Dr. Murai Éva szerk.: Parasitologia Hungarica 11. (Budapest, 1978)
mer, and in two groups each in the autumn. Experimental and control fry were exterminated simultaneously after the last feed intake in each test series. The gut was removed from the dissected fishes, ligated at both ends, 0. 5 ml distilled water was injected into it (the mean wet weight of the gut was 0. 5 g). Ten min. later the rinsing fluid was recovered by syringe, and was centrifuged at 19 500 g for 30 min. The supernatant was used for enzyme assays. The guts were homogenated in 10 volumes of distilled water, and the homogenates were centrifuged at 19 500 g for 60 min at +5°C. The supernatant was collected for further study. The same procedure was employed for preparation of extracts from adult tapeworms. Trypsin activity was determined on N- oc-benzoyl-arginine-ethyl ester (BAEE) substrate, as proposed by SCHWERT and TAKENAKA (1955), chymotrypsin activity on N-benzoyl-L-tyrosine-ethyl ester (BTEE) substrate, according to the method of HUMMEL (1959), in a system described in detail in a previous publication (MATSKÁSI and JUHÁSZ, 1977). Unit protease activity was defined as the hydrolytic activity producing increase of the optical density (OD) by 1 000 OD unit in one min, at 253 and 256 nm on BAEE and BTEE substrate, respectively. Enzyme activity differences between the infected and non-infected groups were evaluated by STUDENT'S "t" test. The variation coefficient was determined for 20 routine measurements in each series, to assess reproducibility; the values of 11.8 and 15% were obtained for trypsin and chymotrypsin activities, respectively. The trypsin and chymotrypsin activities determined in the intestinal washing fluids of carp fry infected and not infected with Bothriocephalus acheilognathi are shown in Table 1. Despite considerable individual variations, the group average for trypsin activity was lower in each infected group relative to that found in the controls. Chymotrypsin activity fell significantly below the control level in the fry tested in April and October while in those tested in August and November the probability level was above 5%, although there was a demonstrable activity decrease relative to the control in both instances. TaDle 2 Effect of worm extract on the proteases of fish gut (U/ml) Gut washing fluid Gut washing fluid +worm extract Significance P BAEE-splitting activity (trypsin) x SD n x SD n <^ 0.001 BAEE-splitting activity (trypsin) 2.72 0.46 10 0.21* 0.13 10 <^ 0.001 BTEE-splitting activity (chymotrypsin) 2.09 0.31 10 0.14 0.09 10 <^ 0.001 The activity was determined after 5-minute preincubation. f The activity was determined after 15-minute preincubation. Data on the influence of tapeworm extract on the trypsin and chymotrypsin activities of intestinal washing fluid are shown in Table 2. In this series, activity determinations were carried out in the following system: 2.3 ml 0.1 M Tris HCl buffer (pH 7. 4), with 8 mM CaClg added +0.5 ml substrate +0.1 ml intestinal washing fluid +0.1 ml parasite extract. The determinations were carried out on the gut-washing fluid of the non-infected fry, collected in April.
