Myosin expression levels in trout muscle: a new method for monitoring specific growth rates for rainbow trout Oncorhynchus mykiss (Walbaum) on varied planes of nutrition

Fish growth is manifested by a number of measurable physical changes. We have developed a sensitive method for monitoring the growth rate of fish fed at four different planes of nutrition. This technique consists in measuring expression levels of myosin RNA isolated from the muscle of experimental animals. Using PCR (polymerase chain reaction) primers, and a fluorescence-labelled single-stranded DNA probe that hybridizes specifically to a region within the myosin mRNA of rainbow trout Oncorhynchus mykiss (Walbaum), we were able to detect differences in the relative level of myosin expression between groups of fish. This method also allows for the determination of absolute expression levels when reactions are performed with standards consisting of known levels of in vitro-transcribed myosin RNA. With the proper equipment, this novel procedure can be performed rapidly on large numbers of individuals, and with the procurement of non-invasive muscle biopsies the same experimental animal could theoretically be sampled multiple times throughout the course of the study. This new method could be used to measure differences in muscle synthesis in fish associated with various nutrient intake levels, environmental parameters, life-history stages and health status.