Population traits and colonization success of non-native Eurasian perch ( Perca fluviatilis ) 35 years after its first appearance in the Mediterranean Lake Skadar

Abundance, spatial distribution, population structure and growth of non-native Eurasian perch ( Perca fluviatilis ) were examined in the Lake Skadar, a large, unstratified lake in the Mediterranean region inhabited by several endemic, rare and threatened fish species. Fish were caught in the infra-littoral and littoral habitats of the northern and central parts of the lake using multi-mesh gill nets over three consecutive years. Eurasian perch was among the most dominant species in both habitats. The mean relative abundance is - NPUE (0.556 individuals m −2 ) and relative biomass is - WPUE (23.56 g m −2 ) (years and habitats combined). Its population consisted primarily of individuals in first, second and third year of life span (0+ − 2+ age classes). The youngest fish in first and second year showed low mortality rates, older fish in third, fourth, fifth and sixth year of life span (age classes 2+ − 5+) experienced great losses, with mortality rates ranging from 0.6–1.0. The von Bertalanffy growth curve formula, expressing the expected total length L t = 36.98 (1-e -0.23 (t + 1.018) ) with growth performance value Φ ’ = 2.50, revealed fast growth-in-length. Length-to-weight relationship was W t = 6.2 × 10 −3 L t 3.27 , indicating positive growth-in-weight. It has been concluded that 35 years after the first finding in the Lake Skadar, Eurasian perch adapted well to local conditions in this Mediterranean environment, with the life span changed in favor of fast growth and early maturation.