Effects of chronic exercise on growth of transgenic rainbow trout (Oncorhynchus mykiss)

Myostatin is a negative regulatory protein for muscle growth that has been studied extensively in mammals. Decreases in the activity of myostatin and alterations of the associated pathway have been shown to produce heavily muscled, lean phenotypes in cattle and mice, among other species. Several families of transgenic rainbow trout have been generated in our laboratory, each producing non-functional mutations or inhibitors of the myostatin protein. However, the physiology of these fish has yet to be thoroughly investigated.;Exercising fish to improve growth has been well-studied beginning in the 1970s. Because of their commercial importance salmonids have been the subjects of numerous studies investigating the effect of current speed on growth, metabolism and oxygen consumption. Several studies have reported improved growth at specific swimming speeds in rainbow trout, often approximately 0.5--1.5 BLs-1 (body lengths per second). The beneficial effects of exercise include improved growth, reduced stress and reduced aggressive behavior between fish.;Based on previous studies of exercise-related increases in growth, the current study investigated the effect of exercise in fish in which myostatin and other muscle regulatory factors were inhibited. This research focused on the growth, muscle characteristics and gene expression of two families of transgenic rainbow trout, the Prodomain (PD) and the Activin Receptor IIB (ActRIIB) families. Members of these families and their control siblings were exposed to exercise regimens involving either optimum current speeds (0.5--1.5 BLs-1) or little to no current.;Subjects of both trials exhibited significant changes in weight in the exercise groups. Exercise groups in the PD trial also showed more efficient feed utilization and a shift in condition factor distributions. Additionally, expression of the transgene was significantly higher for transgenic individuals in the exercised group.;In the ActRIIB trial, transgenic individuals had significantly higher condition factor throughout and exercised individuals showed increased weight in comparison to non-exercised individuals. Expression of the transgene remained the same throughout the trial for exercised individuals but was significantly decreased for non-exercised individuals potentially indicating a downregulation of TGF-beta ligand activity in piscine muscle growth when exercise is not a stimulating factor.;Ultimately, exercise improved the physical condition of both transgenic and non-transgenic fish, however there was no difference between transgenic and non-transgenic performance in response to either exercise treatment.