Fish Hatchery Management - fisheries & aquaculture

IOFISII HAI.CHERY MANAGEMENl.resistant to high levels of carbon dioxide but 50(l; mortality can occurwhen carbon dioxide concentrations reach 90 parts per million. However,concentrations of 40 ppm carbon dioxide have little affect upon juvenilecoho salmon.TOXIC GASESHydrogen sulfide (UrS) and hydrogen cyanide (HCN) in very low concentrationscan kill fish. Hydrogen sulfide derives mainly from anaerobicdecomposition of sulfur compounds in sediments; a few parts per billionare lethal. Hydrogen cyanide is a contaminant from several industrialprocesses, and is toxic at concentrations of 0.1 part per million or less.DISSOLVED GAS CRI'fE,RIAAs implied above, various fish species have differing tolerances to dissolvedgases. However, the following general guidelines summarize water qualityfeatures that will support good growth and survival of most or all fishspecres:OxygenNitrogenCarbon dioxideHydrogen sulfideHydrogen cyanide5 parts per million or greater100(ll saturation or less10 parts per million or less0.1 part per billion or lessl0 parts per billion or lessIn general, oxygen concentrations should be near 100(li, saturation in theincoming water supply to a hatchery. A continual concentration of 80'li, ormore of saturation provides a desirable oxygen supply.Suspended and Dissolaed Solids.,Solids"in water Ieave tangible residues when the water is filtered(suspended solids) or evaporated to dryness (dissolved solids). Suspendedsolids make water cloudy or oPaque; they include chemical precipitates,flocculated organic matter, living and dead planktonic organisms, and sedimentstirred up from the bottom on a pond, stream, or raceway. Dissolvedsolids may color the water, but leave it clear and transParent; they includeanything in true solution.SUSP!]NDED SOI,IDS,,Turbidity"is the term associated with the presence of suspended solids.Analytically, turbidity refers to the penetration of light through water (the