104 



Journal of the Kentucky Academy of Science 66(2) 



4 

 3.5 



3 



ui 2.5 

 (/> 



+1 2 

 c 



(0 

 V 



S 1.5 

 1 



0.5 



□ 15-Day Experiment 

 B20-Day Experiment 



Adult Worm Types 



Figure 3. Mean ± SE of Type I and Type II (N = 23 

 worms; 15-day experiment) and Type 1 — III (N = 110 

 worms; 20-day experiment) Proterometra macrostoma 

 adults from experimental infections of bluegill. An indi- 

 vidual fish was exposed to three cercariae at one or two 

 weekly intervals resulting in 8- and 15-day infections or 

 6-, 13-, and 20-day infections, respectively. 



recovered in our 15 -day experiment (Figure 

 3). Similarly, a one-way ANOVA showed no 

 significant difference (F = 1.607; df = 2, 39; 

 sig, = 0.213) in the mean number of Type I 

 (N = 42), II (N = 35), or III (N = 33) adults 

 recovered in our 20-day experiment (Figure 

 3). The 8- and 15-day old worms in the 15- 

 day experiment were likely represented by the 

 Type I and II worms, respectively, based on 

 the previous work of Rosen et al. (2000). Sim- 

 ilarly, the 6-, 13-, and 20-day old worms in 

 the 20-day experiment represented the Type I, 

 Type II, and Type III worms, respectively 

 (Rosen et al. 2000). Egg number increased 

 and different egg developmental stages be- 

 came apparent in the older experimental in- 

 fections in our 20-day study (Figure 4). 



No mortality or gradual progression of host 

 pathology was noted in our timed (i.e., 7-, 14-, 

 and 24-day) infections, and damage appeared 

 to be restricted to the immediate area of worm 

 attachment to the host mucosa. At the host- 

 parasite interface, the fish mucosa was char- 

 acterized by small lesions, and the mucosa 

 and submucosa were constricted by the 

 worm's oral sucker (Figure 5a). There was ob- 

 vious epithelial necrosis and hemorrhaging at 

 this attachment site (Figure 5b). Serial sec- 

 tions revealed complete detachment of host 

 tissue (Figure 5c) undergoing advanced necro- 

 sis (Figure 5d) in the oral suckers of many 

 worms. Notably, no experimentally infected 



2 



oi 

 o> 

 IJJ 



ui 40 

 <n 



+1 30 



□ stage I Eggs 



□ stage II Eggs 

 □Stage III Eggs 



I II III 



Adult Worm Types 



Figure 4. Mean ± SE of egg stages found in Type I to 

 III Proterometra macrostoma adults recovered from ex- 

 perimental infections of 14 bluegill. 



fish died before they were sacrificed at the end 

 of this study. 



DISCUSSION 



As predicted, based on this time frame for 

 egg development (Rosen et al. 2000), it was 

 possible to create an equal mix of P. macro- 

 sotma Type I and II and Type I to III adult 

 worms in our 15- and 20-day laboratory ex- 

 periments, respectively. This was accom- 

 plished by exposing a particular fish to equal 

 numbers of cercariae at one or two weekly 

 intervals. In natural infections, the proportions 

 of these worm types within a host would thus 

 provide an accurate measure of new infections 

 with P. macrostoma. 



Williams and Jones (1994) indicated that 

 one of the most important factors affecting in- 

 fection of hosts with parasitic worms is en- 

 vironmental temperature. Seasonal recruit- 

 ment of trematodes lacking a metacercarial 

 stage is clearly linked to such temperature 

 changes. Several long-term studies with schis- 

 tosomes have shown that maturation of cer- 

 cariae within snails may slow or stop at low 

 temperatures and that emergence itself may be 

 inhibited (Schiff et al. 1975; Sinderman 

 1960). Lewis (1988) reported that P. macros- 

 toma cercariae will not emerge from snails un- 

 less water temperature reaches 15°C, and Ug- 

 lem (1980) recorded water temperatures at 

 North Elkhom Creek above 15°C only be- 

 tween March and October. Notably, Riley and 

 Uglem (1995) observed no laboratory emer- 

 gence of this species between October and 



