Influence of abiotic and biotic environmental factors on weight gain of cultured carp on a carp farm

Abstract

During the period from April to October in the production season of the year 2000, seven chemical parameters of the aquatic environment were analyzed twice a month for the amount of natural food (zooplankton and bottom fauna) on pond No. 4 at the Dubica Carp Farm in Banatska Dubica (Vojvodina, Serbia). Correlation between natural food and carp growth was analyzed as well. The investigations revealed negative correlation between the amount of natural food per kilogram of ichthyomass and pH (p lt 0.001, r = -0.875), electroconductivity (p = 0.0294, r = -0.673), COD (p = 0.0052, r = -0.782), total water hardness (p = 0.0186, r = -0.709), and carbonate water hardness (p = 0.0087, r = -0.758). However, statistically significant positive correlation was found between the biomass of natural food (g/kg of ichthyomass) and concentration of nitrates (p lt 0.01, r = 0.841) and phosphates (p = 0.0427, r = 0.640). Concerning com­ponents of natural food (zooplankton and bottom fauna), bottom fauna biomass had a very low production and showed no statistically significant correlation (p = 0.137, r = 0.491) with total natural food biomass whereas zooplankton biomass was very significantly correlated (p lt 0.001, r = 0.830) with the total amount of natural food, indicating that zooplankton was the dominant component of natural food at the investigated fish pond. The daily weight gain (%) of cultured fish was greatest at the beginning of the carp farming season, i.e., in April, when it comprised a value of 2.3%. After negative growth at the end of May (-0.2%), a gradual increase of weight gain was recorded until the beginning of September. By comparing the biomass of natural food with the daily weight gain (%) of carp, it was observed that the weight gain had a trend similar to biomass of natural food with a 15 day interval. This relationship was justified by positive statistical correlation (p = 0.006, R = 0.960). As zooplankton was the major component of natural food, fish relayed on it as the main protein source showed by a significant positive correlation (p = 0.034, r = 0.907).

U toku proizvodne sezone 2000. godine, u periodu od aprila do septembra, dva puta mesečno, vršena je analiza sedam hemijskih činioca vodene sredine u korelaciji sa dinamikom prirodne hrane (zooplanktona i faune dna), kao i korelacija između prirodne hrane i dinamike rasta šarana u ribnjačkom objektu br. 4, šaranskog ribnjaka 'Dubica' iz Banatske Dubice, Srbija. Istraživanja su pokazala negativnu korelaciju između: pH (p lt 0,001, k=-0,875), elektro­provodljivosti (p=0,0294, k=-0,673), HPK (p=0,0052, k=-0,782), ukupne tvrdoće vode (p=0,0186, k=-0,709), karbonatne tvrdoću vode (p=0,0087, k=-0,758) i količine prirodne hrane (zooplanktona i faune dna) iskazane po kilogramu ihtiomase. Statistički značajna pozitivna korelacija konstatovana je između koncentracije nitrata (p lt 0,001, k=0,841) i ortofosfata u vodi (p=0,0427, k=0,640) i količine prirodne hrane po kilogramu ihtiomase. Posmatrajući odnos komponenti prirodne hrane: zooplanktona i faune dna prema ukupnoj količini prirodne hrane, bio­masa faune dna ne pokazuje statističku značajnu korelaciju (p=0,137, k=0,491) sa ukupnom biomasom prirodne hrane po kilogramu ihtiomase, dok biomasa zooplanktona pokazuje značajnu korelaciju (p lt 0,001, k=0,830) sa ukupnom količinom prirodne hrane (izražene po kilogramu ihtio­mase), a što ukazuje na činjenicu da je u ispitivanom ribnjaku dominantna komponenta prirodne hrane zooplankton. Dnevni procentualni prirast gajene ribe bio je najveći početkom sezone gajenja šarana tj. u aprilu -2.3%. Posle negativnog prirasta krajem maja (-0.2%), zabeležen je postepeno povećanje prirasta sve do početka septembra. Komparacijom biomase prirodne hrane (izražene po kilogramu ihtiomase) i procentualnog dnevnog prirasta šarana, konstatovano je da prirast šarana najčešće prati količinu prirodne hrane, tako što se beleži povećanje prirasta 15 dana nakon povećanja bio­mase takve hrane.