Yearling Goldfish (Tosai)—Where Breeder Skill Is Most Tested
"Tosai" refers to goldfish born in the current year. During the six months to one year following hatching, each individual's lifelong body shape, fin form, and color characteristics are established. Proper selection and rearing of yearlings is the core technique that separates serious goldfish breeders, producing future exhibition-quality individuals and superior breeding stock.
Raising thousands to tens of thousands of hatched yearlings to exhibition standards requires multiple selection rounds (culling). By properly managing selection criteria and rearing environment, you can efficiently develop a small number of high-quality individuals.
Selection Timing: Three Rounds of Culling
Yearling selection typically proceeds through multiple culling rounds as the fish grow.
First Selection: Fry Stage (2–3 weeks post-hatch)
Initial culling occurs when fry reach approximately 1.5–2 cm.
Fish to remove (inferior individuals):
- Curved or bent spine
- Severely stunted growth (marked size disparity)
- Deformed or missing fins
- Abnormal swimming (inversion, one-directional circling)
At this stage, final body-shape assessment is premature; the primary goal is removing obviously malformed and weakly individuals.
Second Selection: Juvenile Stage (6–8 weeks post-hatch, 3–5 cm)
The most critical culling round. Breed-specific traits now become visible (ranchu head-mass development begins; oranda dorsal-fin formation appears, etc.).
Evaluation points (weights vary by breed):
| Evaluation Item | Good Individual | Remove |
|---|
| Body shape | Wide body, compact and well-proportioned | Elongated, asymmetrical |
| Tail fin | Correct tail form per breed (four-lobed, three-lobed, cherry-blossom, etc.) | Collapsed tail form, tangled tail |
| Belly | Symmetrical roundness when viewed from below | Uneven, dented |
| Overall balance | Good head–body–tail proportion | Unbalanced |
Ranchu-specific evaluation:
- Head: Lateral silhouette should be straight (no backwards curve)
- Head: Dorsal peak should sit behind the body's midpoint
- Dorsal-less (no dorsal fin): Confirm complete absence
- Tail angle: 90 degrees or greater, spreading horizontally
Third Selection: Late Summer–Autumn (8–10 cm)
Color development completes, and final exhibition candidates are confirmed.
Evaluation points:
- Color uniformity and vibrancy
- Body-shape perfection
- Fin finishing
- Overall proportions
Fish passing this stage are entered in yearling exhibitions.
Green Water (Greenwater) Use
"Green water" or "greenwater"—water colonized by phytoplankton (primarily chlorella and green algae)—has long been used by goldfish breeders for yearling development.
Benefits of green water:
- Phytoplankton supply sustained vegetative nutrition
- Natural carotenoids promote color enhancement
- Diffused light reduces direct-sunlight stress
- Water buffering (pH stabilization, ammonia absorption)
Making green water:
1. Fill an outdoor plastic tub in a sunny location
2. Add a small amount of existing green water as seed
3. Naturally turns green within 7–10 days
4. If too concentrated (darkening), dilute with partial water changes
Color-Enhancing Feeds
Goldfish feeds containing color-enhancing compounds promote vibrant coloration.
| Ingredient | Effect | Food Sources |
|---|
| Astaxanthin | Enhances red and orange pigmentation | Bloodworm, shrimp, spirulina-containing feeds |
| Carotenoid | Promotes yellow and orange coloration | Dried krill, spirulina |
| Spirulina | Overall color improvement | Spirulina-containing pellets |
Caution: Overdoing color-enhancing feed causes digestive upset and swim-bladder disease. Balance base feed and color-feed at roughly 7:3, offering special feeding 2–3 times weekly.
Stocking Density and Water-Change Management
Yearling growth rate and body-shape development are heavily influenced by stocking density and water-change frequency.
Optimal Stocking Density
| Container | Recommended Maximum (3–8 cm yearlings) |
|---|
| 60L plastic tub | 30–50 (fry stage); 15–20 post-selection |
| 120L plastic tub | 50–80 (fry stage); 25–35 post-selection |
| 1,000L outdoor pond | 200–400 (post-selection 100 or fewer) |
Overcrowding causes competition for nutrition and water-quality decline, resulting in deformed individuals. Regular culling maintains quality.
Water-Change Frequency and Method
Yearlings have faster metabolism than adults and foul water quickly.
- Frequency: Summer: every 2–3 days; spring/autumn: every 3–5 days
- Volume: 1/3 to 1/2 of total water
- Caution: Large water changes cause temperature and pH shock. Pre-warm new water in sunlight before use.
"Conditioning" Exhibition Yearlings
Preparation for autumn exhibitions (typically October–November) begins in August–September.
- Individual management: House exhibition candidates singly or in small groups
- Water management: Switch from green to clear water (observation becomes difficult in green water)
- Feeding adjustment: Reduce feeding to maintain, not alter, body shape
- Daily observation: Monitor for tail deformities and body-shape changes
Summary
Yearling selection and rearing represent generations of goldfish-breeder expertise. From immediately post-hatch through autumn exhibitions, multiple selection rounds combined with green-water and color-feed management form the foundation for developing superior yearlings. When listing yearlings on Br-Choku, including detailed information on selection stage, exhibition-evaluation criteria, and breeding methodology helps buyers properly assess and select their fish.
