Effects of abiotic and biotic factors on fish growth in semiintensive fish production

Abstract

During 1999 investigations of effects of several abiotic (temperature, ammonia, dissolved oxygen, pH) and biotic (zooplankton and bottom fauna) factors on fish growth in a semiintensive fish production system were carried out. These investigations were carried out on a fish pond with 182 ha area on the Dubica fish farm at Banatska Dubica. Results of this study have shown that under conditions of optimal temperatures, pH values and dissolved oxygen, which occurred from the middle of May to the end of August, the strongest effect on fish growth rates was exerted by levels of zooplankton and bottom fauna production. The significance of additional feeding can be neither neglected, nor emphasized, especially if such feed­ing consists mainly of carbohydrate food stuff (wheat, corn, barley). Under conditions when additional feeding was the most intensive (second part of August), the carp growth rate decreased. The lower growth rate was due to the fact that in this period, in addition to a decrease in natural fish food, the highest ammonia content was found (1,96 mg/1). High ammonia concentra­tions in the second part of September, as well as temperature oscillations, prevented fish growth during the greater part of September.

U toku 1999. godine obavljena su istraživanja uticaja nekih abiotičkih (temperatura, amonijak, rastvoreni kiseonik, pH) i biotičkih činioca sredine (zooplankton i fauna dna), na prirast gajenog šarana u poluintenzivnom sistemu gajenja. Istraživanja su realizovana na odgajivalištu površine 182 hektara ribnjaka "Dubica" iz Banatske Dubice. Rezultati obavljenih ispitivanja ukazuju na činjenicu da, u uslovima optimalnih temperatura, pH vrednosti vode i kiseoničnog režima kakvi su konstatovani od sredine maja do kraja avgusta, na prirast ribe najveći uticaj ima nivo produkcije zooplanktona i faune dna. Ne treba zanemariti ni dodatno prihranjivanje gajene ribe, ali ni prenaglašavati njegov značaj, posebno ukoliko je takvo prihranjivanje bazirano isključivo na ugljenohidratnim hranivima (pšenica, kukuruz, ječam). Tako je u uslovima kada je prihranjivanje bilo najintenzivnije (druga polovina avgusta), prirast gajenog šarana bila smanjena. Razlozi slabog prirasta su i u činjenici da je upravo tada, pored pada količine prirodne hrane zabeležen i najviši nivo amonijaka (1,96 mg/1). Visoka koncentracija amonijaka u drugoj polovini septembra, kao i oscilacije temperatura su onemogućili prirast gajene ribe tokom većeg dela septembra.