GLOSSARY 501 



Water Hardening Process by which an egg absorbs water that accumu- 

 lates in the perivitelline space. 



Water Quality As it relates to fish nutrition, involves dissolved mineral 

 needs of fishes inhabiting that water (ionic strength). 



Water Treatment Primary: removal of a substantial amount of 

 suspended matter, but little or no removal of colloidal and dissolved 

 matter. Secondary: biological treatment methods (for example, by 

 contact stabilization, extended aeration). Tertiary (advanced): 

 removal of chemicals and dissolved solids. 



Weir A structure for measuring water flow. 



Western Gill Disease See Nutritional Gill Disease. 



Whirling Disease A disease of trout caused by the sporozoan protozoan 

 Myxosoma cere bra lis. 



White Grub An infestation by the metacercarcial stage of Neodiplos- 

 tomum multicellulata in the liver of many freshwater fishes. 



White Spot Disease A noninfectious malady of incubating eggs or on 

 the yolk sac of alevins. The cause of the disease is thought to be 

 mechanical damage. Also see Ich. 



Yellow Grub An infestation by the metacercarial stage of Clinostomum 



marginatum. 

 Yolk The food part of an egg. 



Zooplankton Minute animals in water, chiefly rotifers and crustaceans, 

 that depend upon water movement to carry them about, having only 

 weak capabilities for movement. They are important prey for young 

 fish. 



Zoospores Motile spores of fungi. 



Zygote Cell formed by the union of two gametes, and the individual 

 developing from this cell. 



