Koi Fry Rearing Protocol Guide: Day 1 to Tategoi
The journey from a 1.5 mm koi egg to a tategoi candidate worth keeping involves brutal arithmetic — a single spawn produces 100,000+ eggs, and most breeders cull 95-99 per cent of the resulting fry over the first six months. The koi fry rearing protocol decides which percentage of those fish make it into the next selection round, and the choices made in weeks one through twelve permanently shape body conformation. This guide from Gensou Aquascaping at 5 Everton Park walks through hatching, first foods, culling milestones and the tategoi selection cascade.
Hatching and First 72 Hours
Eggs hatch 4-7 days post-spawn at 22-25°C. Newly hatched fry attach to brushes via head adhesive glands and consume their yolk sacs over 48-72 hours. Maintain temperature stability and avoid disturbance during this window. Aeration runs low; no filtration intake near the fry mass. Once swim-up begins (fry detach and swim to the surface to gulp air for the swim bladder), feeding starts immediately or starvation kicks in within 12 hours.
First Feed: Infusoria and Brine Shrimp
Day 1 of free swimming: feed cultured infusoria (paramecium, rotifers) at 4-hour intervals. Cultures take 7-10 days to ramp up, so start the culture during egg incubation. Day 4-5: introduce newly hatched brine shrimp (Artemia) — hatched daily from cysts in 28°C salt water. Brine shrimp drives growth rates dramatically. Continue brine shrimp until day 30 alongside other foods.
Transitioning to Powdered Feed
From day 14, supplement with crumbled koi fry powder (Hikari First Bites or Saki-Hikari Multi Stage at SGD 25-50 per 100 g from the fish food and feeding range). By day 30, fry transition to crushed pellet (1 mm). Feed 6-8 small portions daily during peak growth months. Water quality must stay pristine — ammonia or nitrite kills fry within hours.
Pond and Water Management
Run the fry pond at 30-50 cm depth, 25-28°C, with sponge-baffled or air-driven sponge filtration only. Strong mechanical filtration sucks up fry. Daily 10-20 per cent water exchanges at temperature-matched parameters. Keep pH 7.2-7.6, KH 4-6, ammonia and nitrite zero. Use kit from the aquarium equipment range for sponge filters and air pumps. Treat water with conditioner from the water care and treatment shelf.
First Cull at Day 30
By day 30, fry reach 2-3 cm. The first cull removes deformities (bent spines, missing eyes, fused fins), albinism (unless target variety), and obvious finnage failures. Expect to cull 50-80 per cent of remaining fry depending on the parent cross. Use a fine net and shallow viewing tray. Discarded fry go to bait fish dealers or are humanely euthanised — never released into local waterways. The remaining 20-50 per cent advance.
Second Cull at Day 90
Around month three, fry reach 5-8 cm. The second cull selects on body shape (fukutan — torpedo body), pattern emergence, and skin quality. Pattern shows clearly by 6-8 cm in most varieties. Cull 70-90 per cent at this stage — keep only fish with potential body conformation, balanced patterns, and clean kiwa edges. Pearlscale, dragonscale, and hi distribution are now visible.
Final Cull at Month Six
Around month six, fish reach 12-18 cm. The third cull is the harshest — selecting tategoi candidates means keeping 1-5 per cent of original fry. Body conformation, skin luster, hi quality, sumi development (in utsuri/showa lines), and pattern balance all weigh together. The retained tategoi go into grow-out ponds for the next 12-18 months. The remainder enter the wholesale or retail channels at SGD 30-200 per fish.
Common Fry Losses
Major risks during the first six months: ammonia spikes (most common cause of mass die-off), fungal infections on weak fry, predation by introduced wild dragonfly larvae and frogs, and temperature swings during monsoon. Cover the fry pond with mesh against predators. Test water daily. Maintain consistent temperature with a chiller or heater backup if pond is exposed.
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