Parasitism is one of the most successful evolutionary strategies, yet it remains poorly studied in marine apex predators such as sharks. Understanding shark–parasite interactions is critical for improving our knowledge of host health, ecosystem condition and the evolutionary relationships between hosts and parasites. Bull sharks (Carcharhinus leucas) are euryhaline elasmobranchs, utilising freshwater and estuarine habitats throughout tropical and subtropical regions globally. Despite photographic and anecdotal evidence of external parasites on bull sharks, few studies have investigated parasite species, parasite load, or potential health impacts in wild populations. Bull sharks are frequently encountered in the river systems of southeast Queensland, Australia, providing a unique opportunity to investigate parasite ecology in free-ranging hosts. Microbothriid monogeneans, a highly specialised group of parasitic flatworms, were collected from wild bull sharks in the Pumicestone Passage, Maroochy River and Noosa River and have been identified as Dermophthirius maccallumi using morphological examination and DNA sequencing. To date, only a single formal record for D. maccallumi from bull sharks exists in Australia, highlighting the need for further detailed ecological, morphological and molecular investigations of Dermophthirius in Australian waters. Parasite abundance will be examined in relation to host traits and environmental variables. This research will provide new insights into the ecology of D. maccallumi in wild bull sharks, while evaluating its potential as an indicator of estuarine conditions and host health, thereby contributing to conservation planning in UNESCO Biosphere Reserves, improving our understanding of host–parasite ecology in a vulnerable apex predator.