Demographics, status, and dietary habits of swordtail fish Xiphophorus helleri Heckel, 1848 in a protected botanical garden and surrounding areas

One of the major challenges faced by protected areas is the introduction and subsequent spread of invasive non-native species, which must be effectively managed to ensure protected area function.In protected freshwaters, fish invasions are a substantial threat through impact mechanisms such as predation and hybridisation.Xiphophorus helleri, a freshwater species native to northern Mexico and Central America, was introduced globally through the aquarium trade and has become established in various non-native habitats.The distribution of swordtail fish Xiphophorus helleri in the Lowveld National Botanical Garden (LNBG) and the nearby Crocodile River system was assessed by investigating its growth, mortality rate, population structure, and diet composition.This study provides new insights, revealing that swordtail fish, which had not been previously recorded in the Crocodile River system, are now present in this area.Sampling conducted in October 2023 and March 2024 revealed significant population of X. helleri in a LNBG pond and in the nearby Crocodile River downstream of the pond, accounting for 91.7% of the total fish caught.We found that X. helleri exhibited rapid growth and competitive superiority, likely contributing to its dominance over native species.Mortality rates were found to be low, suggesting that X. helleri is well-suited to the environmental conditions of the LNBG and Crocodile River systems.This spread indicates that the species' distribution was influenced by local hydrology, particularly the occasional flooding of the pond into the Crocodile River.The findings highlight the threat posed by X. helleri, which can potentially outcompete native species, underscoring the need for effective management strategies to control the spread of X. helleri and mitigate its ecological impacts.