Source of bigheaded carp (Hypophthalmichthysspp.) in Lake Balaton, Hungary: natural recruitment or continuous escapement from aquaculture?

Abstract

The worldwide spread of bigheaded carp (Hypophthalmichthys spp.) is considered an ecological threat and problem in many countries. The aim of this study was to consider the likelihood of bigheaded carp reproduction in Lake Balaton and its catchment area (Hungary).The within-year trends of gonadosomatic index values show that female bigheaded carp increase ovary masses from spring until midsummer, after which a decline is typical. This trend may indicate bulk egg release, but the lack of a sharp drop in fecundity (number of eggs 2 in the ovary) values during and after the potential spawning period suggests that a general and considerable ovary evacuation does not likely explain the declining gonadosomatic index values. Rather, it is more probable that female bigheaded carp resorb their eggs, supported by the presence of atretic oocytes in the ovaries after the potential spawning season. In turn, postovulatory follicles were present in the posterior ovary segments of 2 individuals, indicating that mature eggs were released by some females. The evidence of sporadic egg release does not necessarily imply that successful reproduction has occurred, however. The genetic analyses showed remarkable deviation from Hardy-Weinberg equilibrium within the stock, suggesting that bigheaded carp do not constitute a natural reproductive community in Lake Balaton. Thus, the present bigheaded carp stock in Lake Balaton likely derives primarily from external origin (i.e., from the surrounding fish ponds).

Alien fish, amphibian and reptile species in Romania and their invasive status: a review with new data

“…Some studies claim that H. molitrix can compete with native planktivorous species, e.g. in lake Balaton (Boros et al 2015), where, however, the stock is derived from farming, not reproducing in free waters (Vitál et al 2017). Other authors estimate that its impact upon native species is limited, as it has reached an ecological equilibrium state (Lenhardt et al 2011) or is insufficiently known (Soes et al 2011;Povž 2017), as is its capacity of controlling algal blooms (Vörös 2000;Oțel 2007).…”

Effect of non-native species on taxonomic and functional diversity of fish communities in different river types

“…This statement is well-supported by our data, since many non-native species separated from natives in several morpho-functional traits. For example, the Ponto-Caspian gobies, which are already among the most common species in Danubian rip-rap habitats (Copp et al 2005;Erős 2005;Brandner (Takács et al 2017;Vitál et al 2017). Moreover, gobies and carp species are functionally different community members, indicated by their opposite orientation in the multidimensional trait space (shown on the PC1 axis), primarily due to their specific locomotion types and food acquisition characteristics (Fig.…”

Comparison of the Genetic Structure of Invasive Bigheaded Carp (Hypophthalmichthys spp.) Populations in Central-European Lacustrine and Riverine Habitats

“…The sampling locations are shown in Figure 1. In the case of Lake Balaton, we used 108 fin samples collected in the study [19] between 2011 and 2013 describing the species hybrid's reproductive status for further analysis, supplemented with an additional eight samples collected from the inflow areas of the lake. A further 31 samples were collected from the Tisza River (at the Tisza-tó section) in 2014.…”

“…There are reports on spawning observations of the two species in the Romanian and Serbian sections of the Danube and the Tisza Rivers [16][17][18]. In Lake Balaton, the spawning could occur occasionally, but the hatching and survival of the fry are not confirmed [19].…”

“…In contrast to the American and Asian stocks, microsatellite data on the European populations are missing. Only basic genetic information on the Balaton stock (observed and expected heterozygosity from 10 loci) has been published [19].…”