Abstract

The fish parasite, Neoergasilus japonicus (Harada, 1930), native to Eastern Siberia and the Amur River catchment area, invaded European water bodies in the middle of the last century, possibly due to the human-mediated distribution of fish in the Amur complex (i.e., the genera Hypophthalmichthys and Ctenopharyngodon). In the deep karst lake, Grand Laoucien (Marseille area, France), this species had an unusually high population density (from 1000 ind./ m3 in zooplankton to 4000 ind./ m3 in the nearshore area) during the free-living period of its life cycle. The annual cycle of N. japonicus includes a 5-month overwintering of fertilized females attached to fish fins and, following this, a five- to six-generation chain from March to November, when the free-living stages in the population alternate with parasite females which attach to their hosts for breeding. The population density of the parasites in zooplankton increased exponentially from spring to autumn, which positively correlated with temperature. We found a strong correlation between N. japonicus density and the community development of microphytobenthos, but not between N. japonicus and phyto- or zooplankton dynamics. The local contributing factors included a seasonal three-fold decrease in water levels and the development of anoxia in profundal waters, which led to a high ambient fish density and thus susceptibility to the parasite. Although the free-living parasite represented only 1% of zooplankton production, it consumed up to 25% of small invertebrate productivity. The maximum intensity of infection reached 140 parasites per fish, or 4.14 per g of weight. The high infection of fish with this parasite, in our opinion, indicated the danger it poses to the local ichthyofauna, which first encountered this new parasite.

Highlights

  • For food relations with other hydrobionts, we examined stomach contents in copepodids 3–5 of N. japonicus from field samples collected during summer–autumn

  • We found that the period of time with a temperature above 10 ◦ C was strongly related to the population dynamics of N. japonicus (Z = −3.818; p < 0.001)

  • The second time we found N. japonicus in zooplankton as copepodids 2–5 and males was on 15 June

Read more

Summary

Introduction

Neoergasilus japonicus, a fish parasitic copepod widely distributed in East Asia, was first described in Taiwan [1]. In the late 1960s, it was found in Slovakia and Hungary [2,3], possibly as a result of the introduction of oriental fish. This was followed by findings of the parasite in France, Great Britain, Cuba, Finland and the USA [4,5,6,7,8,9,10]. The species is actively spreading around the world, finding new hosts and changing the existing population relationships

Objectives
Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call