Genetic control of growth in the guppy (Poecilia reticulata)

It is important to consider the genetic control of growth in fish for fish breeding and aquaculture. In the guppy (Poecilia reticulata), the differences of growth were observed among strains, and between sexes, in the closed colonies maintained in the laboratory. The sire and dam variance components affecting the body length at different ages were estimated as a marker of growth by sib analysis. Furthermore, the effective number of loci contributing to the strain differences was estimated from the cross between a small (S) and large (F) strains, focusing on the standard length at 180 days old. The estimated variance component and its change from the maternal and paternal halves were different between females and males. In females, the dam variance components have constantly indicated high values; however, the sire values were low. In males, the sire variance components have high values after reaching 120 days old. In contrast, the dam values, having high values before reaching 90 days old, decreased after reaching 120 days old. The estimated number of loci contributing to the strain differences was 8.0 for females and 1.7 for males at 180 days old from the cross between females in the S strain and males in the F strain. These values were 3.5 for females and a negative value for males from the reciprocal cross. The negative value was due to a lower variance in the F₂ generation with respect to the F₁ generation. From these results, it was estimated that a small number of genes was controlling the final body size of the guppy, and that some of them were probably located on the sex chromosome.