--- type: species title: "Black Moor Goldfish: Complete Care Guide for Beginners" slug: "black-moor-goldfish" category: "freshwater" scientificName: "Carassius auratus" subcategory: "Fancy Goldfish" lastUpdated: "2026-04-24" readingTime: 10 url: https://www.fishstores.org/species/black-moor-goldfish --- # Black Moor Goldfish: Complete Care Guide for Beginners *Carassius auratus* Learn how to care for black moor goldfish — tank size, water temp, diet, tank mates, and health tips for this popular fancy goldfish. The black moor (*Carassius auratus*) is the velvet-black, googly-eyed fancy goldfish almost every fishkeeper recognizes on sight. Those protruding telescope eyes give the fish its silhouette and its biggest care challenge — black moors see poorly, swim slowly, and bump into anything sharp. Get the tank setup right and a black moor will reward you with 10 to 15 years of slow, deliberate browsing through your aquarium. Get the tank mates wrong and a single comet goldfish will starve your moor inside a month. This guide focuses on the moor-specific details — telescope-eye protection, color shifts to bronze, and safe stocking choices — that the broader [fancy goldfish care guide](/guides/fancy-goldfish-guide) does not have room to cover at this depth. ## Species Overview Black moors are domesticated *Carassius auratus* selectively bred for two specific traits: a deep velvet-black coloration over a rounded fancy-goldfish body, and protruding "telescope" eyes that extend outward from the skull on short stalks. Strip away those two features and the underlying fish is the same species as a common goldfish — same family, same diet, same waste output, same lifespan ceiling. Every black moor you see in a store is a centuries-old domestication product, not a wild fish. | Field | Value | | -------------- | ------------------- | | Adult size | 6-8 in (15-20 cm) | | Lifespan | 10-15 years | | Min tank | 20 gallons (1 fish) | | Per added fish | +10 gallons | | Temperature | 65-72 degrees F | | Difficulty | Beginner | ### Appearance and the Telescope Eye Trait The telescope eye is the defining feature. Fry hatch with normal-set eyes; the eyes begin to extend outward between 6 and 12 months of age and reach full protrusion by year two. In a healthy adult, each eye sits on a short stalk that holds the eyeball roughly 5 to 10 mm out from the skull. The pupils stay forward-facing, but the field of view is far narrower than a normal goldfish. Most black moors are functionally near-blind to anything outside a few inches in front of them, navigating by smell and water vibration as much as by sight. Body shape is the standard fancy goldfish profile — short, deep, and egg-shaped, with paired (double) caudal and anal fins that should fan symmetrically when viewed from behind. The fins are typically long and flowing, often described as veiltail or broadtail depending on bloodline. Color is a deep matte black across the body, fins, and head. Quality moors have an even, velvety finish; lower-grade fish often show patchy areas where the black has thinned to bronze. The black coloration sits on top of an orange or bronze underlayer. As the surface black pigment fades — which happens in nearly every moor eventually — the underlying color shows through. A mature moor may keep a fully black face, develop bronze patches along the flanks, or transition to a solid orange "goldfish-colored" fish over the course of several years. None of this is disease. It is the natural pigment behavior of the variety. ### Size and Lifespan Black moors reach 6 to 8 inches body length within 3 to 5 years of growth, with exceptional pond-raised specimens occasionally exceeding 8 inches. The double tail and trailing fins add visible bulk on top of that body length without adding much weight. Lifespan is 10 to 15 years with proper care, and well-kept moors have been documented past 20. The single biggest predictor of lifespan is tank size during the first two years of growth. Fish kept in undersized tanks during the juvenile phase end up stunted, with compressed organs and a typical lifespan of 3 to 5 years rather than 15. Buying a 1-inch moor at the pet store and keeping it in a 5-gallon tank is the most common cause of premature goldfish death — not disease, not parasites, just bioload and growth restriction over time. Pond-raised moors sometimes outgrow aquarium specimens by 1 to 2 inches because the open swimming environment supports better long-term growth. Whether ponds are appropriate for moors specifically is covered later in the tank-setup section. ### Origin and Selective Breeding History Goldfish domestication began over a thousand years ago in Song Dynasty China, where wild *Carassius auratus* populations occasionally produced color mutations. Buddhist monks isolated and bred these fish in ponds, and by the Ming Dynasty, distinct