Uniform maternal age/size and light restrictions mitigate cannibalism in Clarias gariepinus larvae and juveniles reared under production-like controlled conditions

Individual size, size variability, cannibalism, total mortality and biomass production were studied in Clarias gariepinus in two experiments. In the Experiment 1st (duration 7 weeks) larvae originated from three females 1, 2 and 4 years old (females A, B and C, respectively). Three sibling (AA, BB and CC) and three mixed (AB, AC and BC, 1:1) larval groups were reared at a 12L:12D, 50 lux light regime. Initial individual weight of larvae in the sibling groups was strongly positively related to female age, this was preserved during 7 weeks of rearing. Initial coefficient of variation for weight was moderate in the sibling groups from young females AA and BB (30–33%), whereas it was elevated in the mixed groups (48–79%), especially in the group AC. Cannibalism was the major component of total mortality. Cannibalism in progeny of young females AA, AB and BB was reduced compared to the groups BC, AC and CC. Final biomass of small larvae issued from young females was higher than the final biomass of large progeny of the oldest female because of reduced cannibalism in the former. In a 6 week Experiment 2nd progeny of one female was reared at three light regimes: L (continuous light, 400 lux), N (“normal” 12L:12D, 50 lux) and D (continuous darkness). The final individual weight of fish was the lowest in the L group, highest in the D group, and intermediate in the N group. Final coefficient of variation for weight, cannibalism and total mortality were significantly reduced by light restrictions. The resulting final biomass was the lowest in the L group, intermediate in the N group and the highest in the D group in which it was higher by a factor 3.8 compared to the L group. Based on the results of present work and on literature overview several pathways were identified along which biomass size may be modified in populations of young fish that exhibit cannibalistic propensity. Selection of young female spawners of uniform age, and light restrictions, are recommended to mitigate cannibalism.

► Two techniques to mitigate cannibalism in young C. gariepinus were recommended.
► Progenies from C. gariepinus females of uniform age/size need to be used.
► Another promising technique is light restrictions.
► We identified pathways along which biomass size is modified in young cannibalistic fish.