Grass carp (Ctenopharyngodon idella) translocations, including hitchhiker introductions, alter zooplankton communities in receiving ponds

Abstract

In the present study we tested the effects of translocations from aquaculture facilities of grass carp, one of the most commonly used species in aquaculture globally, to constructed ponds in the Auckland region, New Zealand. Primarily, we were interested in whether zooplankton assemblages in recipient ponds are affected by the concomitant introduction of ‘hitchhikers’ with fish releases. Zooplankton community composition was quantified in 34 ponds that had been subject to grass carp release and 31 that had no grass carp introductions. A significant difference in zooplankton community composition was observed between ponds that had received grass carp translocations and those that had not. Differences in community composition between ponds with and without carp releases could be attributed to both the: (1) effects of activity of grass carp through habitat modification; and (2) establishment of hitchhiking zooplankton species originating from aquaculture ponds, including non-native species. Effective measures to curb the proliferation of non-native taxa within aquaculture facilities, and to mitigate the accidental movement of non-native taxa with translocations from these facilities, are required to reduce future zooplankton introductions.