Life history patterns of Procladius choreus, Tanypus punctipennis and Chironomus balatonicus in Lake Balaton

Life history patterns of the three most abundant chironomids were analysed in Lake Balaton by monitoring the population dynamics of larvae and the presence of pupal exuviae. Procladius choreus had two generations per year with at least two parallel cohorts during 1996-1999. Tanypus punctipennis had a trivoltine life cycle with occasional parallel cohorts, overlapping generations and long, interrupted emergence periods between 1997 and 1999. At Tihany, Chironomus balatonicus had only one detectable generation between 1995 and 2002. Meanwhile at Keszthely, the abundance of C. balatonicus larvae peaked from autumn to the beginning of summer in 1996/1997, 1998/1999 and 2000/2001, and it was continuously high from August 2001 to October 2002. However, between these abundance peaks there were long periods when larvae could not be found at all. The C extreme population dynamics of C. balatonicus suggests that living conditions may fluctuate around the limit of this species in Lake Balaton. Although C. balatonicus larvae practically were not found at both sampling sites from July 1997 to August 1998. and from July 1999 to August 2000, sporadic occurrence of exuviae during these periods proves that refuge areas should exist within the lake. Possible background of the uncommon population dynamics of C. balatonicus is discussed

Őshonos halfajok ivadékának táplálkozási stratégiája, trofikus kapcsolatai, növekedése és túlélési esélye a Balatonban: [Feeding strategy, trophic relationships, growth and survival of native fishes during their first year of life in Lake Balaton.]

Munkánk során igyekeztünk feltárni a fogassüllő, a kősüllő és a dévérkeszeg ivadék mennyiségében mutatkozó tér- és időbeni változásokat, vizsgáltuk az ivadék növekedését, mortalitását és táplálkozási szokásait. Vizsgáltuk a vízhőmérséklet változásainak hatását az ivadék növekedésére és mennyiségére. Meghatároztuk a fogassüllő, a kősüllő és a dévérkeszeg elvi termékenységét a Balatonban

Development of a fish-based index for the assessment of the ecological status of Lake Balaton in the absence of present day reference condition = Élaboration d’un indice basé sur les poissons pour l’évaluation de l’état écologique du lac Balaton en l’absence de conditions de référence actuelles

A fish-based index is proposed to indicate the ecological status of Lake Balaton, Hungary in accordance with the standard of the European Water Framework Directive (WFD). The Balaton fish index (BFI) synthetises information of 13 lake-specific fish metrics including gillnetting and electric fishing data of species richness of native assemblages, relative abundance, biomass and age structure of native key species, representation of non-native species and general health status. The main anthropogenic pressures considered were the degradation of littoral habitats, invasion of non-native fish species, eutrophication and fishing/angling including stocking. Ecological quality ratio (EQR) is assessed by relating actual fish assemblage metrics to the supposed undisturbed reference status of Lake Balaton reconstructed by expert judgement based on recent and historic information on the fish fauna and its changes. Values of BFI were consistent and indicated good ecological status of Lake Balaton in the period of 2005–2018. This study provides an example on how an EQR assessment methodology might be established in unique habitats with no possibilities for statistical evaluation of pressure-respond relationships and exact determination of the reference status

Comparative study of Gymnocephalus cernuus (Linnaeus, 1758) and G. baloni Holcik & Hensel, 1974 (Pisces, Percidae)

In the comparative study of Gymnocephalus cernuus and G. baloni we searched for differences in growth, habitat and feeding between the two species in support of their distinctness. significant differences were found in both habitat and feeding, whereas growth was more or less similar. G. baloni is bound to hiding places located in flowing water. In vegetative periods it occurs solitary and in generative in pairs. G. cernuus lives in shoals in the whole season, occuring mostly in the open, still parts of waters near to the bottom. The food of the two ruffe species mostly consists of the characteristic macroinvertebrates of their habitat. The body pattern, the number of opecular spines and the cut on the membrane between AI and AII were found to be the most useful characters in identification

Az egyedfejlődés során bekövetkező táplálékváltások és azok növekedést, illetve táplálékbázis felosztást érintő hatásainak vizsgálata balatoni halakon. = Ontogenetic diet shifts and their effects on growth and food resource partitioning in fish in Lake Balaton.

