GENETICS AND GROWTH STUDIES OF THE BLUE NEON VARIETY OF POECILIA RETICULATA

Abstract

Males of Poecilia reticulata exhibits striking and complex polymorphisms in the colour patterns on the its body, dorsal and caudal fins. The genes responsible for this polymorphism are predominantly carried on the X and Y chromosomes, The first aim of this project is to study the mode of inheritance of the colour patterns of Blue Neon variety, obtained from two guppy farms in Singapore, Despite many generation of continuous selection by the guppy farmer to develop a pure breeding Blue Neon strain, they have been unsuccessful as the strain remains heterozygous. Analysis of the Blue Neon variety for two local farm showed that the males could be classify into nine different that the phenotype, Turquoise-blue (TB), Turquoise-blue with red tinge ('l'B-R) I Tuxedo (TUX), Tuxedo with turquoise-blue tinge (TUX-TB), Dark blue (DB), Dark blue with turquoise-blue tinge, Dark blue with red tinge (DB-R), Red tail (RT) and Green Neon (GN). The females could be classify into Turquoise-blue (TB), Turquoise-blue with red tinge (TB-R), Dark blue (DB), Dark blue with turquoise-blue tinge (DB-TB) and Greyish hyaline with turquoise-blue tinge (GH-TB). To elucidate the gene control, single pair crosses were set-up between different types of Blue Neon females and wild- type males. Androgen treatment on females of these selected strains provided rapid and efficient information on whether the genes for controlling colour patterns of a particular strain were X- or Y- linked. It is proposed that four major X-linked genes are responsible for the tail colour of Blue Neon. The four genes are Ln (light turquoise-blue iridescent tail colour), Dn (dark blue neon tail colour), Rdt (red tail colour) and Bcp (black caudal peduncle), The expression of these X-linked major genes is affected by autosomal modifier genes. The second study concerned the relationship of growth and the colour genes, Mature Blue Neon males from the two farms were reared in a communal tank and the growth rate of the different phenotypes were monitored. The weights of the various phenotypes were significantly different. Dark blue males was always found to be slow-growing while Blue Neon with a prominent red tinge was found to be more dominant. This could be attributed to either pleiotropic effects or close linkage between Rdt genes and the growth enhancers genes.