February 15-18, 2009 Washington State Convention Center Seattle ...

APPLICATION OF SCALE COVER GENE N FOR IDENTIFICATION OF PLOIDY IN
ORNAMENTAL (KOI) CARP
Boris Gomelsky*, Kyle J. Schneider and Robert P. Glennon
Aquaculture Research Center
Kentucky State University
Frankfort, KY 40601 USA
boris.gomelsky@kysu.edu
Production and stocking of sterile triploid ornamental (koi) carp might be useful in cases when fish reproduction is undesirable.
The common way to produce triploid fish is suppression of the 2 nd meiotic division in eggs by application of strong physical
treatments (temperature shocks or hydrostatic pressure). Usually applied physical treatments do not provide 100% triploids in
progenies; therefore the ploidy of each fish should be verified by analysis of blood sample. It would be beneficial to develop a
method of ploidy determination based on some external morphological trait.
Appearance of four scale cover types (scaled, mirror, linear or leather) in koi (and common carp) results from the interaction of
two genes having two alleles each (S/s and N/n). Experiments on induced meiotic gynogenesis revealed a very high recombination
rate of gene N; almost 100% of gynogenetic fish resulting from a heterozygous female (Nn) are heterozygous. This study
suggested using this peculiarity of gene N to determine fish ploidy.
Eggs taken from a leather koi female (genotype ssNn) and sperm taken from a scaled koi male (SSnn) have been used for
production of control (no shock) and heat-shocked progenies. The 2-min heat shock (40º C) was applied 6 min after insemination.
Fish segregation in control progeny (288 scaled : 315 linear) did not differ significantly from the expected ratio 1:1. Fish
segregation in heat-shocked progeny (179 scaled : 404 linear) was significantly shifted towards the prevalence of linear fish.
This shift in ratio may be explained by the suggestion that due to high recombination frequency of gene N, the suppression of
2 nd meiotic division results mainly in triploids with genotypes Nnn, while scaled fish nn should be mainly diploid. In heatshocked
progeny about half of linear fish had less profound reduction of scale cover compared with typical linear fish. It was
suggested this group (called multi-scaled linear) are triploid fish (Nnn) which differ from typical diploid linear fish (Nn) due
to incomplete dominance of allele N.
These suggestions have been generally confirmed by analysis of fish ploidy based on measurements of erythrocyte nuclei by a
Coulter counter. All analyzed (n=20) scaled and typical linear fish from heat-shocked progeny were diploid while from 15 analyzed
multi-scaled linear fish 14 fish were triploid and 1 fish was diploid (Figure 1). The practical applicability of this method
of ploidy determination will be discussed.
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