fancy varieties with double tails and exaggerated features had emerged. The telescope-eye trait appeared in Chinese pond stock around the early 1700s, and the all-black version — the moor — was refined further in Japan, where breeders selected for the deepest, most consistent black coloration. The variety reached Europe and North America in the 1800s and has remained one of the most popular fancy goldfish varieties ever since. There is no "wild moor" to reference for natural water parameters. Care guidance comes from the species' close relative — the wild Prussian carp (*Carassius gibelio*) of cool, slow-moving rivers and ponds across temperate Eurasia — combined with several centuries of accumulated keeper knowledge. ## Water Parameters and Tank Requirements Black moors are cold-water fish with a heavy bioload, fragile telescope eyes, and limited swimming ability. Every tank decision should account for those four facts. ### Ideal Water Parameters Black moors thrive at 65 to 72 degrees F, with brief tolerance from 50 to 78 degrees. They do not need a heater in most US homes — room temperature is usually right in the target range. Sustained temperatures above 75 degrees F accelerate metabolism, increase oxygen demand, and shorten lifespan. Warm water also speeds the fade from black to bronze, which is one reason show breeders keep their moors at the cool end of the range. Target pH 7.0 to 7.4 with general hardness between 5 and 19 dGH. Goldfish tolerate moderately alkaline, hard water exceptionally well — better than they tolerate soft, acidic conditions. Ammonia and nitrite must read 0 ppm at all times; any detectable level damages gill tissue and stresses the immune system. Keep nitrate below 20 ppm with weekly 25 to 30 percent water changes. Fully cycle the tank (zero ammonia, zero nitrite, measurable nitrate) before adding any moor — uncycled tanks kill more goldfish than every disease combined. ### Minimum Tank Size and Stocking A single black moor needs a 20-gallon tank as the practical minimum, with 10 gallons added per additional fancy goldfish. A pair of moors does well in 30 gallons; a group of four needs 50 gallons. The fancy-goldfish community has shifted upward on tank size recommendations over the last decade as the negative effects of stunting have become better documented. Tall tanks (column, hex, or cube designs) are poor choices. Moors use horizontal swimming space and surface area for gas exchange, neither of which a tall narrow tank provides. A 20-gallon long (30 by 12 by 12 inches) outperforms a 20-gallon high or any tall column for this species. Use the [aquarium dimensions guide](/guides/aquarium-dimensions) to compare footprint options before you buy. Avoid putting black moors in outdoor ponds. Their poor vision makes them easy targets for predators — herons, raccoons, and outdoor cats all take advantage of fish that cannot see them coming. Their delicate eye stalks are also vulnerable to scrapes from rough pond surfaces and submerged debris. The [freshwater fish overview](/guides/freshwater-fish) covers indoor versus outdoor stocking choices in more depth. ### Filtration and Oxygenation Black moors produce two to three times the waste of comparably sized tropical fish. Your filter should turn over the tank volume at least 8 to 10 times per hour. For a 30-gallon tank, that means combined filtration rated for 240 to 300 GPH. Canister filters and oversized hang-on-back units work well; sponge filters are useful as supplemental aeration but cannot handle the bioload alone on a moor tank. Surface agitation is critical for oxygen exchange. An air stone or a return spray bar that ripples the surface keeps dissolved oxygen high enough to support the heavy gill workload of a fancy goldfish. What you should *not* do is run aggressive flow across the tank. Strong currents push moors into glass and decor, exhaust their slow-bodied swimming muscles, and most importantly can damage the protruding eyes. Use a spray bar, a flow deflector, or a low-flow filter outlet to spread current across the surface rather than blasting it through the swimming zone. Many moor keepers run their HOB filter output against the back glass to break the current before it reaches the fish. ### Substrate and Decor Considerations Smooth substrate only, and rounded decor only. A black moor's telescope eyes are essentially defenseless — a single sharp gravel edge or a jagged ornament corner can scratch the cornea, puncture the eye stalk, or trigger a bacterial infection that takes weeks to clear. This is the single most common preventable injury in the variety. > **Eye-bumping is a constant risk** > > Telescope-eye varieties cannot see what is directly in front of them. They will bump into glass, decor, and tank mates as part of normal foraging. Sharp gravel, jagged ornaments, plastic plants with hard edges, and