Assessing Some Bio-ecological Metrics Related to the Growth and Diet of Invasive Gambusia Holbrooki in Different Habitats (lotic Vs. Lentic) of an Island Ecosystem (gökçeada, Turkey)

Despite the widespread occurrences of development plasticity in non-native populations, its underlying causes and consequences for species fitness remain unclear. This study aims to assess the potential invasion characteristics of Gambusia holbrooki in different habitats (lotic vs. lentic) of an island ecosystem (Gökçeada, Turkey), by using metrics related to growth and diet. Fish specimens were collected by electrofishing quarterly between September 2019 and July 2020 in Büyük Stream and the shorelines of the Uğurlu Reservoir. The growth metrics of the species were similar in both habitats, showing positive allometry (b > 3) and high condition (K > 2). The vacuity index (VI), showing low values for each habitat (12.7 in lotic vs. 19.3 in lentic), was a mark of high feeding density of the species. Aquatic insects and zooplankton were the main food items in the diet of this invasive fish, and it exhibited generalist feeding habits with specifics depending on the habitats. Because the species fed heavily on Diptera in the lotic habitat and Cladocera in the lentic habitat, niche breadth values were low (0.16–0.22). It was determined that different habitat types did not have an effect on the LWR and condition of G. holbrooki, but changed its feeding strategy. Positive allometric growth and good condition, a comprehensive food range, high levels of feeding density, and high nutritional plasticity can be considered essential parameters in explaining the invasion success of this fish species living in two different habitat types.