478 FISH HATCHERY MANAGEMENT 



Dentary Bones The principal or anterior bones of the lower jaw or 



mandible. They usually bear teeth. 

 Depressed Flattened in the vertical direction, as a flounder. 

 Depth of Fish The greatest vertical dimension; usually measured just in 



front of the dorsal fin. 

 Dermal Pertaining to the skin. 



Dermatomycosis Any fungus infection of the skin. 

 Diarrhea Profuse discharge of fluid feces. 

 Diet Food regularly provided and consumed. 

 Dietary Fiber Nondigestible carbohydrate. 



Digestion The hydrolysis of foods in the digestive tract to simple sub- 

 stances that may be absorbed by the body. 

 Diluent A substance used to dissolve and dilute another substance. 

 Dilution Water Refers to the water used to dilute toxicants in aquatic 



toxicity studies. 

 Dip Brief immersion of fish into a concentrated solution of a treatment, 



usually for one minute or less. 

 Diplostomiasis An infection involving larvae of any species of the genus 



Diplostomum, Trematoda. 

 Dipterex See Dylox. 

 Disease Any departure from health; a particular destructive process in 



an organ or organism with a specific cause and symptoms. 

 Disease Agent A physical, chemical, or biological factor that causes 



disease. Synonyms: etiologic agent; pathogenic agent. 

 Disinfectant An agent that destroys infective agents. 

 Disinfection Destruction of pathogenic microorganisms or their toxins. 

 Dissolved Oxygen The amount of elemental oxygen, O2, in solution 



under existing atmospheric pressure and temperature. 

 Dissolved Solids The residue of all dissolved materials when water is 



evaporated to dryness. See Salinity. 

 Distal The remote or extreme end of a structure. 

 Diurnal Relating to daylight; opposite of nocturnal. 

 Dorsal Pertaining to the back. 

 Dorsal Fin The fin on the back or dorsal side, in front of the adipose 



fin if the latter is present. 

 Dose A quantity of medication administered at one time. 

 Drip Treatment See Constant- Flow Treatment. 

 Dropsy See Edema. 



Dry Ration A diet prepared from air-dried ingredients, formed into dis- 

 tinct particles and fed to fish. 

 Dylox (Dipterex, Masoten) Organophosphate insecticide effective in the 



control of parasitic copepods. 

 Dysentery Liquid feces containing blood and mucus. Inflammation of 



the colon. 