any decoration with mold seams or rough castings can all cut the eye or eye stalk. A scratched eye leads to cloudiness, then to pop-eye, and often to permanent blindness in that eye if not caught early. Scan every piece of decor with your fingertip before adding it to a moor tank — if it would scratch your skin, it will scratch the fish. Acceptable substrate options include polished river gravel (under 3 mm or over 8 mm — the in-between size can lodge in the mouth), pool filter sand, or a bare bottom. Many serious moor keepers use bare-bottom tanks because they are easier to siphon clean, which matters when the bioload is this high. For decor, stick with smooth river stones, rounded ceramic caves, silk plants (not plastic), and broad-leaved live plants like anubias and java fern. Avoid plastic plants with hard, jagged leaves, fake corals, ceramic ornaments with mold seams, sharp driftwood, and anything else with edges or splinters. Dim lighting also helps — bright lighting stresses moors and can accelerate the bronze color shift. > **Bright light fades the black to bronze or orange** > > The deep black coloration of a moor sits on top of an underlying orange or bronze layer, and bright lighting accelerates the gradual fade. If you want to preserve the black as long as possible, keep tank lighting subdued (5 to 7 watts of LED for a 20-gallon, no direct sunlight on the tank), keep water temperatures at the cool end of the range (65 to 68 degrees F), and feed a balanced diet without excessive carotenoid supplements. Most moors will eventually shift to some bronze or orange regardless — this is genetic and not preventable. ## Diet and Feeding Diet directly affects swim bladder health, color quality, and growth rate. Get this right and you prevent the most common fancy goldfish problem before it starts. ### What Black Moors Eat **Sinking pellets** should be the daily staple. Floating pellets force the fish to gulp at the surface, ingesting air that contributes to swim bladder problems in round-bodied fancies. Hikari Lionhead, Saki-Hikari Fancy Goldfish, and Repashy Super Gold are all widely used by experienced moor keepers, with sinking textures specifically formulated for slow-eating fancy varieties. Pre-soak pellets in tank water for 30 to 60 seconds before dropping them in — this hydrates the food before it expands inside the fish, further reducing bloat and swim bladder strain. **Blanched vegetables** belong in the rotation 1 to 2 times per week. De-shelled peas, blanched zucchini slices, and blanched spinach all provide fiber that keeps the goldfish digestive tract moving. Peas in particular are the classic remedy for a constipated or floating moor. **Live and frozen foods** — daphnia, brine shrimp, and bloodworms — work as treats once or twice a week. Daphnia is especially useful because the chitin exoskeleton acts as digestive roughage. Drop them near the moor rather than in the open tank; with poor vision, the fish needs the food to land within smell range, not on the far side of the substrate where faster tank mates can grab it first. ### Feeding Schedule and Portion Size Feed 2 to 3 small meals per day, offering only what the fish can consume in about 2 minutes per feeding. Black moors are perpetually hungry and will beg convincingly — ignore them. Overfeeding is far more dangerous than underfeeding for this species, both because of the swim bladder risk and because uneaten food rots quickly in a high-bioload tank. Fast the fish one day per week. A weekly fast clears partially digested food from the gut, prevents constipation, and gives the swim bladder a chance to reset. Most experienced fancy goldfish keepers fast on the same day each week, often the day before a water change. Drop food in the same spot every time. A near-blind moor learns the feeding location quickly and will gather there at meal times. Scattering food across the tank surface just feeds whichever tank mates can see fastest. ## Tank Mates and Compatibility Black moors are peaceful, slow, and visually impaired by their telescope eyes — three traits that narrow the compatible-tankmate list considerably. ### Best Compatible Tank Mates The best moor tankmate is another fancy goldfish of similar swimming ability and vision. Good pairings include other black moors, telescope eyes (the non-black version of the same body type), bubble-eye goldfish, [oranda goldfish](/species/oranda-goldfish), and [ranchu goldfish](/species/ranchu-goldfish). The shared traits — slow speed, double tails, similar body shape, limited vision — mean nobody outcompetes anyone at feeding time. Pairing a moor with a [bubble-eye goldfish](/species/bubble-eye-goldfish) or another telescope variety is particularly natural because both fish navigate by smell and vibration. They feed at the same pace, swim at the same speed, and do not startle each other