FLUCTUATING ASYMMETRY IN ATLANTIC SALMON, EUROPEAN TROUT AND THEIR HYBRIDS, INCLUDING TRIPLOIDS

Developmental stability as measured by fluctuating asymmetry is report ed to be greater in interspecific salmonid hybrids than in the pure pa rental species. We have examined FA in Atlantic salmon, Salmo salar an d European trout, Salmo trutta and in hybrids between them. FA is sign ificantly greater in meristic traits (number of gill rakers, pectoral fin rays and pelvic fin rays) in hybrids but not in morphometric trait s (length of maxilla, length of head, opercular length and eye diamete r) in which the hybrids show intermediate values. Triploidisation of s almon had no statistically significant effect on meristic FA. Triploid isation of hybrids significantly reduced meristic FA to values close t o those of diploid salmon, thereby reversing the hybridization effect. Triploidisation had little effect on morphometric FA in any of the sa mples. We conclude that FA in meristic and morphometric traits must be considered separately, and the increased meristic FA in hybrids repre sents a break-down of coadaptation as mediated by relational genic bal ance between chromosomes or chromosomal segments.