, water conditions, filtration, heating, décor, diet, social behaviour and sexual dimorphism.
• OATA: practical care guidance for platies and swordtails, including companionship, water quality, feeding, maintenance and health observations.
• RSPCA: aquarium filtration, biological maturation and the conversion of ammonia through nitrite to nitrate.
• Tropical Fish Co delivery and Live Arrival Guarantee policy: packing, receipt, unboxing video and acclimatisation procedure.