Relative Resistances of Three Transferrin Genotypes of Coho Salmon (Oncorhynchus kisutch) and Their Hematological Responses to Bacterial Kidney Disease

Abstract

Juvenile coho salmon (Oncorhynchus kisutch) of three transferrin genotypes (AA, AC, and CC) were experimentally infected with the causative agent of bacterial kidney disease (BKD) and mortalities observed. Six experimental and control groups were used: 1) bacteria-infected + no Fe+3; 2) bacteria-infected + low Fe+3 levels; 3) bacteria-infected + high Fe+3 levels; 4) saline control; 5) high Fe+3 control; and 6) low Fe+3 control. In all experimental groups, the AA genotype was the most susceptible to BKD and the CC genotype the most resistant. Addition of exogenous iron did not appear to increase the pathogenicity of the disease. Distribution and uptake of radioiron (59Fe) in control and BKD-infected fish was studied. BKD-infected fish were found to have consistently higher levels of 59Fe in whole blood, plasma, and liver than control fish. In control and experimental fish, spleen, head kidney, and liver tissues were found to accumulate 59Fe, while white muscle and gall bladder tissues did not. The effect of BKD on certain hematological characteristics also was determined. Hemoglobin, packed cell volume, total plasma protein, plasma iron, and plasma corticoid levels all may have decreased with the progression of BKD.