Selection for Surface Feeding in Farmed and Sea-Ranched Masu Salmon Juveniles

Abstract
The feeding behavior of Japanese masu salmon Oncorhynchus masou (also known as cherry salmon) 3–4 months old differed among fish from wild, farmed, and sea-ranched parents. Between feeding intervals, wild-derived fry groups stayed lower in their separate stream tanks than farmed or ranched fry. When slow-sinking food was offered, the wild fry made foraging bouts from the bottom, whereas the domesticated (farmed and sea-ranched) fry stayed close to the surface. Consequently, the domesticated fry finished their meal faster than the wild fish. Over time, all stocks moved up higher in the water column and fed faster, but a difference between wild and domesticated fish persisted. Levels of aggression were similar among the three stocks and observation periods. Sea-ranched fish were intermediate between wild and farmed fish in most recorded behaviors. Staying close to the water surface obviously is a successful strategy under standard salmon husbandry conditions, but an innate tendency to seek the surf...