Fish Hatchery Management - fisheries & aquaculture

IO4FISH HATCHERY MANAGEMENTthat these fish would compete for space and interfere with the productionof other, more desirable species.Extensive development of herbicides in recent years makes chemical controlof weeds quite promising in many instances. When properly applied,herbicides are effective, fast, relatively inexpensive, and require less laborthan some of the other control methods. Chemical control, however. is not asimple matter. Often the difference in toxicity to weeds and to fish in thepond is not great. Some chemicals are poisonous to humans or to livestockand they may have an adverse effect on essential food organisms. Decay oflarge amounts of dead plants can exhaust the oxygen supply in the water,causing death of fish and other aquatic animals. It is essential that discretionregarding treatment be followed if satisfactory results are to be obtained.An important aspect of vegetation control is the rate of dilution of appliedherbicides and the effect of substances present that may neutralizethe toxicity of the chemical used. The rate of water exchange by seepageor outflow and the chemical characteristics of the water and pond bottomalso affect the success of chemical control measures. Often the herbicidemust reach a high percentage of the plant surface before a kill is obtained;the chemical must be applied carefully if good results are to be achieved.The herbicide is applied directly on emergent or floating weeds and tothe water where submerged weeds are growing. The first type of treatmentis called a local treatment, the second is termed a solution treatment appliedeither to a plot or to the entire pond.Conventional sprayers are used to apply the local treatments and insome instances may be suitable for solution treatments. Chemicals for solutiontreatment are sometimes diluted with water and poured into the wakeof an outboard motor, sprinkled over the surface of the pond, or run bygravity into the water containing the weed beds. Crystalline salts may beplaced in a fine woven cotton bag and towed by boat, allowing the herbicideto dissolve and mix with the pond water. Some herbicides areprepared in granular form for scattering or broadcasting over the areas tobe treated. Generally, the more rapidly the chemical loses its toxicity themore uniformly it must be distributed over the area involved for effectiveresults. Also, if the chemical is at all toxic to fish, it must be uniformly distrib'rted.Emergent or floating vegetation receiving local treatments appliedwith spray equipment should be uniformly covered with a drenching sprayapplied as a fine mist.A number of precautions should always be taken when herbicides areused. Follow all instructions on the label and store chemicals only in theoriginal labeled container. Avoid inhalation of herbicides and prevent theirrepeated or prolonged contact with the skin. Wash thoroughly after handlingherbicides, and always remove contaminated clothing as soon as possible.Prevent livestock from drinking the water during the post-treatmentperiod specified on the label. Do not release treated water to locations that