Scoliosis (curvature of the spine) can be caused by many things. See:

http://www.blackwell-synergy.com/doi/ab ... .tb00718.x

Vertebral column abnormalities in brown trout, Salmo trutta L.
SARAH L. POYNTON. Journal of Fish Diseases, Volume 10 Page 53, January 1987

Download the .pdf journal article, there is a picture of a brown trout with similar deformaties