Real Longfin Medaka

Real Longfin Medaka key facts

Care level

Intermediate

Lifespan

2-3 years

Size

Up to about 4cm SL

Temperature

18〜28℃

Diet

Prepared medaka food, green water

Lighting

Because the fins grow larger while keeping their outline, viewing the fish from the side and checking the fin edge is the easiest way to judge the trait. Outdoors, summer sun raises water temperature sharply, so shade half the container with something such as a reed screen.

Diet & Nutrition

Commercial prepared medaka food is the staple, given in an amount finished within a few minutes. Leftovers decay and foul the water, so adjust the quantity. Green water rich in phytoplankton suits fry rearing.

Water Temperature & Quality

Slightly acidic to slightly alkaline water is considered ideal, and the water drifts toward acidic as keeping continues. Around one water change per week is the guideline, and because sudden shifts in temperature or pH cause stress, acclimatise new fish by floating the bag. FishBase records the wild water chemistry of this species as pH 7.0-8.0 and hardness 9-19 dH.

Tank Mates & Compatibility

Elongated fins are easily damaged by obstructions or crowding, so keep the container uncluttered and the stocking light. A peaceful schooling fish, normally kept as a group of the same variety. One litre of water per fish is the guideline against overcrowding; overstocking causes poor growth, reduced breeding, oxygen shortage and water fouling.

Breeding

Outdoors the spawning season runs from about April to October, once water reaches 18C or above with 12-13 hours of daylight. For year-round indoor breeding, 25-28C water and over 13 hours of lighting are the guideline. Eggs hatch at a cumulative 250 degree-days, about 10 days at 25C.

Health & Notes

Because every fin grows large, swimming power tends to drop, so avoid strong flow and overcrowding. Tell the trait from hirenaga by the shape of the extended part: a caudal fin that stays triangular is real longfin, while one with a short edge and a rounded outline is hirenaga. Outdoors the fish become inactive and overwinter near the bottom as water cools, resuming activity in spring once daytime water exceeds 10C. A 0.3-0.5% salt bath is used for ailing fish, with water raised to no more than about 28C.

About Real Longfin Medaka

A selectively bred medaka whose fins elongate to 1.5x their length while keeping their shape. Its triangular tail stays intact as it grows. Developed in 2020, it reaches about 4cm as an adult.

7 things to know before welcoming a Real Longfin Medaka

1. 1Triangular Tail Shape

   The Real Longfin Medaka's defining trait is a tail fin that keeps its triangular shape even as it grows larger — unlike earlier longfin strains, where fin growth is often uneven. It's a distinct look worth appreciating.

2. 2Avoid Sharp Decor

   The long, delicate fins can easily catch and tear on sharp ornaments or fine-mesh plant netting. Choose smooth, rounded decorations to keep the fins safe.

3. 3Choose Tankmates Carefully

   Fast-swimming fish or species that nip at fins can target the long fins as an easy mark. If keeping tankmates, pick calm, gentle species and watch how they interact.

4. 4Modest Swimming Power

   Larger fins mean somewhat weaker swimming ability than standard medaka. Strong currents can make it harder for them to reach food, so gentle filter flow works best.

5. 5Best Suited to Intermediate Keepers

   This variety is considered suited to intermediate keepers. Because fin damage or water quality issues can be easy to miss, some prior fishkeeping experience helps you catch problems early.

6. 6Pick by Tail Shape

   When choosing an individual, look for a tail that holds its clean triangular shape, without tears or cloudiness in the fins. Study photos and listing details closely before deciding.

7. 7Acclimate Slowly

   Sudden shifts in temperature or water chemistry can stress the delicate fins, so take your time acclimating new arrivals. Give them a calm environment while they settle in.

Frequently asked questions about Real Longfin Medaka

Q.How does it differ from other longfin medaka?

A.Standard longfin medaka often grow unevenly, but the Real Longfin Medaka's fins all elongate to over 1.5 times their length while keeping their shape — most notably, the tail fin stays triangular even as it grows.

Q.Is this variety suitable for beginners?

A.It's generally considered a variety for intermediate keepers. Because it needs some attention to fin condition and water quality, prior fishkeeping experience helps you care for it confidently.

Q.What happens if the fins get torn?

A.Torn or damaged fins often heal gradually as long as water quality is kept in good condition. Avoiding sharp decorations and watching tankmates closely helps prevent further damage.

Q.How big does it get?

A.Adults reach about 4cm in standard length at most. Its compact size makes it manageable even in smaller tanks.

Q.Can it be kept with other medaka?

A.It can be kept with calm, gentle tankmates, but fish that nip at fins may damage its long fins. Watch how tankmates interact and separate them if needed.

Useful tools for Real Longfin Medaka care

Learn more about Real Longfin Medaka in the encyclopedia

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