Test tanks for measuring anti-predator behavior (100 × 30 × 40 cm; A) and for survival rate with exposure to a predator (B). The former containing (a) predator mandarin fish; (b) a transparent partition; (c) a compartment containing 5 wild or hatchery-reared C. idellus selected at random; (d) gravel shelter; (e) light source, and (f) fixed tube used to introduce a predator. The tank was divided into a risky area (g) and a non-risky area (h). The latter containing (a) test tank (φ, 150 cm; H, 100 cm); (b) two predator mandarin fish; (c) 10 wild and 10 hatchery-reared C. idellus selected at random (size-matched); (d) aquatic plant shelter; (e) gravel shelter; and (f) light source.