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
the soil of the ponds. After this, simultaneously with the slow flooding, 200 kg of pig manure, 3 kg of urea and 1. 5 kg of phosphorous fertilizer were added to the water of each pond. To sift out the Cladocera spp. and wild fishes, the water was let in through a plastic sieve. When 0.8 m deep, the water of the ponds was treated with 1 ppm concentration of insecticide "Flibol-E" with trichlorfon as the agent so as to guarantee the selective preparation for rotifers. This substance destroys the planktonic Crustacea species, so only the Rotatoria spp. remain alive and form a basic stock in the water of the pond (TAMÁS and HORVÁTH, 1972, 1974, 1975). Since the effect of "Flibol-E", lasting for five to six days, destroys planktonic Crustacea, it was only afterwards that the basic populations of Moina brachiata and Daphnia magna were introduced in the Cladocera breeds. 1000 mature female individuals with eggs were introduced into each pond on the 6th day after their filling up in the case of the Moina I , II , III and the Daphnia II , III breeds; and on the 9th day in the case of the D aphnia I. breed. When sampling on every 3rd day as an average, 20 litres of water were ladled with a one-liter graduate from ten given places of each pond. The sample filtered through the plank ton-sieve was fixed and stored in 4% concentration of formalin until processing. During the time of experiment there were no further nutriment addition and biomass drawing. For the separation of the species, we used the books available on this topic (GULYÁS, 1974; VARGA, 1966; VOIGHT, 1956). In the present article the results of the following experimental ponds were used. The starting points indicate the flooding of the ponds in the case of the Rotatoria breeds, and the introduction of the starting population in the case of the Cladocera breeds. Rotatoria breeds: Moina bre Daphnia b I. 14. 07. 1975 0 1. 08. 1975 ( 8 samplings during 18 II. 15. 08. 1975 09. 09. 1975 (10 samplings during 25 III. 22. 09. 1975 19. 10. 1975 ( 8 samplings during 27 :eds: I. 21. 07. 1975 11. 08. 1975 (10 samplings during 21 II. 1 4. 08. 1975 OH. 09. 1975 (10 samplings during 25 III. 27. 09. 1975 2 1 . 10. 1975 ( 8 samplings during 25 reeds: I. 29. 07. 1975 22. 08. 1975 (10 samplings during 24 II. 14. 08. 1975 08. 09. 1975 (10 samplings during 25 III. 27. 09. 1975 21 . 10. 1975 ( 8 samplings during 2 5 days) days) days) days) days) days) days) days) days) Since the basis of population-dynamic investigation of a given species is the establishment of the population structure, we made regular surveys. The fact that in the examined population of the Rotatoria and Cladocera species the individual generations overlap each other, renders the analysis of the ability for reproduction of the population very difficult. From among the structural elements of the Brachionus calyciflorus populations (Tables 1 and 2) the separation of age-groups was possible only to the extent that the young, smaller individuals not producing eggs were separated from the adult individuals. Taking into consideration their way of reproduction, we separated the amictic individuals, those producing eggs without fecundation from the mictic individuals and the ephippial females. In the tables presenting the structure of the populations of the two Cladocera species (Tables 3 to 6) there were more opportunities for the separation on the ground of age and sex as a result of the endowments of the species. Thus, into the group of the reproductive females we listed individuals nursing eggs well visibly in their ovary from the more developed ones with eggs in their brood pouch. We separately counted the females which grew old and were no longer able to produce eggs. Into the group of the young or juvenile we listed the smaller individuals in the ovary of which developing eggs could not be recognized. The males, which are rare and differ from the females both in the form and the size of the body were also separated, as were the females bearing resting eggs and representing ephippium. We counted the eggs released from the brood pouch of the females with eggs; we compared the proportion of the reproductive females and young individuals to the total number of individuals.
