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

SIMPLE SUMMARY: Bigheaded carps (bighead carp and silver carp) originated in Southeast and East Asia, and their hybrids were stocked for economic reasons to Hungarian natural waters such as Lake Balaton for decades, while the Tisza River was populated by escaped individuals with farm origins. The presence of these alien species and their hybrids in Hungarian natural water bodies may pose significant ecological risks (connected with their phytoplankton and zooplankton consumption). To be able to deal with the ecological risks and to understand the potential of invasiveness of these species, one must have information on the population-level genetic structures of these alien fish stocks. Ten microsatellite DNA markers and one mitochondrial marker were used to address these questions. The results showed that the two stocks are genetically different; the lake population was genetically more diverse and consisted of hybrid and silver carp individuals, while the river population contained only silver carps. The mitochondrial sequences found in the two populations originated from the Yangtze River. Based on the different genetic structures of the stocks, one can assume that bigheaded carps do not reproduce in Lake Balaton, while the Tisza River stock represents significant reproductive potential and may become invasive in this river. ABSTRACT: Bigheaded carps (bighead carp, Hypophthalmichthys molitrix, and silver carp, Hypophthalmichthys nobilis) and their hybrids play an important ecological and economic role in their original habitat, while their introduced stocks may pose serious ecological risks. To address questions about the persistence and invasiveness of these fish, we need to better understand their population structures. The genetic structures of bigheaded carp populations inhabiting Lake Balaton and the Tisza River were examined with ten microsatellite markers and a mitochondrial DNA marker (COI). The Lake Balaton stock showed higher genetic diversity compared with the Tisza River stock. Based on hierarchical clustering, the Tisza population was characterized only by only silver carps, while the Balaton stock included hybrid and silver carp individuals. All COI haplotypes originated from the Yangtze River. Based on the high genomic and mitochondrial diversity, along with the significant deviation from H–W equilibrium and the lack of evidence of bottleneck effect, it can be assumed that bigheaded carps do not reproduce in Lake Balaton. The present stock in Balaton may have originated from repeated introductions and escapes from the surrounding fishponds. The Tisza stock consists solely of silver carp individuals. This stock appears to have significant reproductive potential and may become invasive if environmental factors change due to climate change

Correlation between Heavy Metal-Induced Histopathological Changes and Trophic Interactions between Different Fish Species

This study assessed the distribution of heavy metals in the gills, kidney, and liver, correlated with the severity of histopathological changes, of three fish species with different feeding habitats (Barbus barbus, Squalius cephalus, and Chondrostoma nasus) from the Crisul Negru river, Romania. The levels of copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb), and zinc (Zn) in fish tissues were measured by atomic absorption spectrophotometry. Histopathology and the expressions of TNF-alpha and proliferation cell nuclear antigen (PCNA) were investigated by immunohistochemistry and Western blot. Our data suggest a significant correlation between the bioconcentration level of metals and structural changes. The carnivorous species was the most affected compared to the omnivorous and herbivorous ones, and the most affected organ was the kidney. Moreover, the correlation of tissue damage with the PCNA and TNF-alpha expression levels revealed that the herbivorous species presented less extended lesions, likely due to higher activated repair mechanisms and lower levels of inflammation. In conclusion, our data and the subsequent statistical analysis suggest that feeding behavior could be correlated with the histopathological alterations and might be used for a more profound evaluation of aquatic environment safety and analysis of aquatic ecosystems

Potential reproduction of invasive Asian carps (Hypophthalmichthys spp.) in Lake Balaton: pro and contra evidences

Asian carps (bighead carp Hypophthalmichthys nobilis × silver carp H. molitrix) had been introduced into Lake Balaton (Hungary) from 1972 to increase fishery yields and as a biological control of algal blooms. Although the stocking was stopped by 1983, the biomass of Asian carps is still high in the lake, constituting about one-third of the total fish biomass. Our analyses revealed that the present Asian carp stock cannot have originated directly from the last official stockings. The origin of the present stock is undefined, and there are two potential explanations for the source of recruitment. First, it is possible that Asian carps escape from the nearby fishery ponds and get into Lake Balaton periodically. The second explanation is that Asian carps spawn in the lake. However, preceding studies suggested that Asian carps are not able to reproduce in lacustrine environments. In this study, our aim was to contrast the pro and contra evidences of natural Asian carp reproduction in Lake Balaton. We studied the reproductive parameters and genetic pools of 58 Asian carps, sampled between March−November 2011 and 2013. Mature vitellogenic oocytes and post-ovulatory follicles were found in the posterior segments of gonads. This suggests that a fraction of mature eggs was released from the ovaries during the year, but does not necessary imply successful reproduction. Considerable seasonal variations in gonado-somatic indexes (GSI) were observed, fluctuating between 6−28% in 2011 and 12−29% in 2013. However, the within-year dynamics of GSI changes suggest that fish do not release significant amounts of milt during the potential spawning period. Rather, the resorption of nutrients allocated to eggs seems probable during autumn. Genetic analyses showed remarkable deviation from Hardy-Weinberg equilibrium within the stock, which indicates that Asian carps do not constitute a closed, self-sustaining population in Lake Balaton

Ecological impacts of filter-feeding Asian carps (Hypophthalmichthys spp.) in Lake Balaton, Hungary

Bighead carp (Hypophthalmichthys nobilis), silver carp (H. molitrix) and their hybrids (collectively referred as Asian carps−AC) are primarily planktivorous cyprinid fishes that have been introduced into more than 30 countries around the world, including Hungary. However, recent studies demonstrated that AC can adversely affect the water quality and native fish populations. In this study, we report on the rate of hybridization, growth parameters and feeding habits of AC, to assess their ecological impacts and life history traits in the oligo-mesotrophic Lake Balaton. We found that the majority of the investigated AC (n=116) were hybrids. In general, hybrid AC with silver carp characteristics dominated the stock (90%), but 10% of individuals exhibited bighead carp phenotype and the proportion of bighead carp genes exceeded 98% in 4 individuals. However, the variance in phenotypes and the rate of hybridization did not influence significantly the feeding habits. Rather, the food composition was determined by the availability of different food resources and the concentration of suspended inorganic particles in the ambient water. Stable isotope analyses and microscopic analyses of gut contents revealed that the vast majority (>99%) of the ingested and metabolised food was zooplankton (mainly Rotifers, Cladocerans and Copepods). Despite the low proportions of algae in the food, we identified 155 phytoplankton taxa in the foregut-contents, among which there were several species (e.g., Scenedesmus spp. and Microcystis spp.) that survived the passage through the guts. Growth rates of AC were intermediate in Lake Balaton, while their condition factors were relatively high compared with other ecosystems. The relatively high condition factors were particularly interesting in the light of the high inorganic matter content of ingested food (43±9% in dry mass). We conclude that the presence of AC is an ecological threat to Lake Balaton, because AC can be important resource competitors of native planktivores

The impact of trace metals on wild fish living in Crisul-Negru river from North-Western Romania: bioaccumulation and histopathological biomarkers

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