Laboratory and in-situ studies on larval development and swimming performance of Pacific herringClupea harengus pallasi

Pacific herringClupea harengus pallasi larvae were caught alive in Departure Bay, B.C., Canada, after being attracted towards light. Growth of larvae was observed during a 5-week period. Larval total length (measured in live anaesthetized specimens) during this period increased from 8 mm to 28 mm. Development of condition factor was observed through the yolk-sac stage until the early post yolk-sac stage. Condition factor decreased linearly in yolk-sac larvae and increased in post yolksac specimens. Swimming performance of Pacific herring larvae in their natural habitat was studied during the day by means of direct observations and compared with laboratory investigations conducted with “wild” and laboratory-reared larvae. In the laboratory (black 35-cm diameter tanks, 10°C) “wild” larvae swam more slowly and were less active (measured as % active time) than in their natural habitat. Laboratory reared larvae showed depressed activity when compared with “wild” larvae observed in the sea. This phenomenon was attributed to deprivation of stimuli in confined containers which might have some bearing on the validity of data gained from controlled ecosystem experiments.