Reproductive plasticity and environmental tolerance of invasive African catfish (Clarias gariepinus) in a tropical Brazilian river.

Invasive alien species (IAS) pose a significant threat to biodiversity, particularly when endowed with high ecological and reproductive plasticity. The African catfish, Clarias gariepinus, is one such species, widely recognized for its ability to colonize and establish in diverse tropical ecosystems. This study evaluated the reproductive success of C. gariepinus in a tropical environment by examining gonadal maturation stages, reproductive indices and water physicochemical variables associated with reproduction. The analysis revealed a population predominantly composed of adult individuals at various reproductive stages, with a higher concentration upstream during the dry season. The species exhibited continuous reproduction throughout the year, irrespective of body size, demonstrating both high fecundity and notable environmental flexibility. Dobriyal's Reproductivity Index (DI) proved effective in identifying gonadal maturation patterns independently of somatic size and is particularly useful under conditions of limited sampling. Statistical analyses revealed a strong association between DI and key physicochemical parameters (i.e., particularly elevated dissolved oxygen concentrations and pH values within optimal ranges) which collectively influence species distribution and reproductive success. These findings underscore reproductive plasticity and environmental tolerance as pivotal strategies underpinning the invasive potential of African catfish in tropical systems. We conclude that ongoing monitoring and targeted management interventions are crucial for mitigating the ecological impacts of C. gariepinus and alleviating pressure on native fish communities.