Istraživanja djelovanja zaraštenosti šaranskih ribnjaka emerznim makrofitima provedena su a ribnjacima ribnjačarstva D. Miholjac tijekom Ijetnih mjeseci uzgojne sezone god. 1988. i 1989. Istraživanja su provedena u šest ribnjaka, od kojih se a četiri ribnjaka (1, 2, 3 i 4) uzgajao riblji mlad, a u dva ribnjaka (5 i 6) konzumna riba. Obraštenost pojedinih ribnjaka emerznim makrofitima bila je 40 do 70 % površine ribnjaka, a prevladavala je vrsta Nymphoides peltata.
Rezultate istraživanja prikazuju tabl. 3. i 4. te sl. 1. Sadržaj kisika a vodi nezaraštenih površina varirao je unutar amplitude od 2,72 mgl-1 do 11,20 mgl-1, što upućuje na povremenu nepoželjnu razinu s gledišta potreba za normalnom prehranom i rast uzgajanih riba.
U dijelovima ribnjaka intenzivno zaraštenim emerznim biljem količina se kisika znatno smanjivala uz varijacije unutar amplitude od 1,28 mgl-1 do 7,84 mgl-1 odnosno a svim ribnjacima bila je od 0,32 do 3,84 mgl-1 (9 - 54 %) niža od količine kisika u vodi slobodnih, nezaraštenih dijelova ribnjaka. Ta je razlika bila i statistički opravdana (P < 0,05).
Rezultati ovih istraživanja upućuju na znatan negativni utjecaj emerznih makrofita a šaranskim ribnjacima. Ovisno o intenzitetu obraštenosti ribnjaka, smanjuje se i količina kisika a vodi, što smanjuje mogućnost normalne prehrane riba dodatnom hranom. Nedovoljna količina kisika a vodi rezultira slabijom iskorištenošću dodatne riblje hrane, manjim ukupnim prirastima riba i povećanim hranidbenim koeficijentom. Stoga zaključujemo da je očita važnost suzbijanja prekomjerna razvoja vodnih makrofita, ekološke skupine emerznih biljaka, a šaranskim ribnjacima.Research on the influence of emersed macrophytes in carp ponds in fish-farm D. Miholjac was carried on during the summer months of 1988 and 1989. Six carp ponds were under research: in ponds number 1, 2, 3 and 4, the fingerlings were cultured and in the ponds number 5 and 6, marketable fish. Some ponds had 40 - 70% of their area covered by emerged macrophytes, Nymphoides peltata being the dominant species.
The results are presented in tables 3 and 4 and on figure 1. The quantity of oxygen in the water of pond areas without emersed macrophytes varied between 2.72 mgl-1 and 11,20 mgl-1 indicating temporary insufficiency as far as requirements for normal growth were concerned.
In extremely overgrown areas of the ponds, the quantity of oxygen decreased significantly varying within an amplitude from 1.28 mgl-1 to 7,84 mgl-1. As opposed to pond areas free of weeds, the quantity of oxygen was 9 - 54% lower (from 0.32 mgl-1 to 3.84 mgl-1) in overgrown parts of pond areas. The fact was even significant statistically (p < 0.05).
The results indicate significantly negative influence of emersed macrophytes on the carp ponds. The oxygen level in water becomes lower as the overgrowth of the pond area becomes more extensive. That makes the possibility of otherwise normal fish feeding by additional food less convenient. Without the additional food, total fish mass increments are lower, and the food coefficient becomes higher. All of this shows the importance of reducing the overdevelopment of emersed macrophytes in the carp ponds. Therefore, the uprooting of emersed macrophytes from carp pond areas in of utmost importance
