Wakin Goldfish Care Guide: The Double-Tailed Pond Goldfish

Species Overview#

Wakin goldfish (Carassius auratus) are the original Japanese pond goldfish — a streamlined, double-tailed variety bred for centuries in temple ponds and koi gardens across Japan. They sit in a unique middle ground between the torpedo-shaped Comet and the egg-shaped fancy goldfish: a single, athletic body paired with a paired (split) caudal fin. The result is a fish that swims with the speed and stamina of a Comet but carries the ornamental tail symmetry that pond keepers prize in fancy varieties.

In Japan, the Wakin is so common that the name literally translates to "Japanese goldfish" — it is the default goldfish of Japanese culture, the equivalent of the Common goldfish in the West. Outside Japan, Wakin remain less well-known than their Comet and Shubunkin cousins, partly because they need slightly more deliberate sourcing. They are not a fragile show fish, though; they are arguably the most practical large pond goldfish you can stock outside of Koi.

Adult size

10-12 in (25-30 cm)

Lifespan

15+ years

Min tank

75 gal indoor / pond ideal

Temperament

Peaceful, active

Difficulty

Beginner-Intermediate

Diet

Omnivore

Origin: The Japanese "Common" Goldfish#

The Wakin descends from the original Chinese goldfish stock that arrived in Japan in the early 1500s. Japanese breeders kept the streamlined body of the wild ancestor while selecting for the double-tail mutation that had also produced the Ryukin and other Asian fancies. By the Edo period, the Wakin was the standard pond goldfish across Japan — a hardy, productive fish that could overwinter in unheated garden ponds and still spawn reliably each spring.

Most Wakin in the hobby today share that same robust genetic backbone. They were selected for survival in outdoor ponds, not for delicate ornamental traits, which is why they tolerate temperature swings, variable water quality, and high stocking density better than their fancy cousins. The closely related Watonai goldfish — a Wakin x Ryukin hybrid with longer flowing fins — shows up in some specialty stores and is worth knowing about as a Wakin alternative when finnage is the priority.

Distinguishing the Wakin: Double Tail vs. Single Tail#

The defining feature of the Wakin is the combination of a single, streamlined body with a double caudal fin. Look at the fish from above and you will see two distinct tail lobes splaying outward in a V — but the body itself is long and torpedo-shaped, with no humped back, no telescoping eyes, no wen, and a normal upright dorsal fin. This combination is rare and genuinely distinctive once you have seen it.

The most common color pattern is "Sarasa" — red-and-white in irregular patches, sometimes with a calico (blue-orange-black) overlay on higher-grade specimens. Solid red and solid white Wakin exist but are less popular than the bi-color form. A high-quality Wakin will have a symmetrical double tail (often called "tripod" or "butterfly" when viewed from above), an upright dorsal fin that does not droop, and clean, contrasting color blocks rather than smudged borders.

Expected Size and Lifespan#

Adult Wakin reach 10-12 inches with the tail included, with the body alone typically running 7-9 inches. Pond specimens often exceed the upper end of this range — 14-inch Wakin are not unusual in well-stocked outdoor ponds with multi-year residents. They grow noticeably faster than most fancy varieties because their streamlined body shape is more efficient for sustained swimming and active feeding.

Lifespan in a properly maintained pond reaches 15 years routinely, with documented specimens passing 20. Indoor tank lifespans tend to run shorter — 10-12 years is typical — primarily because tank-kept Wakin rarely get the swimming volume and seasonal cooling that triggers their natural metabolic rhythm. If you can pond them, do.

Water Parameters & Tank Requirements#

Wakin are cold-water fish bred for outdoor ponds. They will live in indoor aquariums, but only if the tank is large enough to accommodate their adult size and the filter is sized for their substantial waste output.

Minimum Tank Size vs. Pond Suitability#

Indoors, a single Wakin needs 75 gallons minimum, with another 30-50 gallons per additional fish. A pair belongs in a 125-gallon long tank; three or four fish need a 180-gallon footprint. As with the Comet, tank shape matters as much as gallonage — Wakin are sustained swimmers and need horizontal swimming length over tall display height. A 75-gallon "long" tank with 48 inches of swimming space outperforms a 90-gallon "tall" tank every time. For sizing different tank footprints, see our aquarium dimensions guide.

