The school behavior of Leucaspius delineatus (Heckel) in relation to ambient space and the presence of a pike (Esox lucius).

1. Tests were carried out to study school concentration in relation to quality of space and presence of a pike. 2. At a water depth of 60 cm (without pike) school concentration is very much lower than at 20 cm, both at 980 lux and at 0.02 lux. 3. At 0.02 lux in the absence of the predator, the shapes of the water space cannot be ascertained to have an influence. 4. At 980 lux (with and without pike) Shape IV has an intense effect on school concentration. 5. In the dark (0.02 lux) the effect of a pike in intensifying school formation is smaller, the larger the quantity of water.