Studies on Fish Culture in the Aquarium of Closed-circulating System. Its fundamental theory and standard plan

Abstract

This aquarium is consist of fish tank, filter-bed, sediment-collector, circulating and aerating apparatus. The nitrogen and phosphorous cycles in aquarium are investigated and the rate of secretion of metabolites, the velocity of their decomposition are measured. And the method to determine culturing capacity and the standard plan of the aquarium are proposed. The water of the aquarium contains much nitrate and phosphate which make the water acidic, but other elements of metabolites are scanty in quantity and innocuous to fish. So the necessary conditions in which fish are cultured healthy and normally are as follows: (1) When M indicates dissolved oxygen, carbon-dioxide, ammonia and dissolved organic matter at t, necessary conditions which enable the culturing for a short time are dM/dt=0. If aeration is enough, ammonia may be the index to satisfy these conditions, because it is more nocuous or poisonous and its oxidation is more difficult than organic matter. When nitrogen compounds secreted from fish is F, oxidized ammonia by bacteria is X1 and assimilated nitrogen compounds is X2: From the results of fish culturing experiments dF/dt is 50 mg per day per 100 grams of fish. Ammonia is oxidized by the action of bacteria developed on the filter-sand and this oxidation is monomolecular-autocatalytic reaction. And also its velocity is proportional to the ratio of exchangeable ammonia of the saynd to total ammonia. Experiments with percolating apparatus (Fig. 1) and culturing the fish in the aquarium show that dXi/dt is 0.14 mg. per day per 10 g. of the sand and dXJdt is 0. 07 mg per day. The sand used is 2~5 mm. size of calcite or weathered granite. Therefore to satisfy these conditions 300 g. of filter sand should be used for culturing 10 g. of fish. (2) Necessary conditions which enable the culturing for a long time without changing the water are to keep constant alkalinity and hydrogen ion concentration. Some metabolites of cultured fish are stocked in the water as nitrate and phosphate which precipitates with calcium or magnesium. As calcium and magnesium ions are eliminated from the water, it loses excess bases and become acidic. This makes the fish unable to live and supresses the ammonia oxidation by bacteria. So the water of the aquarium has need to neutralize the acidity to satisfy these conditions. From these experimental results the standard plan of the aquarium by closed-circulating system is proposed as shown in Table 9. And 60 times of the ratio of exchangeable ammonia of the sand to total ammonia give the culturing capacity of the aquarium by grams of fish per litre. To keep the water in a good condition for the fish, air and calcium-oxide or magnesia should be put in according to the analytical results of pH, dissolved oxygen and alkalinity of the aquarium water. © 1958, The Japanese Society of Fisheries Science. All rights reserved.