The honest answer for most Wakin keepers is a pond. A 300-500 gallon outdoor pond easily houses 3-4 Wakin to full size and gives them the seasonal temperature variation that triggers natural breeding behavior. Wakin are arguably the best pond goldfish below the size class of Koi — they are large enough to be visible from across a yard, hardy enough to overwinter, and active enough that you actually see them move around the pond.

Temperature Ranges: Cold-Hardiness and Overwintering#

Wakin thrive between 50 and 72 degrees Fahrenheit and tolerate brief excursions up to 85 degrees in summer ponds, provided dissolved oxygen stays high. They overwinter safely in ponds that do not freeze solid — a minimum pond depth of 30 inches gives them a thermal refuge below the ice line, and a de-icer or air stone keeps a hole in the ice for gas exchange during the coldest weeks.

Indoor tanks rarely need a heater for Wakin. Most home temperatures (65-72 degrees F) sit comfortably in the species' preferred range year-round. Stop feeding when pond temperatures drop below 50 degrees F — the fish's metabolism slows dramatically and undigested food will rot in their gut.

Filtration Needs#

Goldfish produce roughly 2-3 times the waste of comparably sized tropical fish (per SRAC Publication No. 4702 on goldfish production). Your filter needs to turn over the full tank volume 8-10 times per hour just to keep up. For a 75-gallon Wakin tank, that means a filter rated for 600-750 GPH — typically a canister filter (Fluval FX4, Eheim 2217) or a sump.

Pond filtration follows the same logic at a different scale. A 500-gallon pond needs a pressurized pond filter, a UV clarifier (to control algae blooms), and ideally a bog filter section planted with cattails or pickerel weed for nitrate uptake. Skip the bog at your own risk — Wakin produce enough nitrate to green-out a pond by midsummer without plant uptake.

For a baseline on parameters across the goldfish family, the freshwater fish overview covers the wider category context.

Diet & Feeding#

Wakin are opportunistic omnivores. In a pond they spend hours each day sifting through substrate, grazing algae off rocks, and picking insect larvae off plant stems. In an aquarium you replicate that variety with a mix of pellets, vegetables, and occasional protein treats.

High-Protein Pellets for Growth#

Sinking goldfish pellets should be the staple — not flakes. Pellets sink past the surface before the fish can gulp air, which prevents the swim-bladder problems that plague their fancy goldfish cousins. Look for a pellet with 30-35% protein, added spirulina or astaxanthin for color enhancement, and recognizable whole-food ingredients (fish meal, wheat germ, brewer's yeast).

Sinking wheat germ pellets are the standard cold-weather formula for Wakin. Wheat germ is more easily digested at lower temperatures and prevents the gut blockages that high-protein pellets can cause when the fish's metabolism slows in autumn. Switch to wheat germ when pond temperatures drop below 60 degrees F and discontinue feeding entirely below 50 degrees F.

Sinking vs. Floating Foods for Deep-Bodied Fish#

Stick with sinking foods exclusively for Wakin, even though their bodies are more streamlined than true fancy goldfish. The swim-bladder advantage of sinking pellets — no surface gulping — applies to any double-tailed goldfish, and it costs nothing to default to sinking food. Floating flakes are fine for Comets and Common goldfish; for Wakin, the small extra risk is not worth the convenience.

Fresh Greens and Foraging Behavior#

Blanched vegetables belong in the rotation. Shelled green peas (boiled 30 seconds, skin removed), thin slices of zucchini blanched and weighed down with a fork, and blanched spinach all provide fiber that prevents constipation. Vegetables should make up 20-30% of the overall diet for an adult Wakin.

Live and frozen treats — daphnia, brine shrimp, bloodworms — make excellent supplements 1-2 times per week. Daphnia is the safest live food because the exoskeleton acts as roughage. Feed 2-3 small meals per day in warm months, only what the fish consume in about 2 minutes per meal.

