Changes in the hemoglobin system of the coho salmon Oncorhynchus kisutch during smoltification and triiodothyronine and propylthiouracil treatment.

Three electrophoretically separable forms of blood hemoglobin were found in fry of coho salmon (Oncorhynchus kisutch). Ten hemoglobin forms were found in juvenile and adult salmon. Treatment of yearling salmon with triiodothyronine (T3) at 12 ppm in the diet accelerated the increase in concentration of adult forms of hemoglobin, while treatment with T3 at 4 ppm had no effect. Dietary propylthiouracil (1.5 or 5 mg/g) reduced the increases in adult forms of hemoglobin during smoltification. These results implicate thyroid hormones in the expression of adult forms of hemoglobin during the parr to smolt transformation of juvenile salmon.