High apostome ciliate endoparasite infection rates found in the Bering Sea euphausiid Thysanoessa inermis

Abstract

Samples of the Bering Sea euphaustiid Thysanoessa inermis (Kroyer), collected at 2 stations in the Bering Sea and consisting primarily of first-year adult females and last-furcilia-stage sub-adults, were studied to determine the percentage infected by the apostome ciliate endoparasite Collinia beringensis (Capriulo & Small). In both groups of krill, infection percentage was found to be extremely high, at 98 and 68% respectively. The higher rate of 98% was found in the sample composed of larger and older euphausiids. Such infestation rates suggest that these ciliates may be important modifiers of euphausiid production.