Fish Hatchery Management - fisheries & aquaculture

FISH HATCHERY MANAGEMENTpossible adverse effects on the pond environment. Some treatment chemicalsare algicidal or herbicidaland may kill enough plants to ultimatelycause an oxygen deficit. Other chemicals, such as formalin, may reducedissolved oxygen levels as they degrade.As in prolonged-bath treatments, it is important that the chemical beevenly distributed throughout the culture unit to prevent the occurrence ofhot spots. Special boats are available for applying chemicals to ponds.However, such chemical boats are fairly expensive and are not needed unlesslarge acreages are involved. For dry chemicals that dissolve rapidly inwater, such as copper sulfate or potassium permanganate, burlap or anycoarse-weave bags can be used. The required amount of chemical is putinto a bag and towed behind the boat so that the chemical dissolves in thewake of the boat. Liquids and wettable powders can be applied evenly withhand or power sprayers or can be siphoned over the edge of a boat into theprop wash.As with the prolonged-bath method, there is no one correct way to applya chemical evenly to the unit of water to be treated. Rather, the applicationwill depend on the kind of chemical being used, the equipment available,and the type of unit to be treated.FLUSH TREATMENTFlush treatments are simple, and consist of adding a solution of the treatmentchemical at the upper end of a holding unit and allowing it to flushthrough. It has been used widely at trout and salmon hatcheries, but is seldomused at warmwater hatcheries. It is applicable only with raceways,tanks, troughs, or incubators for which an adequate flow of water is available,so that the chemical is completely flushed through the unit or systemwithin a predetermined time. Highly toxic chemicals should be avoided becausethere is no way to assure a uniform concentration within the unit beingtreated.CONSTANT-FLOW TREATMENTConstant-flow treatments are useful in raceways, tanks, or troughs in situationswhere it is impractical or impossible to shut off the inflowing waterlong enough to use prolonged baths (Appendix G).The volume of water flowing into the unit must be determined accuratelyand a stock solution of the chemical metered into the inflowing water toobtain the desired concentration. Before the metering device or constantflowsiphon that delivers the chemical is started, enough chemical shouldhave been added to the water in the device to give the desired concentration.Upon completion of the desired treatment period, the inflow of chemicalis stopped and the unit is flushed by allowing the water flow to continue.