SCHOOLING AFFECTS GROWTH IN THE 3-SPINED STICKLEBACK, GASTEROSTEUS-ACULEATUS

Three-spined stickleback fry (mean length 20 mm, mean weight 14 mg) were reared for 14 days alone and in groups of six in a constant pei capita water volume. The fish originated from two habitats (rock-pools, sea) of different predation pressure. The fry were fed nauplii of Artemia and commercial aquarium fish food ad libitum. Specific growth rates of solitary and schooling fry differed and were also affected by their origin. The specific growth rates of solitary fry from the sea averaged 1.0% day(-1) (length) and 6.0% day(-1) (weight) and those of solitary rock-pool fry 1.1 and 6.7%, respectively. For group-reared fish the corresponding values were 1.2% (length) and 6.6% (weight), and 1.3% (length) and 7.6%(weight). The finding that schooling sticklebacks grow faster than solitary ones implies that grouping enhances fitness in stickleback fry under the conditions of our experiments.