Individual measurement of gene expression in blood cells from Rainbow trout Oncorhynchus mykiss (Walbaum)

Most studies that monitor a biological parameter over time in fish are based on the culling of animals and subsequent tissue sampling or the use of complicated surgical procedures such as cannulation of the dorsal aorta. The former method suffers from the large inter-individual variability typically seen in outbred fish, whilst the latter requires highly skilled operators and is not possible with small fish. We describe here a novel and simple method based on non-lethal collection of blood samples from the same individual, allowing improved data quality and reduction in number of animals used without the need for surgical procedures. The frequency and volume of blood collected repeatedly was adjusted to limit the decrease in the percentage of blood packed cell volume (PPCV). The stress response evaluated by measuring the expression of the heat shock proteins 90αb1, 70KDa and the cytochrome p450 family 17 A1 in blood cells by qPCR. Expression levels increased during the PPCV decline and returned to their basal level after adjustment of the sampling procedure. This study demonstrates that a non-lethal sampling procedure can be used for salmonid fish and gene expression in blood cells can be monitored over time from the same individual.