Comparison of two methods for measurement of red-area coverage in white-red fish for analysis of color variability and inheritance in ornamental (koi) carp

The purpose of this study was to develop and compare two methods for measurement of red-area coverage in white-red ornamental (koi) carp. One progeny produced by crossing two white-red koi breeders was analyzed. Among 49 fish in the progeny, 7 fish (14.3%) were solid white, 36 fish (73.5%) were white-red, and 6 fish (12.2%) were solid red. The red-area coverage in all white-red fish was determined by analysis of digital photographs using the image editing software Adobe® PhotoDeluxe® Business Edition (method I) and the specialized image analysis software Image-Pro® Plus (method II). The red-area coverage in white-red fish was highly variable, from 0.08 to 68.4%. The difference in red-area coverage for individual fish when comparing these two methods varied from 0.04 to 2.75% with a mean value of 1.03 ± 0.82% (SD). Class distributions of white-red fish with regard to red-area coverage determined by methods I and II did not differ significantly. The obtained data show that both methods can be successfully used for quantitative measurement of color patches in koi. Analysis of frequency distribution of red-area coverage in all fish (including solid white and solid red) showed that fish were clearly divided into two groups with regard to background color: fish with white background (which includes solid white and white-red fish), and solid red fish. The present study confirms that measuring the relative red body coverage gives a valuable insight into the quantitative description of color variability in koi and provides further information for the better understanding of inheritance of this trait. The development and application of new advanced methods for measurement of red-area coverage may stimulate further studies on this subject