Managing Aggression When Introducing a Fantail to Common Goldfish

Common Goldfish Are Boisterous

They chase everything—new fish, each other, reflections. A 2" fantail is a target. The nudging is likely spawning behavior (males chasing female) or curiosity.

Risk Assessment

• Fancy goldfish are slow, delicate. Commons are fast, rough.
• Torn fins, scale loss, stress death are real risks.

Decision Framework

• If fantail shows injury or constant hiding: Remove immediately.
• If chasing is mild and fantail eats/vents: Give 1 week. Provide extra cover.
• Best practice: Keep fancies separate from commons.