Lack of host specialization despite selective host use in brood parasitic cuckoo catfish

Sampling was conducted by SCUBA diving and snorkelling. During each dive, we set a benthic screen net (20 m long and 1.5 m high, mesh size 10 mm) along the bottom at a particular depth and searched for mouthbrooding cichlid fish in close vicinity. Mouthbrooding fish are easily recognized by their extended buccal cavity. Immediately after each dive, the collected females were identified to species level, their body length was measured to the nearest mm, and the broods were collected by gently washing them out of the maternal buccal cavity using the water jet of a Pasteur pipette. The offspring of each brood was photographed, counted, and the age was estimated based on offspring developmental stage. Parasitic eggs and embryos were clearly visible during brood inspections (smaller size, characteristic colour and shape). When parasitic offspring were detected, they were counted, measured to the nearest 1 mm, euthanised and stored in 96% ethanol. For each brood, we recorded host species, host size, depth of host collection, host brood size, developmental stage of the brood, occurrence of parasitism and, when the brood was parasitized, the number and size of parasitic offspring. Host brood developmental stage was estimated visually based on embryo and yolk sac size. We considered this estimate reliable until the age of 3 weeks. To mitigate uncertainty around our brood age estimates, we then converted brood age into a new variable, termed brood stage. Brood stage comprised five categories; eggs (age 1-5 days), early embryo (6-10 days old), mid embryo (11-15 days old), late embryo (16-20 days old), and juvenile (21 days and older).