Attila Mozsár - Academia.edu (original) (raw)

Papers by Attila Mozsár

Stoichiometry theory states that individual animal species maintain relatively constant body nutr... more Stoichiometry theory states that individual animal species maintain relatively constant body nutrient contents per unit body mass. However, some recent studies have pointed out that nutrient content can vary significantly within a single species. In this study, we measured the phosphorus-and lipid content, and the condition factor of three fish species (Amur sleeper, pumpkinseed, rudd), assessing the seasonal changes in body nutrient stoichiometry. We found that the phosphorus content of fish changed seasonally within a population. However, the interspecific differences proved to be more significant in phosphorus content. We presume that only a considerable change in lipid content is able to affect the elemental ratios (i.e., the proportion of phosphorus) in fish body, via altering the carbon to phosphorus ratios in general. Significant relationship between condition factor and lipid content was not typical of all species. Thus we assume that the elevated condition factor may not be related generally to fat accumulation, but to increment in other tissue types such as muscle. Kivonat A sztöchiometriai elmélet szerint az élőlények elemi összetétele és a testben raktározott tápanyagok egymáshoz viszonyított aránya fajra jellemző, állandó érték. Újabb vizsgálatok azonban bebizonyították, hogy egy fajon belül is lehetnek szignifikáns különbségek tápanyagtartalom tekintetében. Munkánk során három halfaj (amurgéb, naphal, vörösszárnyú keszeg) foszfortartalmát, lipidtartalmát és kondíciófaktorát mértük, továbbá vizsgáltuk ezek szezonális változását a populációkon belül. A test foszfortartalmának szezonális változását megvizsgálva elmondható, hogy egy populáción belül is előfordulnak szignifikáns különbségek. Hozzá kell tennünk azonban, hogy a fajok közötti különbségek sokkal számottevőbbek. Feltételezésünk szerint a lipidtartalom mennyiségének csak jelentős változása révén képes a test foszfortartalmát megváltoztatni a szén-foszfor arány befolyásolásán keresztül. A lipidtartalom és a kondíciófaktor közötti szoros kapcsolat nem minden populáció esetében figyelhető meg. Előfordulhat, hogy a kondíciófaktor emelkedését nem a lipidtartalom növekedése, hanem más szövetek gyarapodása okozza.

Hydrobiologia, Feb 27, 2017

Influence of environmental factors and individual traits on the diet of non-native hybrid bighead... more Influence of environmental factors and individual traits on the diet of non-native hybrid bigheaded carp (Hypophthalmichthys molitrix × H. nobilis) in Lake Balaton, Hungary.-Hydrobiologia, 794 (1) pp. 317-332.

Aquatic Ecology, Jul 21, 2012

Stoichiometry theory states that the elemental composition of individual organisms is a taxondepe... more Stoichiometry theory states that the elemental composition of individual organisms is a taxondependent trait, and that organisms maintain relatively constant body nutrient composition, independent of food nutrient content or ingestion rate. Some recent studies have pointed out that assuming a strict homeostasis in fish is an oversimplification , so that nutrient ratios in fish bodies may not be as constant as previously thought. In this study, our aims were (a) to assess the overall nutrient composition of roach, (b) to reveal any significant differences in elemental composition of roach between populations from different lakes and (c) to relate these potential differences to environmental parameters and fish condition. The mean elemental composition of roach (whole fish) was 45.0 ± 5.3 % carbon (C), 10.2 ± 0.8 % nitrogen (N), and 2.4 ± 0.5 % phosphorus (P), while their molar C/N/P ratio was approximately 50:10:1. The elemental composition of roach was not as constant as homeostatic stoichiometry models would predict. Significant differences were found in the carbon, nitrogen, and phosphorus contents of fish sampled from different lakes. Productivity of lakes (expressed as chlorophyll-a) was positively correlated with %C, C/N, C/P, and N/P ratios, and negatively correlated with %N and %P. In turn, mean lake temperature was negatively correlated with %C and C/N ratio, but not with other nutrients or nutrient ratios. Condition factor was negatively related to the %C of fish, but it did not correlate significantly with %N, %P, or nutrient ratios. Our results on intraspecific nutrient variation illustrate the potential differences between populations and emphasize the importance of lake-specific approaches. Keywords Roach Á Stoichiometry Á Carbon Á Nitrogen Á Phosphorus This paper is dedicated to the memory of István Tátrai, a great researcher and friend, who passed away before publication.

Journal of Applied Ichthyology, Oct 7, 2013

Hydrobiologia, May 6, 2015

The gut contents of filter-feeding fish often contain considerable amounts of viable phytoplankto... more The gut contents of filter-feeding fish often contain considerable amounts of viable phytoplankton cells, thus these animals can act as vectors and may play an important role in the horizontal and vertical transport of algae. In this study, the potential role of the introduced filter-feeding Asian carps (hybrids of silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis) in algal dispersion was studied in the oligo-mesotrophic Lake Balaton (Hungary). We examined the algal composition in the lake water, gut-contents (foregut and hindgut) and occasionally in the filtered suspensions collected directly from the gill rakers (filtering apparatus) of fish. Microscopic analyses revealed that the phytoplankton composition of the ingested food differed considerably from what we found in the lake water. Cryptophytes, dinoflagellates and euglenophytes were observed in both the lake water and foregut samples, but were absent in the hindgut samples. However, in the cultured hindgut samples we found viable cells of several phytoplankton taxa (e.g., diatoms, blue-greens, desmids, volvocalean and chlorococcalean green algae), which managed to survive the physical and chemical digestion. Thus, it can be concluded that Asian carps can be potential vectors of phytoplankton and facilitate their dispersal. These results imply that the presence of these filter-feeding fish can alter the phytoplankton species composition and promote the dominance of taxa that are able to resist digestion.

