Abstract:
The diet of an invasive crayfish, Cherax quadricarinatus (Von Martens 1868), in Lake Kariba, was investigated using stomach
content analysis (SCA) and stable isotope analysis (SIA). The frequency of occurrence of macrophytes and detritus ranged
between 63.6–97.1% and 20–45.5%, respectively, and the index of relative importance ranked these as the two most
important food items across all size classes. Significant differences in the ranking of fish, macroinvertebrates and crayfish
were found between size classes 29–37.9, 38–46.9 and 47–55.9 mm. Stomach content analysis showed 16% of crayfish
stomachs were empty. Feeding intensity differed significantly between size classes and ranged from 3.46 to 5.21. Stable
isotope analysis was done by comparing δ13C, δ15N and C/N ratios in crayfish muscle and potential dietary items in the lake.
Macrophytes were the most dominant food item (57%), followed by macroinvertebrates (20%), then detritus, and finally fish
and crayfish. Stable isotope analysis revealed that all crayfish size classes analysed were in the same trophic level.
Nevertheless, while SCA showed high dietary overlap among all crayfish size classes (>65%), SIA showed that small
crayfish (< 28.9mm) had limited overlap with large crayfish (> 56mm), with the former showing a higher proportion of
macroinvertebrates in their diet. In Lake Kariba, C. quadricarinatus predominantly feeds on macrophytes, macroinvertebrates
and detritus, which may bring about nutrient cycle alterations in the lake. Littoral habitat changes caused by the
feeding characteristics of C. quadricarinatus might also lead to competition with, and eventual displacement of, some native
littoral fishes in this lake
