Ishrana i značaj grabljivih vrsta riba u održanju stabilnosti ekosistema akumulacija
Feeding and importance of predatory fish species in maintenance of ecosystem stability in reservoirs
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Poznavanje ishrane riba je neophodno za utvrđivanje trofičkog statusa
ekosistema i ekološke niše riba unutar tog ekosistema i korisno je za razumevanje ekologije vrsta u cilju održivog upravljanja i razvoja mera očuvanja i zaštite određenih vrsta. Analiza ishrane riba zasnovana na analizi sadržaja digestivnog trakta predstavlja standardnu praksu. Detaljna analiza ishrane riba doprinosi razumevanju trofičkih interakcija u vodenim ekosistemima i lancima ishrane vodenih organizama. Takođe, ishrana riba predstavlja integraciju veoma važnih ekoloških komponenti koje uključuju ponašanje, kondiciju, osobine staništa, potrošnju energije, interspecijske i intraspecijske odnose. Predatorstvo je jedan od glavnih međusobnih uticaja u životinjskim
populacijama. U slučaju da se javi u vodenim ekosistemima, među ribljim
populacijama, utiče na funkcionalnost celog ekosistema. Predatorstvo od strane
grabljivih riba može drastično da redukuje gustinu i biomasu planktivornih riba,
naročito juvenilni...h primeraka, kao i odraslih primeraka koji su manjih dimenzija.
Grabljive ribe se nalaze na kraju lanca ishrane i imaju ključnu ulogu u
strukturiranju populacija vrsta na nižim trofičkim nivoima. Prekomeran razvoj
fitoplanktona je jako nepoželjan simptom eutrofizacije, stoga ekolozi tvrde da
grabljive ribe, svojim životnim procesima, mogu da smanje efekat planktivornih
riba na zooplankton i time ublaže neke od simptoma eutrofizacije.
Istraživanje za potrebe izrade ove doktorske disertacije je sprovedeno tokom
2011. i 2012. godine, a deo uzoraka je prikupljen i tokom terenskog rada u 2017.
godini. Analizirana je ishrana adultnih jedinki četiri grabljive vrste riba i to
smuđa, grgeča, štuke i soma, kao i juvenilnih jedinki grgeča, bodorke i uklije,
prikupljenih sa šest akumulacionih jezera u Srbiji: Bovan, Gruža, Šumarice,
Vrutci, Vlasina i Gazivode. Za analizu ishrane riba korišćene su tehnike
kvalitativne i kvantitativne metode i izračunati su indeksi ishrane: Indeks
relativne važnosti, Indeks značajnosti i Indeks preklapanja hranidbenih navika.
Ciljevi postavljeni tokom ovog istraživanja bili su: istraživanje ishrane
četiri vrste grabljivih riba (smuđ, grgeč, štuka i som) koje koegzistiraju uistraživanim akumulacijama; istraživanje ishrane juvenilnih riba (piscivornih i
planktivornih), kao značajnih karika u lancu ishrane proučavanih ekosistema;
istraživanje interspecijske i intraspecijske kompeticije u ishrani istraživanih
vrsta, odnosno odrediđivanje stepena preklapanja prehrambenih navika (preklapanje
trofičkih niša); procena uticaja predatorskih vrsta riba na riblju mlađ;
određivanje procentualnog odnosa grabljive - ostale ribe u ihtiocenozama u
istraživanim akumulacijama; sprovesti novo istraživanje sa ciljem utvrđivanja koje
grabljive ribe svojim životnim procesima utiču na ekološku stabilnost
akumulacija (koncept trofičke kaskade).
Primarni plen juvenilnim jedinkama je zooplankton, s tim što je uklija
obligatni planktivor, bodorka i planktivor i bentivor, dok je juvenilni grgeč
planktivor, bentivor i piscivor. Najdominantnija hrana jedinkama juvenilnog grgeča
su kopepode i kladocere, ali u različitim proporcijama. Zabeleženo je i da se grgeč
pri starosti 0+ hrani ribom. Juvenilni primerci bodorke su bili prisutni u
mrežama tokom izlova na svih šest akumulacija obuhvaćenih ovom studijom. Plen
koji je najčešće bio prisutan u digestivnom traktu ovih jedinki su kladocere
(Daphnia sp. i Bosmina sp), dok su na akumulaciji Bovan uz njih još prisutne i
kopepode. Izuzetak su jedinke uzorkovane sa akumulacija Šumarice i Gazivode kojima
su najfrekventniji plen končaste alge. Uklija najčešće kao plen bira kladocere,
Daphnia sp. i Bosmina sp., ali u različitoj meri.
Smuđ, kao najbrojnija grabljivica u istraživanju, skoro isključivo u ishrani
koristi ribu. Uklija je plen koji se izdvaja kao najdominantniji, a uz nju, smuđ se
najčešće hrani još i bodorkom, grgečom. Grgeč na svim akumulacijama u ishrani
koristi ukliju, a uz nju, hrani se često i bodorkom i jedinkama svoje vrste. Grgeč je
jedina vrsta u istraživanju u čijim populacijama je konstatovana pojava kanibalizma.
