490 FISH HATCHERY MANAGEMENT 



Ocean Ranching Type of aquaculture involving the release of juvenile 

 aquatic animals into marine waters to grow on natural foods to har- 

 vestable size. 



Open-Formula Feed A diet in which all the ingredients and their pro- 

 portions are public (nonproprietary). 



Operculum A bony flap-like protective gill covering. 



Optic Referring to the eye. 



Osmoregulation The process by which organisms maintain stable 

 osmotic pressures in their blood, tissues, and cells in the face of differ- 

 ing chemical properties among tissues and cells, and between the 

 organism and the external environments. 



Osmosis The diffusion of liquid that takes place through a semiperme- 

 able membrane between solutions starting at different osmotic pres- 

 sures, and that tends to equalize those pressures. Water always will 

 move toward the more concentrated solution, regardless of the sub- 

 stances dissolved, until the concentration of dissolved particles is 

 equalized, regardless of electric charge. 



Osmotic Pressure The pressure needed to prevent water from flowing 

 into a more concentrated solution from a less concentrated one across 

 a semipermeable membrane. 



Outfall Wastewater at its point of effluence or its entry into a river or 

 other body of water. 



Ovarian Fluid Fluid surrounding eggs inside the female's body. 



Ovaries The female reproductive organs. 



Overt Disease A disease, not necessarily infectious, that is apparent or 

 obvious by gross inspection; a disease exhibiting clinical signs. 



Oviduct The tube that carries eggs from the ovary to the exterior. 



Oviparous Producing eggs that are fertilized, develop, and hatch out- 

 side the female body. 



Ovoviviparous Producing eggs, usually with much yolk, that are fertil- 

 ized internally. Little or no nourishment is furnished by the mother 

 during development; hatching may occur before or after expulsion. 



Ovulate Process of producing mature eggs capable of being fertilized. 



Ovum (plural: Ova) Egg cell or single egg. 



Oxidation Combination with oxygen; removal of electrons to increase 

 positive charge. 



Oxytetracycline (Terramycin) One of the tetracycline antibiotics pro- 

 duced by Streptomyces rimosus and effective against a wide variety of 

 bacteria pathogenic to fishes. 



Pancreas The organ that functions as both an endocrine gland secreting 

 insulin and an exocrine gland secreting digestive enzymes. 



