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

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Abstract
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, PDaphnia 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.