Occurrence of polyploidy in the fishes

Polyploidy, the multiplication of entire setsof chromosomes beyond the normal set of two,has occurred extensively, independently, and isoften repeated in many groups of fish, from thesharks to the higher teleosts. While there areseveral ways that a polyploid fish can develop,environmental change and hybrid stabilizationmay play a large role in the initiation of anew polyploid species. Despite its prevalence,the importance of polyploidy in the evolutionof the fishes is unclear. Polyploidy is morecommon in the lower teleosts than the higherteleosts, possibly due to an advantage gainedthrough decreased specialization in the lowerteleosts, a decreased viability of polyploidyin the higher fish, or both. Polyploid fishcould gain an advantage over diploid fishthrough increased heterozygosity, divergence ofduplicate genes, and/or increased expression ofkey physiological proteins. While polyploidfish do not differ considerably from diploidsphenotypically, they may be at a disadvantage,or certain advantages may be lessened due to anoverall decrease in cell number. This papersummarizes all polyploid species of fish knownto-date, and discusses the possible roles andpathways for establishment of polyploidy in theevolution of the fishes.