VISUAL CHARACTERISTICS OF MANDARIN FISH(SINIPERCA CHUATSI)IN RELATION TO ITS FEEDING HABIT III.VISUAL RESPONSE TO PREY MOTION AND SHAPE

Feeding beliaviour was recorded to study the visual response of an ambushingpiscivore,the mandarin fish,Siniperca chuatsi,to motion and shape properties of various preys. Amomg several live organisms tested,the live prey fish were most frequentlystalked and attacked.Live slirimps were less frequently stalkedand scarcely attackedand live dragonfly nymphs least frequently stalked and never attacked.No visualresponse of the mandarin fish has been observed to dead organisms.For the moving dead prey fish driven by an experimental device,the mandarinfish stalked and attacked most frequently the intermittently fast-moving(v≥10cm/s)prey fish,staiked and attacked less frequently the intermittently or continuouslyslow-moving(v≤5cm/s)prey fish,and stalked most frequently but scarcely ornever attacked the fast continuously moving prey fish.For the intermittently slow-moving(v=5cm/s)artificial preys of 6 kinds ofshapes(a,6,c,d,e and f),the mandarin fish stalked all of tliem at the rates of 0.50,0.24,0.25,0.25,0.70,and 0.90 times per minute per mandarin fish respectively.But mandarin fish only attacked the artificial preys of a kinds of shapes(3,e and f)and the attacking rates were 0.18,0.45 and 0.67 times per minute per mandarin fishrespectively.The eye of the mandarin fish can perceive the motion of preys within certaindistance,which determines the relatively long-ranged stalking behaviour of the fish.But its eye can perceive approximate shape of preys only within a rather closerange,which determines the short ranged stalking and attacking behaviour of this fish.