PREDATORY FILTER-FEEDING IN FAIRY SHRIMPS - FUNCTIONAL-RESPONSE OF STREPTOCEPHALUS-PROBOSCIDEUS (CRUSTACEA, ANOSTRACA) FED ANURAEOPSIS-FISSA (ROTIFERA)

Four size classes of both sexes of laboratory-cultured Streptocephalus proboscideus (post-metanauplii 4.7+/-0.4; juvenile virgins 8.7+/-0.7; adults I 13.8 +/- 0.9, and adults II 22.07 +/- 1.1 mm) were fed five concentrations (20 to 320 ml-1) fo Anuraeopsis fissa, or six concentra tions (20 to 640 ml-1) in adults I and adults II, for 30 minutes. Post -metanauplii consumed at maximum 66 +/- 9 rotifers ind.-1 min.-1 (mean +/- S.D.) while the largest adult females maximally ingested 347 +/- 37 rotifers min.-1. Regardless of predator size and sex, prey consumpt ion was dependent on prey density. Functional response curves either p lateaued or declined at 320 prey ml-1 in post-metanauplii, juveniles a nd adults I, and at 640 ml-1 in adults II. Females consumed c. 40% mor e prey than males. On a daily basis, adult II females consumed up to 1 .05 mg rotifer dry weight (10% of their own body weight) while post-me tanauplii consumed up to 0.2 mg DW (100% of their body weight). Interm ediate stages had intermediate consumption rates. Filtration rates ind icated that a fully grown S. proboscideus may filter as much as 2 1 of water per day, suggesting that fairy shrimps, in their natural enviro nment, may often be food-limited.