Pigmentation in chimeric loach produced by cell transplantation with genetically pigmented and orange embryos

Chimeric fish were produced using two strains of the loach as a model fish and their pigmentation was observed. Transplanting of 50-100 or 150-250 blastomeres from early-mid stage embryos of a wild-type strain to the blastoderm of an orange-type strain generated chimeras, and 60 pigmented chimeras were observed from 3 days after hatching. Pigmentation appears on various regions from head to tail, and the distribution of melanophores was remarkably different among individuals. In the larvae, 57 (95.0%) fish had melanophores on their head region, whereas others only on their trunk and/or tail. Fifteen fish had distinct melanophores on the entire body. In most of the fish, however, the pigmentation gradually became indistinct during further growth. At more than 40 days after manipulation, the pigmentation produced by the transplantation of 50-100 cells could be observed at only one larva out of 14, while those of 150-250 cells could be observed at 62.1% (18/29) and 25.0% (2/8) larvae. When many cells were transplanted to the recipient, the pigmentation tended to remain for more than 60 days. These results indicate that the pigmented period in chimeric fish is particularly associated with the number of transplanted cells.