Dr. Éva Murai szerk.: Miscellanea Zoologica Hungarica 3. 1985 (Budapest, 1985)

Kiss, I.: Ecological studies on zooplankton species important for fish farms. I. Population biological investigations on zooplankton breeds

D ) The linear regression analysis of the growth of the populations The regression analysis of the growth of density of the individual Zooplankton populations led to the results shown in Tables 2 and 3. In the case of the two breeds of all the four species, the reliability of linear adjustment was of high degree (significant at the level of p: 0. 1 or 1.0 %). Considering that the values of "a" are proportionate to the growth of the density values of the stock, they express the relative degree of growth. We calculated species by species, how the speed of growth with the second breed changed under less favourable temperature and nourishment conditions in comparison with the first breed. The calculation was made with the following formula: m = "a" breed II/"a" breed I. If the value of "a" is low, it means that the growth of the density value reacted sensitively to the changed environmental conditions. The nearer its value is to 1.0 the smaller is the arising influence. In comparison with the first breeds, in the second breeds the value "a" of the regression line was less in each case. This change was the following in degree: species "m" Brachionus calyciflorus 0. 50 Asplanchna spp. 0.58 Moina brachiata 0.83 Daphnia magna 0. 73 The decrease is the most marked with the two Rotatoria species. The degree of the decrease is smaller in the case of the predator Asplanchna spp. (42%) than that of the prey animal (50 %). So as to clarify this observation from a different aspect, we examined how big the growth of the predators' stock was, and what was its proportion to the speed of the density growth of the prey animal. The calculation was made with the following formula: n = "a" Asplanchna / "a" Brachionus Its value was 1. 54 in the first breeding series, and 1. 77 in the second one. It means that the growth of the density value with the predator Asplanchna stock is bigger than that of the prey animal. Under less favourable environmental conditions, the proportion of the speeds of growth remained similar. SUMMARY Summing up the results of the three breeding series, we can state that in the mid-summer period (breeds I), in well-warming waters, with ample alga-production, the filter-feeder Zooplankton organisms reach an outstanding number of individuals rapidly. After a boomlike reproduction, the decline of the population follows fast, too. In the late-summer and early-autumn period (breeds II, III), the water-temperature and light conditions change, also there is a decrease of the phytoplankton in quantity as a result of which the Zooplankton populations also occur with a smaller number of individuals, the time of the gradation peak is shifted some days, and the breeds live on for a longer time. There is a close connection between the partheriogenetic egg-number and the consumed nourishment quantity of the Zooplankton species with alga-filtering activity. From the number of the eggs (embryos) found in the brood pouch of individuals in fishpond samples we could conclude back to the amplitude or insufficiency of the nourishment available in the habitat. One should remember, however, that these data reflect the situation of the state of nourishment supply at the period of the production of eggs. Comparing the maximum number of eggs which can be experimentally established to the number of eggs actually found, the degree of deviation can serve as an indicator of the production opportunities of the fishpond. The population-biological investigations of the individual Zooplankton species supported the selective plankton preparation method used on the Tempered Watered Fish-breeding Farm of Százhalombatta, with the help of which natural nourishment adequate both in size and quantity can be granted for the developing fish progeny. In the progeny breeding ponds Zooplankton breeds following each other in time can be brought about.