When selecting good koi fish, you need to consider the following aspects:
Body Shape: High - quality koi should have a well - proportioned and robust body. The fish's back should be straight, maintaining a left - right balance. When swimming, it should move steadily and upright. The head should have a good shape, with a wide distance between the eyes, a large gap between the eyes and the mouth, and a thick snout. The pectoral fins should be evenly sized and rounded, and the caudal peduncle should be thick and powerful.
Body Color: The body color of koi should be rich, bright, and naturally pigmented. The colors should be pure and intense, without any variegated colors or being too pale. Healthy koi have bright body colors. White koi should be pure white, and red - colored koi should be bright red.
Patterns: The patterns should be clear, neat, evenly distributed, and distinctive. There should be a break in the patterns on the shoulder (called "shoulder break"). The patterns on the caudal peduncle should have a finishing color spot, and the patterns should extend towards the abdomen. The overall patterns should conform to the characteristics of the variety.
Health Condition: Healthy koi swim nimbly, are responsive to their surroundings, and are active eaters. Their body surface is smooth, and their fins and scales are intact without any abnormal swimming behaviors. Avoid choosing koi with obvious diseases, such as white spot disease or fungal diseases.
Swimming Posture: Good koi maintain body balance while swimming. Their pectoral fins are strong, the caudal peduncle swings moderately, and their movements are coordinated and aesthetically pleasing.