MICRO-ALGAE AS A SOURCE OF NUTRIENTS

Transcription

1 J. Gen. Appl. Microbiol. Vol. 1, No. 2, 1955 MICRO-ALGAE AS A SOURCE OF NUTRIENTS FOR DAPHNIDS ATSUSHI WATANABE, RYUTA ITO AND TSUTOMU SASA (The Iatrochemical Institute of the Pharmacological Research Foundation, and The Tokagawa Institute for Biological Research) Received for publication, Feb. 10, 1955 The possibility of using mass-cultured micro-algae as human food or feed for live-stocks has been the subject of a number of recent investigations. Especially with regard to Chlorella, its palatability as human food~7) as well as good nutritive value as feed for rats and chickens have been ascertained "4. As to the applicability of micro-algae as a feed for aquatic animals, however, little investigation has been done except that by Loosanoff and Engle(6) who studied the possibility of feeding oysters with Chlorella, Nitzchia, Euglena etc. The present work deals with an attempt of using micro-algae as nutrients for water-fleas, daphnids, which are known to be a favourite food for many fresh-water fish. It might be expected that if some algae are proved to be a good nutrient for daphnids, and even if they are not directly eaten by the fish, they will indirectly promote the growth and proliferation of coexisting fish. In the literature there are already some descriptions on the favorable effect of algae in accelerating the growth of daphnids~3'5>, but they were only based on non-quantitative observations made with inpure and unspecified cultures of algae. In this study we used pure cultures of different strains of algae, and the rate of multiplication of daphnids was followed quantitatively by counting the number of their individuals in each culture. EXPERIMENTAL The daphnids cultured were Daphnia longispina and Moina macropa, and the algae tested were three species of green algae, Chlorella ellipsoidea, Scenedesmus obliquus and Chlamydomonas sp., and two species of nitrogenfixing blue-green algae, Nostoc muscorum and Tolypothrix tenuis. The culture was made in a series of Erlemmeyer flasks (300 ml each in capacity) containing 1,00 ml each of filtered pond water as culture medium. After inoculating in each flask a definite number of daphnia together with a definite or varying quantities of algal cells, the cultures were placed at room temperature (21 '.'26 C) under diffuse daylight, and the growth of daphnids was followed by counting at intervals the number of their individuals in each flask. 137

2 138 A. WATANABE, R. ITo and T. SASA VOL. 1 Table 1. Effect of provision of of Daphia various algae on the longispina. proliferation In Table 1 are shown the results of experiment, in which Daphnia longispina was grown in the presence of a definite quantity (0.021 g in dry weight) of fresh cells of different algae. At the start of the experiment, each flask constained 10 individuals of Daphnia, which, in the absence of added algal cells, showed practically no increase in the 7 days of culture. A profuse growth occurred in the presence of Scenedesmus, Chlorella and Chlamydomonas. Compared with these unicellular algae, Nostoc and Tolypothrix, both being filamentous algae, were found to be less effective in promoting the growth of the daphnids. Such a difference may, presumably, be due to the difference in size and shape of algal cells, rather than to the difference in their chemical composition~2 8) or "taste ". No doubt, the unicellular algae may be easier to be eaten and digested by the organism than the filamentous ones. Table 2. Proliferation of Moina macropa in the varying concentrations of Chlorella. presence of In the next experiment, 10 individuals fed with fresh cells of Chlorella of varying tions applied were, on a dry weight basis, 100 ml, respectively. The results obtained It may be seen that, in the presence of the the growth curve ascended steadily until whereas in lower populations of algal cells each of Moina macrota were concentrations. The concentra g, g and g per are shown in Table 2 and Fig, 1. highest concentration of algae, the 14th day of the culture, the curve decended markedly