with sudden movements. This is the classic "vision-impaired tank" setup that fancy goldfish specialists recommend for first-time moor keepers. Beyond other fancies, dojo loaches (weather loaches, *Misgurnus anguillicaudatus*) are the classic non-goldfish companion. They tolerate cold water, are peaceful, occupy the bottom of the tank, and clean up uneaten food. Hillstream loaches and white cloud mountain minnows can also work in cooler moor tanks. Large mystery snails (*Pomacea bridgesii*) are safe — too big to eat and helpful for cleaning algae. > **Never house moors with single-tail goldfish** > > Common goldfish, comet goldfish, and shubunkins are dramatically faster, more aggressive feeders than any fancy variety. A black moor cannot compete — the single-tails will reach every meal first, and the moor will slowly lose weight even with plenty of food going into the tank. This is the single most common preventable mistake new moor keepers make. Keep moors in fancy-only tanks. If you want a comet, set up a separate pond or larger tank for it. Do not mix the two. ### Species to Avoid Tropical fish are an automatic no — their preferred temperature range (76 to 82 degrees F) is significantly higher than the moor's, and trying to compromise at 74 degrees stresses both groups long-term. This rules out bettas, tetras, gouramis, most cichlids, and most catfish. Tiger barbs, serpae tetras, and other known fin nippers will shred long moor fins. Crayfish and other large invertebrates will grab a slow-moving moor by the tail. Pufferfish will nip at the eyes. Small invertebrates (cherry shrimp, small ramshorn snails) become snacks. Common plecos (*Pterygoplichthys*) are not appropriate; they grow over a foot long, prefer warmer water, and have been confirmed to attach to goldfish slime coats at night. Anything fast, aggressive, or small enough to swallow does not belong in a moor tank. ## Common Health Issues Most black moor diseases trace back to one root cause: poor water quality. Fix the water first, then address symptoms. The two species-specific issues — eye injuries and swim bladder disorder — both have prevention strategies that beat treatment every time. ### Eye Injuries and Infections The telescope eye is the most vulnerable structure on a black moor. A scratched cornea, a punctured eye stalk, or a bacterial infection of the protruding eye tissue can all happen from a single bump on sharp decor. Symptoms to watch for: cloudiness over one or both eyes, white film on the eye surface, swelling around the base of the eye stalk (often called "pop-eye"), red weeping or visible blood streaking, or the eye sitting at an unusual angle compared to the other side. Mild cloudiness is usually a water quality issue — a 50 percent water change with dechlorinated, temperature-matched water often resolves it within a few days. Visible scratches or persistent cloudiness need active treatment. An aquarium salt bath (1 tablespoon per 5 gallons in a hospital tank, gradually raised over 24 hours) handles minor abrasions and prevents secondary infection. For visible bacterial infection (cloudy eye with redness or pus), a broad-spectrum antibiotic like Maracyn 2 or Kanaplex is the standard treatment. Severe pop-eye, ruptured eye stalk, or puncture wounds require an aquatic veterinarian. A moor can survive with one functional eye or even no functional vision — they navigate by smell and water vibration well enough to feed and behave normally — but the open wound must be closed and infection prevented during healing. ### Swim Bladder Disorder Swim bladder disorder is the signature ailment of fancy goldfish, and moors are particularly susceptible because their compressed body shape puts physical pressure on the swim bladder. Symptoms include floating sideways, sinking nose-down to the bottom, swimming in tight loops, or floating belly-up but otherwise alive and alert. The standard treatment protocol: fast the fish for 24 to 48 hours, then offer a skinned, blanched pea (the fiber gets the digestive tract moving). Lower the water level temporarily so the fish does not have to fight to reach the surface. If symptoms persist beyond 4 to 5 days, bacterial infection of the swim bladder may be the underlying cause — a course of broad-spectrum antibiotics is the next step. Prevention beats treatment. Sinking pellets only (never floating), 2-minute feeding limits, weekly fasting, pre-soaked food, and stable water temperatures are the five interventions that prevent most cases. Chronic, recurring swim bladder issues in fancy goldfish are often genetic and may not be fully correctable. ### Ich, Fin Rot, and Velvet **Ich** (*Ichthyophthirius multifiliis*) presents as white salt-grain spots on the body and fins, often paired with flashing (rubbing against decor) and clamped fins. Treatment: gradually raise tank temperature to 78 