Østersens respirasjon - Undersøkelser utført ved Statens Utklekningsanstalt Flødevigen

Abstract

In Norway the oyster, Ostrea edulis, is cultivated in small natural salt-water ponds, with but narrow communications with the sea. On the top of the ponds we have generally a layer of fresh water. The temperature rises very high during summer - to 25° C or even higher. In winter the ponds may be covered by ice for about 5 months. And especially on the Skagerrak coast the temperature of the sea water may approach zero. During summer the production of phytoplancton is very high. And the quantity of oxygen produced may often exceed 150 per cent of saturation. In autumn the sunlight becomes scarce, the oxygen will be consurned to a high degree, and hydrogen of sulphur may occur in the bottom layers. It will be understood that the oysters in these ponds must be in possession of a great power of adaptation to different environments. In the present paper are given the results of experiments on the consumption of oxygen, and the production of carbondioxide by the oyster at different temperatures. The oysters used were taken from the same batch. They were partly brought directly into the experiments, and partly kept for a few days beforehand in filtered water, in order that they may rid themselves of contents in the intenstines that might impair tlie analysis. Prior to the experiments the oysters were brushed and washed with 40 per cent alcohol, and oysters intended for use in series in the experiments were numbered. The experiments were performed in glasses containing 2 litres of sea water. They were closed water-tight by means of glasslids, rubber bands and springs. During the experiments the glasses had to be turned in order to bring about circulation. To prevent small bits of shell to be broken off and come into the analysis for carbondioxide, the oysters were wrapped in pieces of gaze. In each experiment were used several oysters, kept in separate glasses. In order to eliminate the changes occasioned by the life processes of the plancton and the bacteria in the sea water used, glasses filled with the same water were included in the experiments. The results then represent the difference betwecn the actual sample and the blind proof. The duration of each experiment varied according to the temperature. Care was taken to stop the experiment before all the oxygen had been consumed. The results are given seperately for the individuels opened later, to determine the net weight, and for oysters kept for further experiments. In the latter the total weight was used. The chief results are given in Figs. 1-4. Fig. 1. The oysters used were kept in the rearing pond. And the closed experimental glasses were placed at a depth of one metre in the pond. The sea water in this pond was constantly renewed from a depht of approximately 15 metres below the surface. The temperature varied in conformity with the sea ternperature. The variations in the salinity were small. In the figure the temperature is given in the uppermost curve. It varied between - 1.5° and + 19.2° C. The consumption of oxygen expressed in ml of O2/100 g of total weight per 24 hrs, both in filtered and unfiltered water, runs - as might be expected - fairly parallel to the temperature. The consumption is severely lowered when the temperature falls below 5°, and equals 0 when the temperature reaches zero. The production of CO2, stated in the same terms, runs fairly parallel, the R.Q. is varying from 0.9 to 1.0. The values of R.Q. for the experiments at the lowest temperatures are not given, not being reliable. The production of CO2 in experiments with oysters in unfiltered water is not stated, the values being influenced by the excrements. At the bottom of the figure is given the average weight of the oysters used. The weight increased from June 1941 to January 1942. During the cold period the weight decreased. Fig. 2. The oysters used were kept in the oysters pond. In this basin the water was renewed when necessary. The temperature was allowed to rise, in this case to 26° C. Unlike the other basin, the quantity of oxygen rose here very high. From the diagram it will be seen that the O2 percentage in the spring of 1942 reached nearly 300. In 1941 the consumption of oxygen was what might be expected. In 1942 the values for oysters kept in filtered water was very low. It is assumed that this was occasioned by the oysters having been transfered from water with a high percentage of oxygen, 200 per cent, to filtered water with but 100 per cent. Fig. 3 gives the consumption of oxygen. All the experiments are arranged according to temperature. In the preceding figures the values have been reduced to 100 g of the total weights. In the experiments, some of the specimens were opened to determine the net weights. By means of these net weights the consumption of oxygen were here reduced to 10 g of the net weights for all the samples. Fig. 3 a contains the result obtained with unfiltered water. The consumption rises along a straight line according to temperature, except at the lowest temperatures. In Fig. 3 b we have the corresponding values for oysters kept in filtered sea water. The values Iiere diverge very much. The pr-ocess of keeping the oysters in filtered water apparently caused some disturbances. They may have been due to variations in the temperature, and in the content of oxygen. At very low temperatures we found here no consumption of oxygen. In Fig. 4 the results of experiments with oysters in unfiltered water, carried out at Flødevigen, are parallised to the results obtained by other investigators. MITCHELL dealt with Ostrea virginica, NOZAWA with Ostrea circumpicta, and SPÄRCH with Ostrea edulis. The results obtained by MITCHELL and NOZAWA correspond to the Norwegian ones. The consumption found by SPÄRCH is much lower.