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Maintaining genetic quality of fish shellfish under small holder farmers in theASEAN countriesThuy T. T. NguyenNetwork of Aquaculture Centres in Asia-Pacific Suraswadi Building,Department of Fisheries Kasetsart University CampusBangkok 10900, ThailandAbstractThis document aims to provide simple concepts and practical methods in genetic management in hatcheries.These include concepts on inbreeding, effective breeding number, genetic drift and bottlenecks and therelationship between them. The ultimate goal of genetic management of broodstock is to reduce inbreeding asmuch as possible and simple and practical methods to address inbreeding issue are discussed.Aquaculture is a critical sector for food production in the ASEAN. As with other farming sectors, aquacultureproduction in the ASEAN is dominated by small scale farms, which are essentially family owned, operated andmanaged.In some of the ASEAN countries, the seed production sector is managed by the government hatcheries (i.e.nucleus) where genetic improvement programs are undertaken, and the seed are broodstock are disseminated toa number of hatcheries (i.e. multipliers) where seed are produced and supplied to farmers. In such a system,genetic quality of the seed are managed at the nucleus level and farmers do not have to worry about geneticmanagement aspects, provided that the genetic management scheme at the nucleus and multipliers levels aresatisfactory.However, it is also true that in many countries small scale hatcheries exist in order to support the aquaculturesector in rural areas. Examples include hatcheries for the Chinese and Indian major carps and tilapia. There isevidence to suggest that genetic quality produced by many hatcheries in the region had deteriorated. Aquaticspecies in general are highly fecund, coupled with the tendency of keeping a small number of brood stocks toreduce production costs would result in a rapid loss of genetic diversity.Genetic changes in hatcheries will not only affect the performance of seed, and hence productivity, but alsoindirectly pose potential impacts on the wild counterparts. Special attention should be paid in the case ofindigenous species where the wild gene pool needs to be conserved.This documents aims to provide some fundamental concepts on genetic management aspects of brood stocks inhatcheries. Genetic management of brood stock involves the control of inbreeding, genetic drift and bottleneck.InbreedingInbreeding is the mating of relatives, for examples between brother and sister, between cousins, or betweenparents and their offspring. Although well planned and directed inbreeding can be beneficial, unintentional andunplanned inbreeding will cause problems.Genetically, inbreeding increases homozygosity in the offspring (i.e. genetic similarity) which means it alsodecreases heterozygosity (i.e. genetic diversity). Homozygosity is also produced when non-relatives mate and37
genetically, the two forms of homozygotes are identical. Even though the two forms of homozygosity are identical,a distinction is made because of the way homozygosity is produced and its consequence.Why inbreeding is a concern? As inbreeding increases, it often causes a decrease in productivity which is termed“inbreeding depression”. Inbreeding depression is a decrease in growth rate, fecundity, appearance of deformities,etc. that is observed in the inbred group when it is compared to a control population where there is no inbreeding.The negative effects of inbreeding usually do not manifest immediately. Inbreeding depression is often delayed(i.e. they may not occur until several generations after inbreeding has begun). How quickly inbreeding depressionoccurs and manifest depends on the amount of inbreeding that has been produced and the trait.However, note that it could be erroneous to think that inbreeding is a major reason behind many of the productionproblems. Deformities and decrease in yield are also due to non-genetic factors such as developmental errors,toxins, nutritional deficiencies and poor water quality.Inbreeding can be avoided by tagging animals so that parent-offspring, brother-sister and half-siblings matings canbe avoided. However, tagging for large number of fish can be expensive for small scale hatcheries, as suchhatcheries must manage the population as a whole to minimise accumulation of inbreeding by managing theeffective breeding number (N e ).N e is determined by:4NfNmN e =Nf+ NmWhere: Nf and Nm are number of females and males that leaves viable offspring which in turn contribute geneticmaterial to the next generation.Based on the above equation, Ne can be increased by two ways:• Increasing number of number of females and males that leaves viable offspring which in turn contribute geneticmaterial to the next generation; and• Bringing sex ratio to 1:1.Example 1:A fish hatchery has 1000 brood stock, of which the managers used 900 brood stock for spawning this year.However, only 800 brood stock produced viable offspring. He uses hand-striping and artificial fertilisationtechnique and keeps viable offspring from all families for potential brood stock.1.Calculate N e in case sex ratio he used was 1:1; (Assuming his brood stock population has 400 males and 400females)2.What N e would be if he used sperm from 1 male to fertilise eggs of 3 females?3.What would happen to N e if assuming case 1, but he sells offspring from 200 families for grow-out farmers, and onlykeeps some offspring of the remaining families for potential brood stock?So what is the relationship between Ne and inbreeding? The reason we need to manage Ne is that it is reverselyrelated to inbreeding:1F =2N e38
