Cytological and genetic analyses provide evidence that spontaneous centric fusion and fission can account for curious patterns of pseudolinkage of two LDH loci in males of brook trout (Salvelinus fontinalis) and in the F(1), F(2) and backcross generations of lake trout (S. namaycush) x brook trout hybrids. Intraindividual polymorphisms for acrocentric and metacentric chromosomes in somatic and gonadal tissue of these fish have been related to the proposed polyploid evolution in Salmonidae