Inheritance of the red color in tilapias

The inheritance of the red color was studied in two different varieties of tilapia which are both considered as hybrids of Oreochromis mossambicus. Crosses between red tilapia from the Philippines (PRT) and Sarotherodon galilaeus, or Oreochromis aureus gave a 1:1 ratio of red: normal and crosses between F₁ black fish gave only black offspring. On the other hand crosses between the F₁ red fish gave a 3:1 ratio of red:black and crosses between F₁ red and black offspring gave a 1:1 ratio. These results lead to the conclusion that red color is dominant over the normal black color and controlled by a single autosomal gene (R). A unique phenotype named 'albino with black eyes' was observed among offspring of PRT and a presumed model of inheritance of this trait is proposed. Genetic analysis of a second variety of red tilapia (derived from an unknown origin) showed the following results: crosses between parents and between their F₁ offspring consistently gave 100% red fish and crosses between this red tilapia and Oreochromis aureus gave 100% black offspring. The crosses between red and black F₁ of these last two crosses gave a 1:1 ratio and crosses carried out between the black F₁ offspring gave a 1:3 ratio of red:black. It may be concluded from these results that the black color is dominant in this strain and that this color is controlled by a single autosomal gene (B). The presumed mode of action of the dominant gene (R) as well as of the recessive gene (b) are discussed.