Page 1 and 2: Training of TrainersProgramme3-7 Au
Page 3 and 4: Table of Contents1. Preface 42. Sen
Page 5 and 6: knowledge about the activities carr
Page 7 and 8: iosphere, in that it is essentially
Page 10 and 11: Importance in narrowing the supply
Page 12 and 13: Figure 7: The trend in aquaculture
Page 14: aquaculture has been a success thus
Page 17 and 18: pathogen transfer is generally cons
Page 19 and 20: • It highlights the importance a
Page 21 and 22: particular animal are identified, t
Page 23: Knowledge at the bottom of the pyra
Page 26 and 27: farmer innovation process. In this
Page 28 and 29: • Rapport building• Working str
Page 30 and 31: shrimp farming is undertaken in the
Page 32 and 33: Reintjes, C and Hiemstra, W. 1989 F
Page 34 and 35: • An increase in reliable product
Page 36 and 37: Principles of AACC are to: 1) Facil
Page 40 and 41: Where F is the percent increase in
Page 42 and 43: o G=(0.95) 1/10G =0.994883803Figure
Page 44 and 45: Aquaculture extension and training
Page 46 and 47: ResearchExtensionFarmersFlow of inf
Page 48 and 49: view of outside world than before a
Page 50 and 51: Along with fish sample, the support
Page 52 and 53: Fungal examinationFungal infection
Page 54 and 55: few different pathogen strains. The
Page 56 and 57: Major finfish diseases in Asia and
Page 58 and 59: A great number and diversity of ani
Page 60 and 61: • -oxidase test positive• -resi
Page 62 and 63: ReferencesAustin, B. and D. Austin.
Page 64 and 65: Accessing better markets-improving
Page 66 and 67: Owing to its importance in generati
Page 68 and 69: adopt standards for responsible shr
Page 70: Tokrisna R, Benheam W., 1995. Gain
Page 73 and 74: of the temperature rise that were d
Page 75 and 76: Principles of developing, validatin
Page 77 and 78: such as determinants, exposures and
Page 79 and 80: How to promote adoption of BMPs?Pro
Page 81 and 82: economic sustainability. BMPs need
Page 83 and 84: Once you understand your stakeholde
Page 85 and 86: As conventional approaches such as
Page 87 and 88: Printed publicationsPrinted publica
Page 89 and 90:
Set up a blog or website for your w
Page 91 and 92:
If you have a website, all you need
Page 93 and 94:
ought about increased profits among
Page 95 and 96:
• It is a farming system the prod
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Annex 1. The area surveyed for obta
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contribute substantially to maintai
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seawater, but in fresh water its le
Page 103 and 104:
type of ingredients used, since som
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This is a new approach used to buil
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New, M.B., A. G. J. Tacon and I. Cs
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later stages it has become a much m
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c. Improved information exchange an
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implemented by both societies. Inte
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With better informed farmers, the s
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According to FAO, it is estimated t
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Farmer organization as models for p
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NaCSA disseminates BMPs mainly thro
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1. Drain the pond water completely
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Seed transportation and Stocking:
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7. Presently 100% of the society po
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would help in sustaining shrimp sec
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Stress brought about by the capture
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Enhance women participation in aqua
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women in aquaculture and identify a
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major percentage of staff, the need
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having more self confidence through
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Overall status of men and women in
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Compliance to international standar
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(ii) to protect human or animal lif
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c) FAO/WHO Codex Alimentarius Commi
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Annex 1: List of participantsCountr
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Annex 2: AgendaDate Time Presentati
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Annex 3: List of resource persons1.
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