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For small hatcheries, it may be difficult to manage inbreeding but they should be encouraged to do so. Ifhatcheries maintain a constant Ne = 50 for 5 generations, they will keep F ≤5%. This recommendation producesgood short term (5 generations) management and is not excessive.Techniques to improve Ne include:• Increase number of brood stock that can spawn and provide viable offspringGenetic drift• Keep male: female ration as close to 1:1 as much as possible.• Apply pedigree mating: each male leaves a son and each females leave a daughter as brood stock forfollowing generation (can be more than one but as long as all leave the same number).• Number of offspring used for potential brood stock should be equal among families.• Milt should not be pooled or added in a sequential manner. These practices cause gametic competition andone male can fertilise most of the eggs, producing N e much less than expected.• Stretch the time of replacing brood stock: The desired N e shown in Figure 2 is given in number of generations,not number of years. If the goal is to keep inbreeding below a given value for 20 years and the normalprocedure is to use a 2-year generation interval, 10 generations will be produced during the 20-year plan. But ifgeneration interval could be stretched to 3 years, could be 7 generations would be produced during the 20years, which means a smaller N e could be used to achieve the desired goal.• Procure new brood stock from a different source. If 10-15% new brood stock are introduced each generation,the amount of inbreeding can be drastically reduced.• Maintain two unrelated populations and produce hybrids (or swapping brood stock with other hatcheries).Genetic drift is the random changes in gene frequency – changes that are not due to selection, migration ormutation. The causes can be natural e.g. a sudden raise of temperature due to fire at one stretch of the river thatkills a large number of fish, or could be anthropogenic causes such as the way fish are collected as foundationpopulation.Genetic drift will ultimately lead to the loss of genetic diversity. When procuring fish for broodstock for example,often only a small portion of a population is collected that causes a condition called founder effect – where geneticdrift creates a population in which the gene frequencies are markedly different from those of the originalpopulation.Similar to inbreeding, genetic drift is inversely related to Ne – the smaller Ne the more chance that genetic driftchanges the allele frequencies (i.e. one genetic form will be gradually lost). The probability of losing an allele viagenetic drift in a single population is illustrated in Figure 3.Recommended N e to minimise genetic drift range from 500-5,000 with 500 being the most common. Methods todetermine based on percent guarantee and allele frequencies can be illustrated in Example 2.Example 2: You want to save alleles (frequency q = 0.01) and 95% guarantee of saving the allele (P=0.05) after10 generations. What constant Ne is needed to achieve this goal?• Step 1: Calculate guarantee per generation (G) that is needed to produce a guarantee after 10 generationso 0.95 = G 1040