Meeting Abstract

P2.46  Wednesday, Jan. 5  Erythrocyte size and relative percentages of blood cells in different size rainbow trout, Oncorhynchus mykiss SHIOSAKI, M.G.*; LAMURE, C.Y.; RODNICK, K.J.; Idaho State University, Pocatello; Idaho State University, Pocatello; Idaho State University, Pocatello shiomatt@isu.edu

Hematological analysis of blood cells in vertebrates is an effective way of discerning whether an organism is healthy or afflicted by a disease. Our study focused on defining the size distribution and percentages of different blood cells in healthy male and female rainbow trout, Oncorhynchus mykiss at different stages of development. Heparinized blood was sampled from the caudal vessels of fish (10-20g, 100-200g, and 1200-2000g) at Clear Springs Foods, Inc. (Buhl, Idaho). The largest group of fish were sexually-mature. The size of the nucleated erythrocytes was determined using a Z2 Coulter counter and by measuring dimensions of stained, individual cells under light microscopy (630X magnification). The relative percentages of common cell type were also recorded from microscopic images of stained cells (400X magnification). Coulter counter data suggests little variation in erythrocyte volume between trout sex and size, with a median value of approximately 240 fL for all fish. The combined percentage of erythrocytes (mature, premature, and senescing) was higher in the largest trout, totaling 96% of cells counted, compared with 90% for both medium and small trout. In contrast, the blood of large trout had a lower percentage of lymphocytes (1%) compared with medium (5%) and small (3.5%) trout. In summary, we documented size consistency of erythrocytes of a 100-fold size range of healthy rainbow trout. The lower number of circulating lymphocytes in the largest fish studied could be due to increased levels of circulating sex hormones or cortisol, all of which can immunosuppress animals during sexual maturation.