Journal of crustacean biology vol:13 pages:245-255
The relationships of filtration and ingestion rates at different food concentrations were analyzed in individuals of different sizes in the fairy shrimp Streptocephalus proboscideus and ingestion rate determined in relation to sex, animal density, light and darkness, culture medium, and water quality at one food concentration. Maximum ingestion rates of about 1,000,000 cells animal-1 h-1 in adult males (13-14 mm) were measured for food concentrations between 50,000 and 500,000 algal cells (Selenastrum capricornutum) ml-1. At higher food concentrations, ingestion rates dropped. For the largest size class tested (13.7 mm), maximum ingestion rate (about 820,000 cells animal-1 h-1) was more than 10 times higher than in the smallest size class (4.4 mm) and was reached at a lower cell concentration (about 80,000 cells ml-1) than in the smallest animals (about 280,000 cells ml 1). Significant sexual differences in ingestion rates were observed in SRW (P < 0.05) and EEC (P < 0.01) synthetic fresh-water media for the 12-h measurements and in SRW medium for the 3-h experiments (P < 0.05). These results, however, were not confirmed by a third series of 3-h experiments in SRW medium. Significant influences of culture medium on feeding rates were observed in females only. The ingestion rate in darkness (1,43 5,000 +/- 1,118,000 cells animal-1 h-1) was not significantly different from that in light (1, 120,000 +/- 812,000 cells animal-1 h-1). Increasing the density to more than 10 animals in 500 ml of medium had a negative effect on the feeding rate. High NH3-N and NO2-N concentrations had an inhibitory effect on food uptake; interpolated EC50 values were approximately 4 mg l-1 and 60 mg l-1, respectively.