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Black blotching of the skin in red tilapia is undesired by tilapia producers since it affects their marketability. This study was carried out with the aims of mapping the blond locus and testing whether the homozygous recessive blond gene reduces or removes blotching in red tilapia by studying the interaction between the red and blond genes. Two types of mapping families (two intraspecific and one interspecific) were used for the mapping of the blond locus. Genome-wide mapping using microsatellites was first carried out to identify molecular markers that were linked to the blond locus. The locus was mapped in linkage group (LG) 5 in an interval that varied between 7.5 and 20.8 cM, depending on the tested family. In the intraspecific families the blond locus was closely linked to the microsatellites UNH309, UNH169 and GM017 ( P < 10 − 11 ), while in the interspecific family microsatellite GM636 ( P < 10 − 8 ) was also found to be significantly associated, in addition to the above three microsatellites. Linked markers were used to identify the genotype of individual fish for the blond and red loci from the specifically designed crosses so the effect of recessive blond gene on blotched fish could be assessed. The underlying blond trait did not significantly reduce the area of blotching but did reduce the saturation (paler blotching) and enhanced the redness of body colour in the homozygous blond fish compared to the heterozygous (wild type) group. [ABSTRACT FROM AUTHOR]

In temperate zones, energy reserves of fish are closely related to survival during the first winter of their life. In this study, the genetic and phenotypic background of the accumulation, mobilization and utilization of energy reserves was investigated in Amur mirror carp. To achieve this, the role of traits related to energy reserves on fish performance during the first winter and further periods of rearing was investigated. The experimental stock was established by four full-factorial matings of 5 dams and 10 sires to generate up to 200 full-sibling families. The offspring were sampled before and after the first winter rearing period. Seasonal variation in direct and indirect measures of energy status was examined using Fulton's condition factor (FC), hepato-somatic index (HSI), visceral index (VSI_NO), glycogen, fat and protein in hepatopancreas (HP) and muscle fat content. Other performance traits were also recorded (weight, resistance to koi herpesvirus disease). All traits related to energy reserves, except HP protein, were significantly lower after the first winter. Overall, HP glycogen and fat from muscle, HP and viscera were mobilized during winter. However, genetic correlations between same traits recorded in autumn and spring were lower than 0.8 for most of the traits, implying that not all families responded to overwintering in a similar manner. Heritability also differed before and after the first winter. Before the first winter, all traits had low to medium heritability (0.05–0.35), but after the winter the same traits were moderately or highly heritable (0.22–0.58). Interestingly, HP glycogen traits, unlike HP fat and HP protein, and HSI recorded in yearlings were positively genetically correlated with survival during the third growing season (r g = 0.49–0.72). This study provides the first evidence of a genetically based strategy for energy mobilization related to overwintering of common carp. Measuring of FC and HSI could be used to monitor the energy status of common carp and to provide a supplementary tool for management of carp stocks. • Hepatopancreas (HP) glycogen traits were positively correlated with survival at market size, unlike HP fat and protein. • Condition factor and hepatosomatic index provide relatively adequate way of evaluating the energy reserves status. • Energy status of carp very likely does not correspond to Koi herpesvirus disease resistance. [ABSTRACT FROM AUTHOR]