Hydrobiologia, Sep 13, 2016

Environmental heterogeneity plays a determinant role in structuring taxonomic and functional comp... more Environmental heterogeneity plays a determinant role in structuring taxonomic and functional composition of local assemblages via various interacting processes as synthetized in the metacommunity theory. In this study we evaluate the relative roles of local environmental and landscape filters, spatial constraints and seasonality in organisation of assemblages of Chironomidae (Diptera), a diverse aquatic insect group with winged adults, in an extremely heterogeneous wetland system, Kis-Balaton, Hungary. As expected, local environmental variables explained a substantial proportion of assemblage variance mainly along sediment structure, macrophyte coverage, and decomposing plant matter gradients. Considering the narrow spatial range of the study area, pure spatial influence was unexpectedly strong, likely because of the dispersal limitation related to tall terrestrial vegetation patches and mass effect related to the uneven distribution and area of certain microhabitats and their species pools. Whereas landscape-and season-related variability proved to be low or negligible. Taxonomic and functional feeding guild (FFG) based approaches revealed the same main trends in assemblage data; however, FFGs seemed to track environmental changes more tightly. We argue for the common use of taxonomic and functional based approaches, and advise the improvement of species optima and tolerance spectra databases to expand bioassessment power.

International Review of Hydrobiology, Jun 30, 2015

In the last two decades, the invasion of the Amur sleeper (Perccottus glenii Dybowski, 1877) orig... more In the last two decades, the invasion of the Amur sleeper (Perccottus glenii Dybowski, 1877) originating from the Far East can be observed in Eastern and Central Europe. Since the Amur sleeper is a non-game fish species, few detailed studies exist on its feeding ecology both in its native and invaded habitats. We examined the seasonal feeding ecology of Amur sleeper in a lentic and in a lotic habitat. Chironomid larvae, zygpoteran larvae, crustaceans and ephemeropteran larvae dominated the diet. No clear differences between the two habitats were found. The diet composition was mainly regulated by the body size that had stronger effect than the habitat and the season. Although fish consumption was uncommon, we anticipate this finding to the structure of the examined populations, in which large bodied individuals were rare. Our study shows that the Amur sleeper may influence several levels (compartments) of the aquatic food web, although the species proved to be an especially important predator of the invertebrate assemblage.

Ecosystem health and sustainability, Dec 31, 2022

ABSTRACT Various types of ground baits are loaded to lakes by anglers, but the ecological role of... more ABSTRACT Various types of ground baits are loaded to lakes by anglers, but the ecological role of these materials is often overlooked. Thus, the aims of this study were to conduct a quantitative and qualitative assessment of the baits used by anglers in the largest lake of Central-Europe (Lake Balaton, Hungary), estimate the annual nutrient balance of recreational fishing, and relate the nutrient loading from this source to the total external load. Our study demonstrated that popular angler baits varied substantially in their nutrient contents and in their molar nitrogen to phosphorus (N:P) ratios. The net nutrient balance of recreational fishing was +19.3 t total N year −1 and +5.2 t total P year −1 , equivalent to 0.7% and 3.2% of the estimated total annual N and P loads, respectively. The rate of nutrient loading may be doubled if the present trends continue: anglers will use 20% more bait with an even higher nutrient content and will also show higher propensity to release the fish after catching. In turn, sustainable nutrient balance of fisheries management could be achieved by limiting the anglers’ bait use to 1.5 kg day −1 and restricting baits to those which have relatively low P (<0.3%) and N (<1.5%) contents.

Hydrobiologia, Apr 26, 2015

The reliable determination of the total phosphorus (P) content stored in aquatic biota is essenti... more The reliable determination of the total phosphorus (P) content stored in aquatic biota is essential for studies on nutrient stoichiometry, as well as for effective lake management measures. However, a variety of methods are found in the literature for sample P content determination, which renders it necessary to assess whether the data reported in different studies are comparable. We used different combinations of combustion durations, acid types and acid concentrations for sample digestion, and measured P concentrations subsequently with the standard colorimetric method. In addition, P contents of samples were assayed by ICP-OES and MP-AES methods. Our results confirmed that the variability among studies using different methods may explain some of the reported intraspecific and interspecific 2 variation. We found that duration of combustion exerted the most important influence on the P retrieval, while acid type and acidity of the hydrolysing solution did not substantially influence the efficiency of sample digestion. We recommend using 8 h of combustion and 0.3 N HCl for acid hydrolysis prior to the colorimetric P analysis, and urge standardisation in the P analyses of biotic samples so as to obtain reliable results and data comparable among different studies.

