96 



Journal of the Kentucky Academy of Science 66(2) 



per body and tail of individual worms to wax 

 in a petri dish, and apply a suction electrode 

 to the transverse band of the cercaria at the 

 junction of the body and the bifurcated tail. 

 White fiber-optic 8.0-mm light cables were 

 covered with the aforementioned filters and 

 adjusted to deliver an intensity of 11.5 fc for 

 each color. An AC amplifier at 10 Hz was 

 used to amplify signals. The average (10 rep- 

 licates) duration of electrical burst activity un- 

 der each light condition was recorded. A one- 

 way, repeated-measures ANOVA was used to 

 compare (1) the mean swimming burst dis- 

 tance and electrical burst activity in the pres- 

 ence of the four red-light treatments and (2) 

 the mean of the four red-light treatments to 

 the individual means of the blue, white, and 

 green regimens. Paired Student's r-tests were 

 used to determine possible differences be- 

 tween each pair of conditions in the latter 

 analysis. 



RESULTS 



The osmolalities of North Elkhorn water 

 and snail extract were determined to be 10- 

 15 and 157 mOsm, respectively. The former 

 closely approximated APW (15 mOsm), while 

 the latter was between ASW (102 mOsm) and 

 ASW supplemented with the 100 mM man- 

 nitol (180 mOsm). Observation of cercariae 

 from the test solutions with a dissecting mi- 

 croscope at 12 hr PE revealed significant 

 swelling and shrinkage of the tail in the 0 and 

 267 mOsm solutions, respectively. Swimming 

 burst distances of cercariae in the five tested 

 osmolalities over 12 hr PE are summarized in 

 Figure 1 . One-way ANOVA analysis revealed 

 significant differences between the mean 

 swimming distances at both 6 (F = 10.064; 

 df = 4, 20; P < 0.001) and 12 hr PE (F = 

 6.622; df = 4, 20; P < 0.001). Swimming of 

 cercariae in APW and ASW remained rela- 

 tively unaffected, with a small decrease at the 

 termination of the experiment (Figure 1). Cer- 

 cariae in 267 mOsm ceased swimming after 

 only 4 hr, while markedly reduced swimming 

 was obvious in distilled water and 180 mOsm 

 (Figure 1). All cercarial bodies placed in the 

 pH 2.0 solution successfully emerged from 

 their tails at 6 hr PE, while 97% emerged after 

 12 hr PE. The lone exception occurred in the 

 267 mOsm solution, where six out of seven 

 bodies emerged. 



Most cercariae remained motionless on the 

 bottom of the cylinder when exposed to white, 

 blue, or green light at the beginning of the 2- 

 min acclimation (i.e., non-recording) period of 

 our light experiment. Conversely, cercariae 

 swam several extended bursts during this ac- 

 climation period when first exposed to red 

 light. No significant differences were ob- 

 served in the mean swimming distances (F 

 0.107; df = 3, 66; P = 0.956; Figure 2a) or 

 electrical burst activity (F = 1.172; df =; 3, 

 27; P = 0.339; Figure 2b) between the four 

 red-light treatments. Mean swimming distanc- 

 es (F = 28.176; df = 3, 66; P < 0.001; Figure 

 2a) and electrical burst activity (F = 9.664; df 

 = 3, 27; P < 0.001; Figure 2b) were signifi- 

 cantly greater under the red-light treatment 

 compared to the blue, white, and green con- 

 ditions. Swimming distances and electrical 

 burst activity were not significantly different 

 when the blue, white, and green conditions 

 were compared to each other, the lone excep- 

 tion being the blue vs. white treatment in the 

 electrical activity analysis (Table 1); all three 

 were significantly different when individually 

 compared to red light (Table 1). 



DISCUSSION 



In our experiments, osmolalities lower than 

 15 mOsm and higher than 102 mOsm signif- 

 icantly affected the vertical swimming dis- 

 tance of the cercaria of P. macrostoma. These 

 results suggested that the continuity of the 

 protective basal membrane identified in the 

 study of Braham and Uglem (2000) became 

 compromised in the more extreme hypotonic 

 and hypertonic solutions. This was visually 

 corroborated by the swelling and shrinkage of 

 cercarial tails from the 0 and 267 mOsm so- 

 lutions at 12 hr PE, respectively. Thus, the 

 plasticity of this tail barrier seems limited to 

 the range of osmolalities (e.g., North Elkhorn 

 Creek water and snail fluid; 15-157 mOsm) 

 these cercariae encounter in nature. None of 

 the tested osmolalities inhibited the activation 

 and subsequent emergence of the P. macros- 

 toma cercarial body from its tail. However, as 

 the conspicuous swimming of the tail serves 

 to attract appropriate centrarchid fish hosts, its 

 loss of function negates the continued viabil- 

 ity/infectivity of the cercarial body. 



Our results indicated that cercarial swim- 

 ming and electrical activity in the tail of the 



