Optimum Food Consumption Rate of L-Type Rotifer Brachionus plicatilis in Culture on the Basis of the Growth Rate and water Quality Maintenance

Abstract

Optimum food consumption rate, which maintains lower pollution of culture water and higher growth rate of rotifer, was estimated on the basis of food energy distribution and water quality. Immediate dissolved oxygen demand (IDOD) was used as an indicator of the water quality.
In the first experiment, rates of food consumption and growth were determined. Five aqualia with different density levels of marine Chlorella sp.; 0.5, 1, 3, 5, and 8×10⁶ cells/ml, were prepared and maintained at the particular density by periodical addition of concentrated algae. Rotifers were inoculated at the density of 50ind/ml. In order to maintain the selected density, rotifers were harvested every morning. At the same time, 30% of the culture medium was changed. The rate of aeration was 400ml/min. Water temperature, salinity, pH and light were adjusted at 20±1°C, 20‰, 7.5 and 100lx (15L: 9D), respectively. The experimental period was 2 weeks with an acclimation time of 4 days.
In the second experiment, oxygen consumption rate of rotifer and IDOD were determined at each of the previously determined food densities. A respirometer of automated type was used for the measurement. The duration of each recording cycle for the culture medium with and without rotifer was 30 min. IDOD was calculated by subtracting physico-chemical oxygen consumption of the DO probe, rubber stopper, and surface of the chamber from the recorded DO value. Each group of rotifers was cultured in a 5l conical tank, under the same environmental condition as that of the first experiment. Rotifers were acclimated to the experimental conditions for 4 days. After changing the culture medium with filtered sea water, DO was recorded for 24h.
IDOD values related to culture age increased linearly with the regressive gradients being steeper at densities above 3×10⁶ cells/ml. The growth rate of rotifer increased rapidly within the food densities between 0.5 and 3×10⁶ cells/ml and became constant at higher densities. Energy loss values showed the same tendency as the growth rate. On the other hand, food conversion rate increased up to 3×10⁶ cells/ml but decreased rapidly at higher algal densities. It can be deduced that above this density (3×10⁶ cells/ml) water becomes polluted faster, due to an increase in energy loss. The optimum food consumption rate for L-type rotifer was estimated to be around 357% of the body dry-weight per day at the food density of 3×10⁶ cells/ml. This value corresponds to about 70% of the saturated rate of food consumption.