BIOELECTRONIC MONITORING OF PARASITE-INDUCED STRESS IN BROWN TROUT AND ROACH

A non-contact bioelectronic monitoring system was used to record chang es in heart rate, ventilation rate and swimming activity in brown trou t Salmo trutta and roach Rutilus rutilus, following exposure to two sp ecies of cercariae of digenean trematodes: Diplostomum pseudospathaceu m which is a common parasite in the lens of fishes and xiphidiocercari ae of Plagiorchis elegans, a parasite of anatid birds, both of which h ave the snail Lymnaea stagnalis as their first intermediate host. Swim ming activity increased significantly in roach exposed to Diplostomum cercariae at densities as low as 3.81(-1) and remained elevated for 24 -36 h post exposure. Brown trout showed no response when exposed to lo w densities of Diplostomum (2.9 and 5.7 cercariae 1(-1)) but there was a significant response at higher cercarial exposure densities (>50 1( -1)). Total activity of brown trout increased immediately, peaking aft er 2 h and returning to pre-exposure levels within 5-6 h. There was a simultaneous increase in heart and ventilation rates which both declin ed following the reduction in activity of the fish. Heart rate then in creased for a second time to a maximum level at 14-16 h and thereafter declined to reach a steady state at 3 days post-exposure. During this period there was no significant change in total activity. The qualita tive nature of the heart response was identical in five infected brown trout although the magnitude of the response varied widely among fish . Exposure to cercariae of P. elegans elicited no response in either f ish species. (C) 1996 The Fisheries Society of the British Isles