Pályázatunk célja volt, hogy elemezzük 15 gyakori halfaj (bodorka, vörösszárnyú keszeg, balin, küsz, karika keszeg, dévérkeszeg, garda, ezüstkárász, ponty, naphal, sügér, vágódurbincs, fogassüllő, kősüllő és folyami géb) táplálkozásában megfigyelhető méretfüggő folyamatokat természetes életterükben, a Balatonban. Kutatásaink során leírtuk e halfajok táplálék összetételében tapasztalható méretfüggő változásokat a táplálkozás megkezdésétől a legidősebb példányokig. Meghatározásra kerültek fajonként az egyedfejlődés során fellépő táplálékváltások, értékeltük azok határozottságát és alternatíváit. Leírtuk az egyedfejlődés során bekövetkező táplálékváltások hatását a fajon belüli (méretcsoportok közötti) táplálékfelosztásra és eredményeinket újszerű grafikus eljárással szemléltettük. Meghatároztuk a vizsgált halközösségen belül fennálló funkcionális táplálkozási csoportokat figyelembe véve a táplálékváltásokat is. Részletesen értékeltük a fajok közötti táplálékmegosztást és leírtuk a potenciálisan versengő csoportokat. A növekedési mutatok, a táplálékfejlődés és a táplálékkészlet alapján értékeltük az egyes halfajok életfeltételeit a Balatonban. Végül, az eredmények tükrében javaslatot tettünk a fogassüllő és a ponty célszerű telepítési méretére vonatkozóan is. | Aim of this project was to analyse size-dependent patterns in feeding ecology of 15 common fish species (roach, rudd, asp, bleak, white bream, common bream, razor fish, gibel, common carp, pumpkinseed sunfish, perch, ruffe, pikeperch, Volga pikeperch and monkey gobby) under natural circumstances, in Lake Balaton. We described size-related changes in the diet of these species from the beginning of exogenous feeding to their oldest age groups. We defined ontogenetic diet shifts in each species, assessed their flexibility/rigidity and their alternatives. We described effects of the ontogenetic diet shifts on inter-specific (among size groups) food partitioning and we visualised these results with a novel graphical method. We analysed the functional feeding guild structure of the studied fish assemblage considering also size-dependent processes as well as ontogenetic diet shifts. Inter-specific diet partitioning was studied in details and potential competitive relationships were characterised. According to growth parameters, diet ontogeny patterns and food resources we discussed living conditions of specific fish species in Lake Balaton. Finally, based on our findings we gave suggestions for optimal stocking sizes of pikeperch and common carp in Lake Balaton

Management of pikeperch stocking in Lake Balaton: effect of season, area, fish size and method of release on the rate and distribution of recaptures

Pikeperch Sander lucioperca is an economically important fish which depleted populations need intensive management and supplemental stocking. We aimed to assess the relative influence of various pikeperch stocking strategies in Lake Balaton, Hungary, and tested 60 stocking set-ups (two seasons × three lake areas × shore vs. offshore release × five size groups) by releasing 3000 tagged yearlings. Anglers reported data of 522 recaptures within four years after stocking. Recapture rate was highest in stocking of the most productive lake area, increased with fish size, was higher in shore than offshore releases, but did not differed between stocking seasons. Fish stocked to oligotrophic areas travelled longer distances and dispersed more than those stocked to the mesotrophic area. Fish size had little effect, whereas season and method of stocking had no effect on dispersal of fish. To conclude, in pikeperch, autumn stocking with large yearlings released directly from the shore is recommended over other set-ups. Stocking quotas may be concentrated in space in low productivity areas, but should be dispersed between multiple sites in food rich areas to attain complete dispersal. This study provides a framework for testing fisheries management alternatives and behaviour of stocked fish in intensively utilized habitats

A fogassüllő és a kősüllő szaporulata a Balatonban. [Natural recruitment of pikeperch and Volga pikeperch in Lake Balaton.]

Jelen közleményünkben a fogassüllő és a kősüllő ivadék mennyiségi viszonyait, túlélési esélyét és növekedését mutatjuk be ötéves adatsoraink alapján a Balatonban. Tárgyaljuk a fogassüllő ivadék telepítések célszerűségét és hatékonyságát a természetes szaporulat tükrében

Effects of the diversion of the Danube on two ruffe species in the Szigetköz area

After the diversion of the Danube, the resulting habitat loss and alteration negatively affected the condition of the surviving populations of two ruffe species. The oldest individuals appeared to be most sensitive to these changes. Because of these alterations, the future existence of Gymnocephalus baloni in the Szigetköz area seems doubtful