10 MSH HAICHKRY MANAGEMENT 



resistant to high levels of carbon dioxide but 50'^ mortality can occur 

 when carbon dioxide concentrations reach 90 parts per million. However, 

 concentrations of 40 ppm carbon dioxide have little affect upon juvenile 

 coho salmon. 



TOXIC GASES 



Hydrogen sulfide (H^S) and hydrogen cyanide (HCN) in very low concen- 

 trations can kill fish. Hydrogen sulfide derives mainly from anaerobic 

 decomposition of sulfur compounds in sediments; a few parts per billion 

 are lethal. Hydrogen cyanide is a contaminant from several industrial 

 processes, and is toxic at concentrations of 0.1 part per million or less. 



DISSOLVED GAS CRITERIA 



As implied above, various fish species have differing tolerances to dissolved 

 gases. However, the following general guidelines summarize water quality 

 features that will support good growth and survival of most or all fish 

 species: 



Oxygen 5 parts per million or greater 



Nitrogen 100% saturation or less 



Carbon dioxide 10 parts per million or less 



Hydrogen sulfide 0.1 part per billion or less 



Hydrogen cyanide 10 parts per billion or less 



In general, oxygen concentrations should be near 100"ii saturation in the 

 incoming water supply to a hatchery. A continual concentration of 80"ii or 

 more of saturation provides a desirable oxygen supply. 



Suspended and Dissolved Solids 



"Solids" in water leave tangible residues when the water is filtered 

 (suspended solids) or evaporated to dryness (dissolved solids) Suspended 

 solids make water cloudy or opaque; they include chemical precipitates, 

 flocculated organic matter, living and dead planktonic organisms, and sedi- 

 ment stirred up from the bottom on a pond, stream, or raceway. Dissolved 

 solids may color the water, but leave it clear and transparent; they include 

 anything in true solution. 



SUSPENDED SOLIDS 



"Turbidity" is the term associated with the presence of suspended solids. 

 Analytically, turbidity refers to the penetration of light through water (the 



