The chapter summarizes current knowledge on fish biology in Lake Kinnear. Nineteen native fish species belonging to six families populate the lake. Three of these species are endemic to the lake and four other species are endemic to the Jordan Valley system. Eight alien species are found in the lake. Four of them are breeding in nature, three cannot breed but are regularly stocked, and one is a hitchhiker that cannot breed. The size structure and abundance of fish in the pelagic zone of the lakedisplay explicitseasonal changes associated with fish spawning migrations and winter-spring recruitment of the dominant bleak M. terraesanctae. Water level fluctuations beyond natural have modified the littoral habitats, which are of specific importance during different life stages of fish. Water level has an immense impact on fishreproduction, survival, recruitment, population dynamics, and eventually determines the catches of commercially important species.