Štuka je najmanje brojna vrsta u ovom istraživanju prisutna na dve akumulacije,
Bovan i Šumarice. Ishrana ove grabljivice je najmanje raznovrsna i čine je
isključivo ribe, bodorku i grgeča najčešće. Som je bio prisutan na svim
istraživanim akumulacijama, osim na Šumaričkoj i Gazivodskoj akumulaciji. Jedino
je na akumulaciji Vrutci ubedljivo najdominantniji plen bila babuška, dok je svim
ostalim to grgeč. Grgeč je bio prisutan u svakom analiziranom uzorku crevnog trakta
soma na akumulacijama Bovan, Gruža i Vlasina.
The knowledge of fish diet is necessary to determine the trophic status of the
ecosystem and the ecological niche of fish within that ecosystem and is useful for understanding ecology of species in order to sustainably manage and develop measures for the preservation and protection of certain species. The analysis of fish diet based on analysis
of digestive tract content is a standard practice. A detailed analysis of fish diet contributes to
the understanding of trophic interactions in aquatic ecosystems and food chains of aquatic
organisms. Also, fish diet is the integration of very important ecological components that
include behavior, fitness, habitat characteristics, energy consumption, interspecies and
intraspecies relationships.
Predation is one of the major interactions in animal populations. In case it occurs in
aquatic ecosystems, among the fish populations, it affects the functionality of the whole
ecosystem. Predation by piscivorous fish can drastically reduce the d...ensity and biomass of
planktivorous fish, especially juvenile specimens, as well as adult specimens that are smaller
in size. Predatory fish are at the end of the food chain and play a key role in the structure of
populations of species at lower trophic levels. Excessive development of phytoplankton is a
highly undesirable symptom of eutrophication, therefore, ecologists maintain that predatory
fish, by their life processes, can reduce the effect of planktivorous fish on zooplankton and
thus reduce some of the symptoms of eutrophication.
The research for the needs of this doctoral dissertation was conducted during years
2011. and 2012., and a part of the samples was collected during fieldworks in 2017. The
feeding of adult specimens of four species of predatory fish was analyzed, including the
pikeperch, Eurasian perch, pike and European catfish, as well as the juvenile specimens of
the Eurasian perch, roach and bleak, collected from six reservoirs in Serbia: Bovan, Gruža,
Šumarice, Vrutci, Vlasina and Gazivode. For the analysis of fish diet, techniques of
qualitative and quantitative methods were used, and food indices were computed: The Index
of Relative Importance, Prominence Value and Schoener’s diet overlap index.
The aims of this study were: Researching the diet of four species of predatory fish
(pikeperch, Eurasian perch, pike and European catfish) that coexist in the investigated
reservoirs; Researching the diet of juvenile fish (piscivorous and planktivorous), assignificant links in the food chain of the studied ecosystems; Researching of interspecies and
intraspecies competition in the nutrition of investigated species, i.e. determining the degree of
overlapping of feeding habits (overlapping of trophic niches); Assessment of the impact of
predatory fish species on young-of-the-year fish; Determining the percentage ratio of the
predatory - other fish in ichthyocenoses in the investigated reservoirs; Conducting of new
research to determine which piscivorous fish influence the ecological stability of reservoirs
(the concept of trophic cascade) through their life processes.
Primary prey to juvenile species is zooplankton, bleak is obligatory planktivorous,
roach is planktivorous and bentivorous, while the juvenile Eurasian perch is planktivorous,
bentivorous and piscivorous. The most dominant preys of the juvenile Eurasian perch are
copepods and cladocera, but in different proportions. It is also noticed that the Eurasian perch
at the age of 0+ feed on fish. Juvenile specimens of roach were present in the nets catchment
on all six accumulations covered by this study. The prey that was most commonly present in
the digestive tract of these individuals are the Cladocera (Daphnia sp. and Bosmina sp), while
on the Bovan resrvoir there are also copepods. The exception are the individuals sampled
from the Šumarice and Gazivode reservoir, which most frequent feed on algae. Bleak most
often as a prey choose cladocera, Daphnia sp. and Bosmina sp., but to varying degrees.
Pikeperch, as the most abundant predator in the research, in diet use almost
exclusively fish. Bleak is the prey, which is distinguished as the most dominant, and besides
it, pikeperch are most often fed by the roach and Eurasian perch. The Eurasian perch on all
reservoirs in the diet use the bleak, and along with it, it is often fed on roach and the
specimens of their own species. Eurasian perch is the only species in the research in whose
populations is noticed the phenomenon of cannibalism. Pike is the least numerous species in
this study present on two reservoirs, Bovan and Šumarice. The diet of this predator is least
varied and makes it exclusively fish, most often roach and Eurasian perch. European catfish
was present on all researched reservoirs, except on Šumarice and Gazivode reservoirs. Only
on the Vrutci reservoir the most dominant prey was a prussian carp, while all other specimens
of European catfish had Eurasian perch as dominant prey. Eurasian perch were present in
every analyzed sample of the intestinal tract of the European catfish on the Bovan, Gruža and
Vlasina reservoirs.