>-#■ 



»*^^ 



mm 



Figure l. — Four sexually mature Myzobdel I a lugubns in the oral cavity of chiselmouth collected in the central Columbia River. The 

 small subterminal mouth of the host is bordered by a cartilaginous upper and lower lip for grazing on sessile algae. The leeches occupy 

 most of the available space in the oral cavity when the mouth is closed. 



Table 2. — Incidence of infestation of chiselmouth and northern 

 squawfish by the piscicolid leech, Myzohdel la luguhris, indicated 

 by infestation ratio.' 



'Infestation ratio = number of fish infested/number of fish examined. 

 ^Numerous small leeches, recently hatched, were attached to some hosts. 



According to Sawyer etal. ( 1975), M. lugubris is 

 a relatively warm-water species encountered most 

 often at 21°-30°C, occasionally at 16°-20°C, and 

 less often in colder water. They reported that the 

 leech appeared to be injured if the water was sud- 

 denly cooled to 10°-15°C in laboratory experi- 

 ments. Obviously some M. lugubris survive over 

 winter at low temperatures, but it must remain 

 inconspicuous due to dormancy in temperate re- 

 gions of North America. We have never recovered 

 M. lugubris during winter in the central Columbia 

 River, either from fish or from benthic samples 



928 