3 955 Micro-algae as a Source of Nutrients for Daphnids 139 Fig. 1. Proliferation of Moina macropa in the presence of varying concentrations of Chlorella. The figures on each curve indicate the quantity of Chlorella added to 100 ml of culture. after the 7th day of the culture. The drop of the curves may be attributed to the exhaustion of algal cells, which is indicated by the disappearance of green colours at later stages of culture. A similar experiment was performed with Daphnia longispina using g and g (per 100 ml) of Chlorella. Also in this case the number of individuals increased at first markedly, but later decreased owing to the consumption of algal cells. In the experiment shown in Table 3 and Fig. 2, Daphnia was cultured in three runs with the provision of : (1) Chlorella alone (0.021 g per 100 ml); (2) Tolypothrix alone (0.021 g per 100 ml); and (3) the mixture of Tol ypothrix (0.021 g) and Chlorella ( g). The following facts were observed in this experiment. In (1), the number of Daphnia increased steeply during the first 3 days, after which, however, it gradually decreased to become almost zero on the 14th day of the culture. In (2), the initial growth rate was considerably lower than that observed in (1), but the number of individuals increased steadily without showing decrease at later stages of culture. In the simultaneous presence of Chlorella and Tolypothrix, the initial growth rate was almost equal to that in (1), and the rate at later stages of culture was equal to that observed in (2). It is evident from these results that Daphnia eats Chlorella preferably to Tolypothrix, and that the latter, although eaten only slowly, supports the growth of Daphnia longer than the former.

4 140 A. WATANABE, R. ITo and T. SASA VOL. 1 Table 3. Effect of provision of Chlorella and Tolypothrix proliferation of Daphnia lorcgispina. on the Fig. 2. Growth of Daphnia in the filtrated pond water, which Chlorella and Tolypothrix were added together separately. The quantities of algae added to 100 ml culture were: Chlorella, g; Tolypothrix, g. to or of SUMMARY AND DISCUSSION The experimental data presented above show clearly that the unicellular algae such as Chlorella, Scenedesmus and Chlamydomonas, are excellent feed for daphnids. Although less effective than these algae, filamentous blue-green algae Tolypothrix and Nostoc, also serve as nutrient for daphnids. For the past several years we have been conducting experiments of seeding Tolypothrix and other nitrogen-fixing blue green algae on the paddy-field in order to test the possibility of increasing rice crop by virtue of their nitrogen-fixing capacity~9~. One of the serious problems arising in these field-experiments was that, occasionally, the seeded algae dissappeared

5 1955 Micro-algae as a Source of Nutrients for Daphnids 1411 completely from the field within 1 or 2 weeks In such cases we found, almost without exception, that the field water became abundant first with unicellular algae such as Chlorella and Scenedesnzus, and then with waterfleas which eventually ate up the seeded blue-green algae. We learn from the above experiments that in order to assure the growth of nitrogen-fixing blue-green algae in the paddy-field, some measure must be taken to prevent the growth of water-fleas or to suppress the growth of unicellular green algae which remarkably favors the increase of the population of daphnids. REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) CoMBs, G. F.: Algae (Chlorella) as a source of nutrients for the chick. Science, 116, 453, (1952). FowDEN, L.: Amino acids of certain algae. Biochem. J., 50, 355, (1951). GALTSOFF, P. S.: Culture method for invertebrate animals, (New York). GEOGHEGAN, M. J.: Experiments with Chlorella at Jealott's Hill, in algal culture from laboratory to pilot plant, edited by John S. Burlew, Carnegie Institution of Washington Publication, No. 600, (1953). HIYAMA, Y.: Culture methods of daphnids. Collecting and Bleeding, 1, 324, (1939). (in Japanese). LOOSANOFF, V. L. and ENGLE, J. B.: Effect of different concentrations of micro-organisms on the feeding of oyster (0. virginica). Fishery Bull. of the Fish and Wildlife Service, United States Dept. of the Interior, 51, 31, (1947). MORIMURA, Y. and TAMIYA, H.: Preliminary experiments in the use of Chlorella as human food. Food Technology, 8, 179, (1954). 1'9 ATANABE, A.: Production in cultural solution of some amino acids by the atmospheric nitrogen-fixing blue-green algae. Arch. Bioch. and Bioph., 34, 50,. (1951). WATANABE, A., NISHIGAKI, S. and KONISHI, C.: Effect of nitrogen-fixing bluegreen algae on the growth of rice plants. Nature, 168, 748, (1951).