[The effect of husbandry shortcomings on oxygen supply in pet fish tanks]

In order to investigate the suitability of standard fish tank setups for permanent keeping of ornamental pet fish, oxygen consumption and exchange rates were measured in a group of standard aquariums with a volume of 54 litres.

The effects of defined disturbances on oxygen partial pressure in fish tanks were measured. These simulated typical beginners' errors such as a high stocking density, excessive feeding, insufficient filter cleaning, lack of water movement, and plant coverage of the water surface. Quantitative changes in oxygen partial pressure were measured in the tank as well as in a simplified model tank.

Oxygen uptake rate of the tank (substrate, aquatic plants, bacteria, reduced substances) was not quantifiable in the experiment. The metabolism of the fish, which increased sharply with the feeding dose, exhibited the greatest effect on oxygen consumption in the fish tank. Oxidative conversion of nitrogen from ammonia to nitrate also caused a decrease in oxygen content, however to a lesser extent. Oxygen uptake from the atmosphere was significantly modulated by water flow rate and size of the diffusion area of the water surface.

These results allow quantitative predictions concerning the interaction of fish stocking density and oxygen balance in standard commercial aquarium setups. Even under conditions of high stocking density, poor filter hygiene and excessive feeding, all tested tanks demon strated their suitability for permanent keeping of ornamental fish. Care is warranted, however, that water flow is maintained and its surface is not covered by plants. Ideally, the fish should be fed several small portions during daytime rather than a single large ration.