Hidrológiai Közlöny 1987 (67. évfolyam)

2-3. szám - Ruttkay András–Kepenyes János: Új módszer a haltermelés vízigényének számításához

RÚTTKAY A.—KEPENYES J.: Oj módszer 99 telített (vékony folyamatos vonal), illetve az ammóniamentes (vékony szaggatott vonal) vízzel szemben mennyit változik a tényleges vízáramigény (vastag vonalak). A B ábrarész az oxigénpótlás lehetőségeit mutatja (bal oldal: túltelítés, jobb oldal: levegőztetés) az ammónia eltávolításához szükséges 1,39 m

3/kg-d vízáram mellett. A G ábrarész az ammóniaeltávolítás módozatait mutatja, bal oldalon recirkuláltatás, jobb oldalon biofilter alkalmazásával. A lecsökkentett vízáram mellett az oxigénigény kielégítése a B részábra analógiájára történik. Az ábrasor egyben annak bemutatására is alkalmas, hogy az általános képletünkben miért tartottuk meg a q szorzójaként clZ OC q j CC GS z tagokat (ezek változása a halsűrűségtől független, a bal oldali ábrák vízszintes vonalai!) és amelyeket „külső" tényezőknek tekintünk. A „belső" tényezők közül az m\C és m/Z) konstans, a &-nak és az &-nek viszont csak akkor van szerepe, ha magában a haltermelő medencében befolyásoljuk az oxigént, vagy az ammóniát (a jobb oldali ábrasor). Ez esetben a fajlagos vízáram és a hal sűrűségének kapcsolatát jól érzékeltetik a hiperbolák. Irodalom Kepenyes, J., Ituttkay, A. 1983. Water requirement for fish production. Int. Con}, on Water Menagement and Production Potential in Agriculture Szarvas (Hungary), Section: A, B, D: 90—100. Liao, P. B., R. D. Mayo. 1972. Salmonid Hatchery Water *Keuse Systems. Aquaculture 1: 317—335. Speece, R. K. 1973. Traut Metabolism Characteristics and the Rational Design of Nitrification Facilities for Water *Iteuse in Hatcheries. Trans. Amer. Fish. Soc. 102: 323—334. Wheaton, F. W. 1977. Aquacultural Engineering. Wiley-Interscience, New York 1—-708. Kézirat beérkezett: 1985. május 3. Átdolgozás beérkezett: 1986. december 22. Közlésre elfogadva: 1987. március 1. A new method for calculation of water requirement of rishproduction A. Ruttkay and J. Kepenyes Abstract: For „normal" growth of fish, not only food but an adequate amount of water is needed because the oxygen requirement of fisli is supplied fromthe water, and at the same time the metabolites are excreted into the water. If the amount of oxygen is insufficient or the concentration of metabolites is high, growth rate of fish will be decreased or in a worse situation it can also occur in losses of fish. The specific water current requirement (q) is the best value for determination of water requirement of fish, that is given by eq. (1), where m is the specific metabolite production offish (g/kg -d), and C is the maximum level of metabolite concentration in the fish tank (g/m

3). The specific water current requirement of common carp in a flow-through system lias been determined experimentally. There were 20, 40, 60 and 80 kg (W

0) of fish stocked in three tanks, whero average mass of carp was 100—120 g/ind, and the flow rate was 50, 100 and 150 m

3/d (Q). The daily amount of feed was 30 g/kg -d, that was applied in 5—6 portions during daytime. Results of the experiment are shown in Table 1. The specific water current calculated from the average masses is presented in Table 2, and the specific water requirement in Table 3. On the basis of Figure 1, where the relationship between the growth rate and the specific water current is shown, it can be stated that the growth rate is not limited anymore when q is higher than 2 m

3/kg -d. The q can be modified by metabolite concentration of the inflow water (see Figure 2. A). The actual oxygen concentration is of the same effect (see Figure 2. B). The x

a is the modifying factor, it is a number without dimension explained by eq. (4) and (5), where C

0 is the metaboliteor oxygen concentration of the inflow water, C

s is the oxygen concentration at 100% saturation at a given temperature of water, D is the allowed oxygen deficiency, and 73 0 is the oxygen deficiency of the inflow water. (In general x

0 is less than 1, but it will be higher than 1 if supersaturated water is used.) Decrease of specific water requirement is a very important task for the fish culturists. It can be reached by aeration of the water in the fish tank (if the total water requirement of fish can not be fulfilled by the inflow water), or by the application of a biofilter, for the nitrification of ammonia in the fish tank, and in such a ease it is not necessary to drain all the metabolites with the outflow water. „Effieicncy" of the abovemcntioned systems is characterized by the mass transfer rate (k

). The actual decrease of water requirement is given by ratio k/S, where S is stocking density of fish (kg/m

3). These two processes are shown in Figure 3. As the water decreasing effect of the mentioned procedures is rather low, an application of a third method was taken into account. It is the partial or total recirculation of water (Figure 4), where] the purification of metabolites and oxygen saturation is carried out in a separate system. The water recycling systems are characterized by two values. One of them is the efficiency of the purification system (see (9)), where C

r is the metabolite concentration of the water outflowing from the purification system, and the other is the so called circulation value: z=Q

r/Q, that is the ratio of the circulated and the supplementary water. Based on the abovementioned statements general formulae of water requirement of fish culture are given by eq. (10). On the left side of the formula the „external" factors are written (water current, water quality), on the right side the „internal" factors aro shown, which are dependent on the fish species, its tolerance,