Life history traits of Prussian carp (Carassius gibelio) in Saskatchewan, Canada: Age, growth, and reproduction on an advancing invasion front

Abstract

The Prussian carp (Carassius gibelio) is one of the most invasive fish species in Europe, and it was recently discovered in North America in Western Canada. Our knowledge of basic life history parameters, such as growth rate and mode of reproduction for Prussian carp in their new invasive range, is currently limited. In addition, Prussian carp were only recently discovered in Saskatchewan, but how long have they been in the province, and the stage of invasion is uncertain. Prussian carp can use two modes of reproduction: (1) gonochoristic, involving males and females; and (2) gynogenesis, whereby populations consist of only triploid females that steal sperm from other fish species. Newly introduced populations of Prussian carp tend to be all female and triploid, but their ploidy and mating system in Canada has not been determined. In addition, when and where spawning occurs in newly colonized waterways is completely unknown. Given these important knowledge gaps in fundamental aspects of Prussian carp biology, I focused on describing the life history traits of Prussian carp in Saskatchewan using a mixture of field and lab approaches. I found that Prussian carp in Saskatchewan are slow growing compared to other invasive populations worldwide, and take up to 2x as long to reach sexual maturity. The oldest fish I collected in Saskatchewan was 16 years old in Lake Diefenbaker, and 13 years old in Stockwell Lake, indicating that Prussian carp have been established in the province for many years and were undetected. Similar to well established populations in other parts of the world, Saskatchewan Prussian carp had mixed ploidies with diploid (2n), triploid (3n), and tetraploid (4n) individuals intermixed. In Lake Diefenbaker only female fish were detected, but males were present in Stockwell Lake in low quantities (0.14:1; M:F). Emergence of young of the year Prussian carp in Lake Diefenbaker began in early July and continued through August; however, most spawning in this area likely occurred during mid-June. The timing of spawning and habitat use by juvenile Prussian carp overlaps with that of a variety of native sucker and shiner species. My findings suggest that Prussian carp are well established in Saskatchewan and are likely in the invasive spread phase of invasion. They pose an immediate threat to native biota in Canada locally in Saskatchewan, and via dispersal and colonization of other locations.