Intra‐cohort cannibalism among larval stages of perch (Perca fluviatilis)

Cohorts of perch larvae, hatched within 24 h, developed into a bimodal body size distribution as early as 6 days after commencement of external food uptake. At this development stage, intra‐cohort cannibalism occurred among larval perch individuals of larval stage V (body size: 10.5±0.26 mm, 95% c. l.) on smaller siblings. In experimental trials the consumption rate (C: no. of prey/predator·hour) increased exponentially with size of predatory perch (L: mm) and at 21°C was expressed by the relationship log C=3.406·log L‐3.848 (n=10, r2=0.98, P<0.001). For predatory perch in larval stage V, consumption rate was reduced when Daphnia pulex were added, while not in later stages. Perch larvae experimentally forced to live as true piscivores without additional food items developed from stage V to stage IX (15.8±1.34 mm) within the same time as those fed on Daphnia alone, but with increased mortality.