Gill-Cleaning Mechanisms of the Crayfish Procambarus clarkii (Astacidea: Cambaridae): Experimental Testing of Setobranch Function

Abstract

Gills of the crayfish Procambarus clarkii are cleaned by two sets of setae which are thrust back and forth among gill filaments by feeding, locomotory, or other movements of thoracic legs. Setae with a complex, rasping microstructure arise from papillae (setobranchs) on the third maxillipeds and pereopods 1-4, and extend up between the inner layer of arthrobranch and outer layer of podobranch gills. The lateral sides of the podobranchs, beyond the range of the setobranch setae, are penetrated by a field of setae projecting from the inner side of the gill cover. These branchiostegal setae bear digitate scale setules like those borne by the setobranch setae. Although cleaning setae act concomitantly with any type of leg movement, these animals engage in a previously unreported behavior, limb rocking, whose sole function appears to be gill cleaning. The effectiveness of cleaning setae was tested with experiments in which setobranch setae were removed from the branchial chamber of one side but not the other. Treated crayfishes set out in commercial ponds and a natural swamp habitat suffered heavy particulate fouling on gill filaments deprived of setobranch setae. The pattern of fouling showed that branchiostegal setae also prevented particulate fouling. However, gill-cleaning setae were not effective against bacterial or ciliate fouling. It is concluded that molting is the only escape from epibiotic fouling