Using the Kariba Invitation Tiger Fishing Tournament for monitoring an invasive crayfish Cherax quadricarinatus in Lake Kariba, Zimbabwe

The stomach contents of tigerfish Hydrocynus vittatus, caught in an angling competition on Lake Kariba, were examined to determine the extent to which they feed on the invasive crayfish Cherax quadricarinatus. The stomach contents of 281 tigerfish caught during three tournaments (2013, 2014 and 2015) were examined and grouped into six main categories. The proportion of empty stomachs ranged from 4.6 to 13.9% in males and from 11.9 to 29.1% in females. The main food items according to the frequency of occurrence were fish (Limnothrissa miodon (69.0 ± 13.0%) fish remains (bones and scales; 33.0 ± 22.0%), Cichlidae (26.8 ± 2.10%) and Mormyridae (0.5 ± 0.9%) and invertebrates, such as crayfish (24.9 ± 4.6%) and insects (5.2 ± 2.1%). This tournament has been useful in confirming changes in tigerfish diet following the introduction and establishment of non-native species, such as Limnothrissa miodon and, more recently, the crayfish, C. quadricarinatus.