Tank Mates & Compatibility#

Wakin sit in the same swimming-speed category as Comets and Shubunkins — fast, sustained, competitive at feeding time. They share a temperature range with no tropical species. The tank-mate list narrows accordingly.

Best Matches: Shubunkins, Comets, and Sarasa Comets#

Other single-body, fast-swimming goldfish are the natural pairing. Shubunkins, Comet goldfish, Sarasa Comets, and other Wakin all share temperature, food, and space requirements, and they school comfortably together. Three to five Wakin in a properly sized pond develop noticeably more natural behavior than a single fish kept alone — they spawn, they forage in groups, they jockey for feeding position.

Weather loaches (Misgurnus anguillicaudatus) are the classic non-goldfish companion. They tolerate cool water, are peaceful, occupy the bottom of the pond or tank where Wakin spend less time, and grow to a similar 8-10 inch size that prevents them from being mistaken for food. Apple snails and large mystery snails work as cleanup crew in heated indoor tanks.

Why to Avoid Fancy Goldfish#

The same logic that excludes Telescope Eyes and Pearlscales from a Comet tank applies twice as hard to Wakin. The visual gap between an athletic Wakin sprinting across a pond and a wobbling Bubble Eye trying to navigate by feel is enormous. Pick one body type per pond — fast single-body or slow round-body — and stock accordingly. The Fantail goldfish guide covers the round-body alternatives if that is the route you would rather take.

Invertebrate Compatibility#

Apple snails (Pomacea bridgesii) and large adult mystery snails are too big to be eaten and help control algae. Cherry shrimp, dwarf snails, and small mystery snail juveniles will be eaten — Wakin treat anything that fits in their mouth as food, eventually. Stick to invertebrates that have outgrown the danger zone before introducing them.

Breeding Wakin Goldfish#

Wakin breed reliably in outdoor ponds across most of the continental US. They are one of the easier goldfish varieties to spawn at home because their hardiness lets them tolerate the temperature manipulation that triggers spawning behavior.

Triggering Spawning with Temperature Shifts#

The natural spawning trigger is a sustained spring rise from winter lows (45-55 degrees F) up through 65 degrees F over several weeks. Pond Wakin spawn on their own each spring without intervention; indoor breeders simulate the cycle by running tank temperature down to 55 degrees F over a month, holding it there for several weeks, then warming back to 65-68 degrees F to trigger the spawn.

Add spawning mops, fine-leaved plants (hornwort, cabomba), or yarn mops to the breeding tank or pond. Wakin scatter sticky eggs across vegetation, and the parents will eat any eggs they can find within hours of spawning. Remove the eggs (or the parents) within a day to keep the clutch.

Identifying Males and Females#

Sexually mature males develop white tubercles (small bumps) along the leading edge of the pectoral fins and across the gill plates during breeding season — these are the most reliable sex indicator. Females are usually rounder when full of eggs, but body shape alone is not definitive outside the breeding window.

Raising Fry: Culling for the Double-Tail Trait#

Wakin fry hatch in 4-7 days at 65-70 degrees F. Feed infusoria, then microworms, then baby brine shrimp as the fry grow. Within 6-8 weeks the survivors will show clear tail morphology — the iconic Wakin double tail in some, single Comet-style tails in others, and a range of intermediate forms. Serious breeders cull single-tailed fry early to maintain the double-tail trait in subsequent generations. Casual breeders can keep the mixed clutch and rehome the single-tail fry as Sarasa Comets.

Common Health Issues#

Most Wakin health problems trace directly back to water quality and outdoor pond exposure. Maintain stable parameters and a measured diet, and you will dodge 80% of the issues that send keepers searching for emergency advice.

Ich and Anchor Worms in Outdoor Settings#

Ich (Ichthyophthirius multifiliis) shows up as small white spots resembling salt grains across the body and fins, usually paired with the fish flashing or rubbing against decorations. Pond Wakin pick it up most often during temperature swings in spring and fall when the fish's immune system is stressed. Treat with aquarium salt at 1 tablespoon per 5 gallons (lower dose for ponds with sensitive plants), and raise tank temperature gradually to 75 degrees F if possible. Hold treatment for 10-14 days to break the parasite life cycle.

