Beobachtungen über die entwicklung des schwarmverhaltens bei den larven des herings Clupea harengus

Herring larvae were obtained through artificial spawning of Downsherring caught in the southern North Sea near Ijmuiden (Netherlands) on November 18/19, 1965. The eggs were transported to the Marine Station of the Biologische Anstalt Helgoland and transferred into 140 l tanks (Blaxter and Hempel, 1961) using a closed water circulation (inside filter; Fig. 1). All tanks were placed in a dark room at a constant temperature of 10±0.1 °C. Artificial light was kept at a level of about 1.500 lux at the water surface of the tanks for 12 h per day. Dawn was simulated over a period of 30 min in order to avoid abrupt changes in light conditions. The first observations on schooling behaviour were made about 60 days after hatching: at this time the larvae had reached a total length of about 25 to 30 mm. Grouping began with “contact behaviour” of two single individuals: these swam together in the same direction for a matter of seconds only. Groupings of two individuals occurred simultaneously at different places in the same aquarium. Sometimes the larvae formed greater aggregations involving up to 20 individuals. The distances between the larvae were not constant and varied considerably. Shortly after the formation of a school, the initial groups could be distinguished (Fig. 3). Starved larvae tended more towards schooling than well-fed individuals. If food were offered, schooling behaviour ended abruptly.