Ecological implications of the absence of parasites on the gills of an isolated fish population

The absence of monogenean parasites in fish is a rare and intriguing occurrence in natural populations, often raising important questions about the environmental and biological factors at play. In this study, we focused on the gill ectoparasites of the Neotropical characid Psalidodon aff. fasciatus, the sole fish species inhabiting an isolated lake, millions of years old, located within a sinkhole in southern Brazil. A sinkhole is a steep, deep depression in the ground that forms a lake disconnected from other bodies of water, creating a unique and highly isolated environment. Over the span of a year, we examined 123 individual fish from this environment and found no ectoparasites on their gills. This striking absence of parasites reveals a complex scenario of evolutionary adaptations, potentially influenced by the isolated nature of the ecosystem. These findings challenge conventional perspectives on species interactions and parasitism, providing new insights into how organisms adapt to specific environmental conditions and prolonged isolation.