Anchor worms (Lernaea) are an outdoor-specific parasite — they look like small thread-like worms anchored to the fish's body, often near the base of fins. Treatment requires a dedicated anti-parasite medication (diflubenzuron or ivermectin-based products) and physical removal of visible worms with tweezers. New pond fish should always be quarantined and inspected for anchor worms before joining the main population.

Preventing Dropsy and Swim Bladder Issues#

Dropsy presents as raised scales (a "pinecone" appearance) and swelling, and it is almost always a symptom of advanced internal infection rather than a disease itself. Once dropsy is visible, the prognosis is poor — prevention through good water quality is the only reliable defense. Keep ammonia and nitrite at zero, nitrate below 20 ppm, and address any stress event (a botched water change, a tank-mate fight) before it cascades into infection.

Swim bladder issues are less common in Wakin than in fancy varieties because the streamlined body puts less pressure on the bladder. When they do occur, the trigger is usually overfeeding or floating-food gulping. Fast the fish for 24-48 hours and offer a single blanched, de-shelled green pea — the fiber resolves most cases within a day or two.

Where to Buy & What to Look For#

Wakin are not as common as Comets in chain pet stores, which is mostly a good thing. The Wakin you find at a dedicated local fish store or pond-specialty supplier is almost always a higher-quality specimen than the feeder-tank Comets sold by the bag.

Identifying High-Quality "Tripod" or "Butterfly" Tails#

Inspect the source tank carefully. A high-quality Wakin will have a symmetrical double tail when viewed from above — both lobes the same length, splaying outward at roughly equal angles. The "tripod" form has three visible tail divisions; the "butterfly" form has two clean lobes. Avoid specimens with one short tail lobe, a fused tail (which indicates incomplete double-tail genetics), or a tail held permanently to one side (often a sign of past injury or skeletal deformity).

The dorsal fin should stand fully upright, not droop or fold to one side. The body should be straight when viewed from above, with no curvature or visible kinks in the spine. Color blocks should be clean and contrasting — smudged or muddy color borders indicate either young fish that will improve with age or low-grade stock that will not.

Quarantining New Arrivals from Local Fish Stores#

Every new Wakin should spend 2-4 weeks in a separate quarantine tank before joining your display tank or pond. A bare-bottom 30-gallon tank with a sponge filter, an air stone, and prophylactic aquarium salt at 1 tablespoon per 5 gallons handles the job. Watch for ich, fin rot, and anchor worms during quarantine, and treat as needed before introducing the fish to the main system.

For acclimation method specifics that apply to goldfish moving from cooler shipping water to warmer pond water, see our acclimation guide. The drip method is preferred for Wakin because of how sensitive cold-water fish are to sudden temperature shifts.

Quick Reference#

• Tank size: 75 gallons minimum indoors for one fish, +30-50 gallons per additional; 300-500 gallon pond ideal
• Tank shape: Long footprint over tall — minimum 48 inches of swimming length
• Temperature: 50-72 degrees F (10-22 degrees C) — cold-water species, no heater needed in most homes
• pH: 7.0-8.0 | Hardness: 5-19 dGH | Ammonia/Nitrite: 0 ppm | Nitrate: under 20 ppm
• Filtration: 8-10x tank volume per hour; oversize by one tier; canister or sump preferred
• Diet: Sinking goldfish pellets (staple), wheat germ pellets in cool months, blanched vegetables, occasional frozen treats
• Feeding: 2-3 small meals daily in warm months, only what they eat in 2 minutes; stop feeding below 50 degrees F
• Tankmates: Other single-body goldfish (Comets, Shubunkins, other Wakin), weather loaches, large mystery snails
• Avoid: Fancy goldfish (Orandas, Ranchus, Telescope Eyes, Bubble Eyes), tropical fish, fin nippers, anything small enough to swallow
• Lifespan: 15+ years (some pond specimens 20+)
• Adult size: 10-12 inches including tail; body alone often 7-9 inches
• Quarantine: 2-4 weeks for any new fish, with anchor worm and ich treatment as needed
• Difficulty: Beginner-Intermediate — easy if ponded, demanding if kept in indoor aquarium