A comparative study of muscle texture and intensity of Kudoa thyrsites infection in farm-reared Atlantic salmon Salmo salar on the Pacific coast of Canada

The muscle texture of 32 Atlantic salmon Salmo salar infected with the myxosporean Kudoa thyrsites was compared to the texture of 32 uninfected Atlantic salmon to determine the relationship of K. thyrsites with post mortem muscle deterioration or soft flesh. Flesh texture was evaluated objectively with an Instron texture assessment machine that measured the force required to pass a Kramer 10 blade apparatus through 40 g of muscle tissue. A significant negative correlation (R = -0.45, p = 0.004) was found between the firmness of flesh texture 6 d after harvest and the number of K. thyrsites spores in the muscle tissue. In addition, there was a threshold intensity of K. thyrsites spores necessary before any gross signs of muscle deterioration. The correlation found in this study is highly suggestive that this parasite is a cause either directly or indirectly of muscle deterioration in Atlantic salmon.