Tail Genetics
The tosakin tail results from a rare recessive gene that causes the caudal fin to fan horizontally rather than vertically. The tail edges also curl back toward the head.
Breeding true tosakin requires both parents to carry the gene. Only 30-40% of fry show correct tail form even from proven pairs.
Viewing Bowl Tradition
Tosakin are shown in round wooden "tarai" bowls 60-80cm wide, 15cm deep. The shallow water forces the tail to spread fully on the surface.
Keeping them long-term in deep tanks causes tail deformity. Rotate to the bowl monthly for proper development.
Care Requirements
Water must be clean but current should be gentle. Strong filtration deforms the delicate curled tail edges.
Keep alone or with other tosakin. Other fancy goldfish can nip the tail and ruin show quality.
Cost and Availability
Show-grade tosakin from Kochi Prefecture can cost 200-2000 USD per fish. Hobby grade exports are rare outside Japan.
In Southeast Asia, expect 100-400 USD for a decent specimen. Always quarantine imported fish for 4 weeks.