PARTICLE CLEARANCE FROM THE GILLS OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The rate of particle clearance from the gills was assessed in healthy rainbow trout (Oncorhynchus mykiss), challenged with the formalin-kill ed bacterium Flavobacterium branchiophilum, as well as in fish with al tered ventilation levels produced by varing the concentrations of diss olved oxygen (DO) in the water. The clearance of F. branchiophilum fro m the gills was quantified by means of an enzyme-linked immunosorbent assay. Fish held under normoxic conditions (DO = 9.5 mg/l) showed an i nitial rapid reduction in bacterial antigen, with 50% of the bacteria being cleared in the first 12 h after exposure, followed by slower cle arance for the remaining bacteria; total elimination was achieved by 4 0 h. Fish with reduced ventilation rates (hyperoxia; DO = 25mg/l) and elevated ventilation rates (hypoxia; DO = 4.5 mg/l) had significantly impaired particle clearance (r<0.05), achieving only 60 and 20% reduct ion, respectively, at 72 h after challenge. (C) 1998 W.B. Saunders Com pany Limited.