Cannibalism in Larval Fish

Cannibalism in larval and early juvenile fish is size-structured predation in which larger individuals ingest smaller siblings, and it can erase a large share of a cohort within days. It is documented across many farmed species including seabass, seabream, perch, pike-perch, Asian seabass, and grouper. It is driven primarily by size heterogeneity: once the size ratio between the largest and smallest fish exceeds roughly 2:1 in length, gape-limited cannibalism accelerates sharply. Causes include uneven hatching times, temperature or feeding gradients within a tank, and competitive hierarchies that amplify early small differences. Management focuses on compressing size distribution: frequent grading into narrow size classes (every 7-10 days in susceptible species), continuous or near-continuous feeding to keep smaller fish growing and satiated, high feed particle availability at dusk when attacks peak, adequate light so prey fish can see and escape, and tank designs without dead corners where victims are trapped. Removing oversized individuals is more effective than culling runts. Beyond direct mortality, cannibalism damages fins and skin of survivors, opens routes for infection, and wastes feed biomass already invested; in intensively reared pike-perch and grouper, uncontrolled cannibalism routinely exceeds 50 percent losses without grading.