Frontiers in Marine Science, 2015

Freshwater Biology, Nov 14, 2018

1. Changes in organismal stoichiometry (OS) may be driven by seasonal changes in lipid reserves (... more 1. Changes in organismal stoichiometry (OS) may be driven by seasonal changes in lipid reserves (i.e. energy) and gonadal development in fish. However, these rela

NeoBiota

Biotic interactions exerted by invasive species have a strong effect on ecosystems. Intraguild pr... more Biotic interactions exerted by invasive species have a strong effect on ecosystems. Intraguild predation may contribute to the decline in the distribution, abundance and population size of native species and may facilitate the spread of non-native taxa. In this study, we investigated the feeding ecology of the invasive fish Amur sleeper (Perccottus glenii Dybowski, 1877) in a lowland watercourse, where it co-exists with the threatened native fish European mudminnow (Umbra krameri Walbaum, 1792). We used two sampling protocols that differed in the frequency of sampling time (e.g. monthly samplings and samplings in 10-day intervals) to provide evidence of predation, an interaction that may lead to the decline of mudminnow populations with the spread of the Amur sleeper. Aquatic macroinvertebrates comprised a major part of the diet for both sampling intervals. However, finer temporal resolution revealed the importance of fish, especially mudminnow juveniles, as a periodically available...

In May 2012 appearance of a fish species was observed in the Tisza-tó (Kisköre reservoir) near Ti... more In May 2012 appearance of a fish species was observed in the Tisza-tó (Kisköre reservoir) near Tiszafüred that prior to that had not been known from the Tisza river. On the basis of morphological examination of ten speciemens as well as genetical examination of two specimens it was proved that the new species inhabiting the river is the Caucasian dwarf goby (Knipowitschia caucasica) of ponto-caspian origin. In the case of the population found on the new locality-in opposition to the majority of populations of the species-the posterior oculoscapular canal can be seen as furrow. It confirms that the presence of this canal-an important aspect in the keys actually used-is not suitable for partition of the species. The local population probably originates from the stock inhabiting the Black Sea to which shows the closest genetic relation. It might come to the Tisa river through the lower reaches of the Danube, similarly like the tubenose goby (Proterorhinus semilunaris) and the monkey goby (Neogobius fluviatilis), but on the basis of detection of the species in the Szamos river in 2009 the spreading from the upper reaches of the water catchment area be supposed. Kivonat 2012 májusában egy olyan halfaj megjelenését észleltük a Tisza-tó (Kiskörei-víztározó) tiszafüredi szakaszán, amely a Tiszából korábban nem volt ismert. Tíz példány morfológiai és két példány genetikai vizsgálata alapján bebizonyosodott, hogy a folyó új halfaja a ponto-kaszpikus elterjedésű kaukázusi törpegéb (Knipowitschia caucasica). A lelőhelyen talált populációnál-ellentétben a fajba tartozó populációk többségével-a hátsó okuloszkapuláris csatorna helyén csupán egy árok található. Ez megerősíti, hogy e csatorna megléte-ami a jelenleg használatos határozókulcsokban fontos alternatíva-nem alkalmas a faj elkülönítésére. A helyi populáció a faj Fekete-tengerben élő állományából származhat, mert genetikailag ehhez áll a legközelebb. Nem kizárt, hogy a tarka gébhez (Proterorhinus semilunaris) és a folyami gébhez (Neogobius fluviatilis) hasonlóan a Duna alsó folyása felől érkezett a Tiszába, de a 2009. évi szamosi észlelés alapján feltételezhető, hogy a vízgyűjtő fölső szakaszáról terjed. Bevezetés 2012. május 25-én a Tisza-tó tározóterének tiszafüredi partszakaszán (1. ábra: 2) egy olyan halfaj került elő, amely a Tiszából korábban nem volt ismert. Az ezt bejelentő rövid hír szerint (Harka et al. 2012) valószínűleg itt is az a kaukázusi törpegébként (Knipowitschia caucasica) azonosított faj jelent meg, amelynek a Kárpát-medencéből eddig csupán egyetlen

Ecosystem Health and Sustainability

Various types of ground baits are loaded to lakes by anglers, but the ecological role of these ma... more Various types of ground baits are loaded to lakes by anglers, but the ecological role of these materials is often overlooked. Thus, the aims of this study were to conduct a quantitative and qualitative assessment of the baits used by anglers in the largest lake of Central-Europe (Lake Balaton, Hungary), estimate the annual nutrient balance of recreational fishing, and relate the nutrient loading from this source to the total external load. Our study demonstrated that popular angler baits varied substantially in their nutrient contents and in their molar nitrogen to phosphorus (N:P) ratios. The net nutrient balance of recreational fishing was +19.3 t total N year −1 and +5.2 t total P year −1 , equivalent to 0.7% and 3.2% of the estimated total annual N and P loads, respectively. The rate of nutrient loading may be doubled if the present trends continue: anglers will use 20% more bait with an even higher nutrient content and will also show higher propensity to release the fish after ...