Shoaling behaviour of the two-spotted goby

Naturally formed shoals of adult Gobiusculus flavescens in a Swedish fjord ranged in size from a few individuals to several hundred fish and were sort ed by body size. Shoal composition was highly dynamic and any particular gr oup was unlikely to remain together for more than a few hours. Shoaling ten dency of juveniles in laboratory experiments was high, and consistent prefe rences were demonstrated for numerically larger shoals. Large test fish pre ferred to associate with shoals composed of large, over shoals composed of small fish, whereas small test fish associated with both size classes equal ly. The ecological importance of shoaling in small shallow water fish is di scussed, and possible mechanisms for the observed patterns are proposed. (C ) 2000 The Fisheries Society of the British Isles.