# Mixed Doitsu Koi The Doitsu Koi represents centuries of selective breeding in Japanese ponds, a domesticated carp engineered for both aesthetics and personality. Unlike their fully-scaled cousins, Doitsu varieties display partial or mirror scaling?large individual plates running along the lateral line and dorsal surface?creating a texture as distinctive as their coloration. These fish are remarkably expressive, developing individual swimming patterns and recognizing their keepers over time. They'll hover near the surface during feeding, their mouths breaking the water with eager confidence, and many develop enough personality to seem almost interactive. Thriving in Doitsu Koi requires understanding that these aren't confined-space fish despite their common aquarium availability. A 100-gallon minimum applies to juveniles; these fish grow steadily toward three feet and demand robust filtration to handle the biological load they generate. They produce substantial waste, so weekly water changes of 20-30% and a high-quality external filter aren't optional?they're foundational. Koi also interact directly with substrate and plants, rooting through gravel and uprooting vegetation with casual enthusiasm, so expect a somewhat sparse planted environment or plan for sturdy, anchored specimens they can't displace. Tank mates matter more with Koi than size suggests. While not aggressive, they're indiscriminate foragers and will consume anything small enough to fit in their mouths, making them incompatible with most community fish beyond similarly-sized carp species. Their peaceful nature shines brightest in species-specific or koi-only setups where they can establish a loose hierarchy and exhibit natural schooling behaviors. With proper care and stable conditions, these fish often outlive the aquariums they inhabit?40-year lifespans aren't exaggeration but documented reality in well-maintained systems.