Please use this identifier to cite or link to this item: https://scholarbank.nus.edu.sg/handle/10635/153007
Title: CULTURE AND GENETICS OF DOMESTICATED COLOUR PATTERN VARIETIES OF THE GUPPY, POECILIA RETICULATA (PISCES, POECILIIDAE)
Authors: AUDREY ANN FERNANDO-YUEN
Issue Date: 1989
Citation: AUDREY ANN FERNANDO-YUEN (1989). CULTURE AND GENETICS OF DOMESTICATED COLOUR PATTERN VARIETIES OF THE GUPPY, POECILIA RETICULATA (PISCES, POECILIIDAE). ScholarBank@NUS Repository.
Abstract: Singapore is well-known as a breeding centre for tropical ornamental fish, of which the guppy, Poecilia reticulate, is the predominant species. In 1983, S$30.8 million was earned in export revenue from about 700 varieties of these fish. Through careful selective breeding and hybridisation for more than 30 years, about 30 colour pattern varieties of guppy are available locally. Culture of these varieties at 2 integrated and 8 monoculture farms is described. Shallow, concrete aquaria, partially covered by galvanised zinc roofing, are used for breeding; nursery; grow-out of males; and stocking of fish. Water salinities ranged from 0.5 to 9.0%oS, and pH from 7.0 to 8.3. Nylon cage-nets in ponds are used for grow-out of females. In breeding tanks, sex ratios of 1:3, 1:4, or 1:10 males to females are maintained. Juveniles are sexed from 17-21 days; young males and females are reared separately. Guppies feed on diets formulated by farmers, supplemented with live Tubifex spp and Moina spp to adults and fry respectively. Quality of the varieties is maintained by continuous mass selection for uniformity, homogeneity and vividness of colour patterns, large body and fin she, and varied fin shapes. Inheritance of colour patterns, sex-limited to males, of 8 domesticated varieties were examined by reciprocal single pair matings between domesticated varieties with wild-type; and between varieties. Names and symbols of colour pattern gene loci are proposed. The autosomal gene, b. recessive to the wild-type allele, B produces fish with xanthic (blond) body background colouration. Rdt, Blt, and Net genes are non-allelic, and control red, dark blue, and light blue (neon) caudal fin colours respectively. These are inherited as dominant X- and Y-linked genes. Black caudal peduncle, and snake scale-like silvery vermiculatious on body and tail are encoded by Bcp , Ssb and Sst genes respectively; all of which segregated as dominant X- and Y linked genes. Epistatic relationships involving b and Bcp and Blt and Sst; Rdt and Sst Rdt and Net; and Bcp and Ssb,recorded. Crossing-over between Y and X chromosomes, and subsequent selection of some traits in females has resulted in X and Y linkage of colour pattern genes. Modifying genes on either sex chromosomes or autosomes or both enhance the expression of these major colour pattern genes. Selection for quantitative traits, such as large size, and varied tail shapes is of secondary importance. Disc polyacrylamide and· horizontal stard1 gel electrophoretic examination of isoenzymes of 6 domesticated varieties and wild-type was carried out. Of the 7 gene-enzyme systems analysed, XDH, s-MDII, and ADII were polymorphic, while Lilli,G6PD, 6PGD, and SDH, were monomorphic in all stocks. The gene-enzyme loci studied were autosomal. Average number of alleles per locus, and percentage polymorphic loci were higher in domesticated varieties than in wild-type stocks. Genetic distance (D) calculated according to Nei (1972) was higher between domesticated varieties and wild-type, than between varieties. Domesticated varieties appear to have differentiated from wild-type. The higher level of heterozygosity in domesticated stocks is probably due to artificial selection favouring heterozygotes; out-crossing between varieties; and use of large numbers of broodstock in farms. In addition, isolation of wild-type guppies in small pockets in streams could have led to mating between closely related individuals, resulting in erosion of genetic variability.
URI: https://scholarbank.nus.edu.sg/handle/10635/153007
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