494 FISH HATCHERY MANAGEMENT 



Random Mating Matings without consideration of definable charac- 

 teristics of the broodfish; nonselective mating. 



Ration A fixed allowance of food for a day or other unit of time. 



Ray A supporting rod for a fin. There are two kinds: hard (spines) and 

 soft rays. 



Rearing Unit Any facility in which fish are held during the rearing 

 process, such as rectangular raceways, circular ponds, circulation race- 

 ways, and earth ponds. 



Recessive Character possessed by one parent that is masked in the 

 progeny by the corresponding alternative or dominant character 

 derived from the other parent. 



Reciprocal Mating (Crosses) Paired crosses in which both males and 

 females of one parental line are mated with the other parental line. 



Reconditioning Treatment Treatment of water to allow its reuse for 

 fish rearing. 



Rectum Most distal part of the intestine; repository for the feces. 



Red Pest See Motile Aeromonas Disease. 



Red Sore Disease See Vibriosis. 



Redd Area of stream or lake bottom excavated by a female salmonid 

 during spawning. 



Redmouth Disease An original name for bacterial hemorrhagic septicemia 

 caused by an infection of Aeromonas hydrophila specifically. Synonyms: 

 motile aeromonas disease; bacterial hemorrhagic septicemia. 



Residue, Tissue Quantity of a drug or other chemical remaining in 

 body tissues after treatment or exposure is stopped. 



Resistance The natural ability of an organism to withstand the effects 

 of various physical, chemical, and biological agents that potentially are 

 harmful to the organism. 



Resistant, Drug Said of a microorganism, usually a bacterium, that can- 

 not be controlled (inhibited) or killed by a drug. 



Reuse, Recycle The use of water more than one time for fish propaga- 

 tion. There may or may not be water treatment between uses and dif- 

 ferent rearing units may be involved. 



Riboflavin An essential vitamin of the B-complex group (B2). 



Roccal See Quaternary Ammonium Compounds. 



Roe The eggs of fishes. 



Roundworm See Nematoda. 



Sac Fry A fish with an external yolk sac. 



Safe Concentration The maximum concentration of a material that 



produces no adverse sublethal or chronic effect. 

 Salinity Concentration of sodium, potassium, magnesium, calcium, 



