GLOSSARY 497 



Spermatozoon A male reproductive cell, consisting usually of head, 



middle piece, and locomotory flagellum. 

 Spinal Cord The cylindrical structure within the spinal canal, a part of 



the central nervous system. 

 Spines Unsegmented rays, commonly hard and pointed. 

 Spiny Rays Stiff or noncross-striated fin rays. 



Spleen The site of red blood cell, thrombocyte, lymphocyte, and granu- 

 locyte production. 

 Sporadic Disease A disease that occurs only occasionally and usually as 



a single case. 

 Stabilization Pond A simple waste-water treatment facility in which 



organic matter is oxidized and stabilized (converted to inert residue). 

 Standard Length The distance from the most anterior portion of the 



body to the junction of the caudal peduncle and anal fin. 

 Standard Metabolic Rate The metabolic rate of poikilothermic animals 



under conditions of minimum activity, measured per unit time and 



body weight at a particular temperature. Close to basal metabolic rate, 



but animals rarely are at complete rest. See Basal Metabolism. 

 Sterilant An agent that kills all microorganisms. 

 Sterilize To destroy all microorganisms and their spores in or about an 



object. 

 Stock Group of fish that share a common environment and gene pool. 

 Stomach The expansion of the alimentary tract between the esophagous 



and the pyloric valve. 

 Strains Group of fish with presumed common ancestry. 

 Stress A state manifested by a syndrome or bodily change caused by some 



force, condition, or circumstance (i.e., by a stressor) in or on an organism 



or on one of its physiological or anatomical systems. Any condition that 



forces an organism to expend more energy to maintain stability. 

 Stressor Any stimulus, or succession of stimuli, that tends to disrupt the 



normal stability of an animal. 

 Subacute Not lethal; between acute and chronic. 

 Sulfadimethoxine Sulfonamide drug effective against certain bacterial 



pathogens of fishes. 

 Sulfaguanidine Sulfonamide drug used in combination with sulfamera- 



zine to control certain bacterial pathogens of fishes. 

 Sulfamerazine Sulfonamide drug effective against certain bacterial 



pathogens of fish. 

 Sulfamethazine (Sulmet) Sulfonamide drug effective against certain 



bacterial pathogens of fishes. 

 Sulfate Any salt of sulfuric acid; any salt containing the radical SOf. 

 Sulfisoxasole (Gantrisin) Sulfonamide drug effective against certain 



bacterial pathogens of fishes. 