degrees F over 2 to 3 days, dose aquarium salt at 1 tablespoon per 5 gallons, and complete a full 14-day treatment cycle to break the parasite life cycle. Black moors tolerate the temperature increase well, but watch for accelerated color fade during treatment. **Fin rot** appears as ragged, fraying fin edges, often with a white or red margin. It is almost always caused by poor water quality, a recent injury, or chronic stress. Fix the water parameters first — a 50 percent water change immediately — then treat with a broad-spectrum antibiotic if the rot does not improve within a week. Long moor fins are especially prone to fin rot, so prevention through clean water beats treatment every time. **Velvet** (*Oodinium*) presents as a fine gold or rust-colored dust over the body, often only visible in side lighting. It is less common than ich but more dangerous when it appears. Treat with copper-based medication in a quarantine tank and dim the lighting (the parasite needs light to complete its life cycle). Always quarantine new fish before adding them to your display tank. Every new black moor should spend 2 to 4 weeks in a separate quarantine tank before joining your display. A bare-bottom 10-gallon with a sponge filter and air stone is sufficient. Observe for signs of disease, treat prophylactically with aquarium salt (1 tablespoon per 5 gallons), and monitor appetite and behavior. This step prevents introducing ich, flukes, or bacterial infections to an established tank. ## Breeding Black Moor Goldfish Black moors can be bred in the home aquarium, but show-quality breeding is a different commitment than casual spawning. ### Sexing and Spawning Conditions Mature moors (2+ years) are sexable during breeding season. Males develop small white tubercles (breeding stars) on the gill covers and leading edges of the pectoral fins — they look like tiny white salt grains. Females become noticeably rounder when carrying eggs (gravid), with a slight asymmetry visible from above as the body fills with eggs. Outside of breeding season, sexing is difficult by external features alone. Many keepers buy a group of 4 to 6 juveniles and assume mixed sexes will sort themselves out. Trigger spawning with a winter cool-down. Lower the tank temperature to 50 to 55 degrees F for several weeks (mimicking winter), then gradually warm to 68 to 72 degrees F over a week or two. The temperature rise triggers spawning behavior — males chase females, nudging the abdomen to release eggs, which are then immediately fertilized. Provide spawning mops or fine-leaved live plants (java moss works well) for the eggs to adhere to. A separate breeding tank is strongly recommended; adults will eat the eggs immediately if not separated. ### Egg and Fry Care Eggs hatch in 4 to 7 days at 70 degrees F. Move the spawning mop to a separate hatching tank as soon as spawning ends. Fry are tiny and emerge brown or olive-colored — not black. The melanin that gives adult moors their velvet coloration takes 3 to 6 months to develop, and the telescope eye trait takes even longer (6 to 12 months for the eyes to begin protruding). You cannot select for black coloration or eye quality in the early fry stage. Quality breeders often wait 6 to 12 months before culling for body shape, color, and eye development. First foods are infusoria or commercial liquid fry food for the first week, then progress to baby brine shrimp and crushed flake. Growth is fast in the first 3 months and then slows. Survival rate from egg to 6-month juvenile is typically 10 to 30 percent in home setups, much higher in dedicated breeding ponds. ## Where to Buy and What to Look For Healthy black moors start with a healthy source. Where you buy matters as much as what you buy. ### Selecting a Healthy Fish at Your Local Fish Store Visit the store, observe the moor tank for at least 5 to 10 minutes, and run through this checklist before asking staff to bag anything: - **Active, upright swimming** — no listing, no floating sideways, no sitting on the substrate. - **Clear, bright eyes with no cloudiness** — both eyes should look identical in shape and size, with no white film or visible scratches. - **Both eye stalks intact and symmetrical** — a moor with one missing or damaged eye is a fish that has already had a serious injury. - **Intact, unfrayed fins** — no ragged edges, no white spots, no blood streaking. - **Smooth, flat scales** — no raised scales (raised scales indicate dropsy, which is often fatal). - **Even, deep black coloration** — some bronze fade is normal in older moors, but a young pet-store fish should be near-uniformly black. - **No flashing or scratching** against decor or substrate. - **Tank water is clean and clear** — no ammonia smell, no visible debris on the bottom. - **No dead or visibly sick fish** in the same tank or shared filtration system. Ask staff how