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

In the third experimental pond (Rotatoria breed III), from 22.09 to 19. 10 the average water temperature was between 18 and 20°C. Considering that in this breed the maximum abundance values did not exceed 200 ind./lit. , we do not go into details, we recorded it only among the diagrams of comparison (Fig. 1). B ) Moina brachiata breed The results of the breed in the first experimental pond are shown in Table 3 and Figure 1. In the period between 21.07 and 11.08 the water temperature varied from 22 to 24°C, which was fairly favourable for the Moina population. The maximum abundance of the Moina population occurred on the 11th day after the introduction. 12 55. 1 individuals were found in one litre of water in this case. In the period of intensive reproduction the stock was able to double its total number daily. We found the biggest average number of eggs on the 4th day, it was 18 eggs/female, which gradually decreased as the population grew old. During the time of breeding it was in the starting period that we found the maximum number of eggs in one female, which was 2 6 eggs. The ageing of the population occurred during the 4th week of the experiment. At the end of the 3rd week, Daphnia magna and Cyclops species appeared with an increasing abundance. The appearance and multiplication extraneous species indicate the severe deterioration of the pure breed, and also the unfavourable change of environmental conditions. In the intensive period of reproduction as far as reaching the maximum number of individuals, the population was made up of females with eggs and young individuals with eggs and young individuals producing eggs only later. However, on reaching the peak of gradation, there appeared more and more females no longer producing eggs and also males, and ephippial females. The maximum number of male individuals occurred 2 days before and with a higher value than that of the ephippial females. In the breed Moina II from 14.08 to 08.09 the water temperature was lower (20 to 22°C), thus, the maximum abundance was also lower (720.0 ind./lit. ), and the time of appearance was shifted, too (Table 4 and Fig. 1). The formation of the breed Moina III. after the introduction of the basic population was unsuccessful because of the marked decrease in water-temperature and alga-production (Fig. 1). C ) Daphnia magna breed We indicated the changes taking place in the first experimental pond in Table 5 and Fig. 1. During the breed, the water-temperature was generally between 22 and 24°C (from 29.07 to 22. 08). The maximum abundance of Daphnia magna occurred on the 15th day after the introduction, when 1502. 9 ind./lit. were found. During the breed it was in the starting period that we found the maximum number of eggs in one female, which was 52. The biggest average number of eggs was found on the 6th day with the value of 30, 5 eggs per individual, and which decreased to 0 on the 17th day. From the average values for the egg-number one can see that at this time the population was strongly deteriorating from the point of view of population reproduction. In the starting period, then, in the period of intensive reproduction, in the breakdown of the population by age, the highest percentage is represented by the juvenile individuals. The exterior features also prove that the conditions were good. The transient, oily colour of the gut contents and the wall of the intestines, and the numerous small dark oily coloured eggs testify optimal conditions (KONOVALOV, 19 55). Even in the case of maximum reproduction, the brood pouch of some percent of the adult individuals is empty in the stock. This observation is precisely supported by the experiments by WOYNÁROVICH (1958). The males and the ephippial females appear before the population reaches complete maturity, their maximum abundance coincides with the gradation value of the population. Here, too, the number of the male individuals is much bigger than that of the fecundable females. In the second breed (Table 6, Fig. 1) set up at a later time (from 14.08 to 08.09) under less favourable nourishment and temperature conditions, we experienced the decrease of the abundance and also that the maximum value occurred later. In breed Daphnia III (from 27. 09 to 21. 10) with the water being 18 to 20°C, the population was unable to multiply in a large number, the number of individuals was under 100 ind./lit. all the time, so its results are shown only in Figure 1.