Fish Hatchery Management - fisheries & aquaculture

270 FISH HATCHERY MANAGEMENTin the presence of sunlight and high temperatures and thus are less likelyto be effective during summer months than during the cooler months of theyear. Mixingchemicals may enhance or intensify the toxicity of one ofthem. Also, certain chemicals are toxic to plants and can cause an oxygendepletion if used in ponds at the wrong time.(4) Disease. Although disease may be a self-evident factor, it is disregardedwidely, much to the regret of many fish culturists. Most of the chemicalsused to treat fish diseases are expensive and generally are effectiveonly against certain groups of organisms. Use of the wrong chemical ordrug usually means that several days to a week may pass before one realizesthe treatment was not effective. During this time, large numbers of fishmay be lost unnecessarily.When it is apparent that a treatment is necessary, the following rulesmust be adherred to:(A) Pretreatment Rulesl. Clean holding unit.2. Accurately determine the water volume and flow rate.3. Choose the correct chemical and double-check concentration figures.4. Prevent leaks in the holding unit if a prolonged dip treatment isinvolved (see below).5. Have aeration devices ready for use if needed.6. Make sure of the route by which chemical solutions are dischargedfrom the holding unit.(B) Treatment Rulesl. Dilute the chemical with water before applying it.2. Make sure the chemical is well-mixed in the units or ponds.3. Keep a close watch on units during treatment period.4. Observe fish closely and frequently during treatment (aeration ofwater may be required).5. Turn on fresh water immediately if fish become distressed.(C) Post Treatment Rulesl. Recheck fish to determine success of treatment.2. Do not stress treated fish for at least 48 hours.Various methods of treatment and drug application have been used inthe control of fish diseases. There is no one specific method that is betterthan others; rather, the method of treatment should be based on the specificsituation encountered.DIP TREATMENTDuring the dip treatments, small numbers of fish are placed in a net anddipped in a strong solution of chemical for a short time' usually 15-45