long the fish have been in the store (newly arrived shipments are still stressed), whether new arrivals are quarantined, and what the fish are currently being fed. A knowledgeable shop will answer confidently. Vague or dismissive responses are a red flag. > **Inspect black moors in person before buying** > > Pet store and big-box chain moor quality varies widely. A dedicated local fish store with knowledgeable staff is far more likely to stock fish from a quality source, hold them in proper cold-water conditions, and quarantine new arrivals. Spend the extra dollars on a healthy fish from a good shop — a stunted or sick moor from a bad source will cost more in time, medication, and grief. ### Price Range and What to Expect Common pet-store black moors run $5 to $20 depending on size, with 2 to 3 inch juveniles at the low end and 4 to 6 inch grown specimens at the high end. Show-quality moors from specialty breeders — particularly Thai, Chinese, or Japanese imports with deep pigmentation, perfect eye symmetry, and strong body shape — can run $50 to $200 or more. For your first moor, a healthy $10 specimen from a clean local fish store will bring more lasting joy than a $100 show fish that arrives stressed from overnight shipping. Save the import-quality breeders for your second or third fish, when you have established water and a working quarantine routine. Acclimation should be drip-style over 60 to 90 minutes for shipped fish, or float-and-add over 30 minutes for short-distance LFS purchases. Always use a quarantine tank for 2 to 4 weeks before adding a new moor to an established display. ## Quick Reference - **Tank size:** 20 gallons for one moor, +10 gallons per additional fancy goldfish - **Temperature:** 65-72 degrees F (no heater needed in most homes; cooler end preserves black color) - **pH:** 7.0-7.4 | **Hardness:** 5-19 dGH - **Ammonia/Nitrite:** 0 ppm | **Nitrate:** under 20 ppm - **Filtration:** 8-10x tank volume per hour, low-flow output, surface agitation for oxygen - **Substrate:** Smooth river gravel, sand, or bare bottom — never sharp gravel - **Decor:** Rounded, smooth-edged only; no plastic plants with hard edges, no jagged ornaments - **Lighting:** Subdued (5-7 watts LED for a 20-gallon); bright light accelerates color fade - **Diet:** Sinking pellets (Hikari Lionhead, Saki-Hikari, or equivalent), pre-soaked, plus blanched veggies and occasional frozen treats - **Feeding:** 2-3 small meals daily, 2-minute rule, fast one day per week - **Tankmates:** Other slow fancy goldfish (other moors, telescopes, bubble eyes, orandas, ranchus), dojo loaches, mystery snails - **Avoid:** Single-tail goldfish (commons, comets, shubunkins), tropical fish, fin nippers, sharp decor, outdoor ponds - **Eye care:** Smooth tank only, watch for cloudiness or pop-eye, treat injuries with salt baths or antibiotics - **Color:** Black fades to bronze or orange with age, warmth, and bright light — this is genetic, not disease - **Lifespan:** 10-15 years (some over 20 with optimal care) - **Adult size:** 6-8 inches body length plus trailing fins - **Quarantine:** 2-4 weeks for every new fish, no exceptions For broader fancy goldfish context — variety comparisons, pond suitability, and cross-variety stocking — see the [fancy goldfish care guide](/guides/fancy-goldfish-guide), which is the canonical parent reference for this species family. ## Frequently Asked Questions ### How big do black moor goldfish get? Black moors typically reach 6-8 inches in a properly sized tank with good water quality. Some well-fed specimens in large ponds can exceed 8 inches. Stunted growth is common in tanks that are too small or overcrowded. ### Can black moor goldfish live with tropical fish? No. Black moors thrive at 65-72 degrees F, which is too cold for most tropical fish. Mixing them with species like bettas or tetras causes chronic stress for one or both fish and increases disease risk. ### Why is my black moor goldfish turning orange? Color change from black to bronze or orange is common and caused by genetics, age, or warmer water temperatures. It is not a disease. Some fish partially retain black coloration; others turn fully orange or gold over time. ### How often should I feed my black moor goldfish? Feed 2-3 small meals per day, offering only what the fish consumes in about 2 minutes. Overfeeding causes water quality problems and swim bladder issues. Sinking pellets are preferred over floating flakes to reduce air ingestion. ### What tank size does a black moor goldfish need? A single black moor needs a minimum 20-gallon tank. Add at least 10 gallons for each additional fancy goldfish. Goldfish produce significant waste, so larger tanks with strong filtration are always better for long-term health. --- *Source: [FishStores.org](https://www.fishstores.org/species/black-moor-goldfish)* *Last updated: April 24, 2026*