Fish Hatchery Management - fisheries & aquaculture

AppendixChemical Treatments:Calculations and ConstantFlow DeliveryHatchery systems often receive prolonged-bath or constant-flow chemicaltreatments that adjust water quality or control diseases. In prolonged-bathtreatments (without water flow), chemicals are,spread over the surface ofthe water body, and mixed throughout its volume, by hand or machine.Many hatchery tanks and most ponds, particularly large ones, are treatedstatically. In constant-flow treatments, chemicals are metered at one pointinto continously renewed water supplies; the turbulence of the movingwater accomplishes the mixing. Constant-flow treatments typically are usedin intensive culture when even a temporary halt in the supply of freshwater might cause fish mortality because of oxygen depletion or wasteaccumulation.Chemical applications normally are couched in terms of final concentrations;a pond treatment of 2 parts per million rotenone means the wholepond should contain this concentration after application. Concentrations,in turn, typically are weight ratios: weight of chemical in solution (orsuspension) per weight of solvent (usually water). The ratio may beexpressed in terms either of unit solvent weight or of unit solute weight.Ten pounds chemical per ton of water, and one pound chemical per 200pounds water (1:200), both represent the same concentration. Even when aconcentration is expressed in terms of volume or capacity (pounds/acrefoot;milligrams/liter), it is the equivalent weight of that volume of waterthat is implied.401