Karyotypic analysis of 2 sympatric species of fish, Fundulus heteroclitus L. and F. majalis

A chromosome study was performed on 2 sympatric species of marine fish, Fundulus heteroclitus L. and F. majalis . A modification of techniques which included the combination of the procedures of McPhail & Jones (1966) with those more recently developed by Ohnuki (1968), for demonstrating the spiral structure of cultured human leukocytes, resulted in clear and distinct chromosome spreads from gill epithelial cells of these 2 species. Optimum chromosome spreading and accumulation of metaphase figures resulted when specimens of F. heteroclitus received either a 0·28 ml or a 0·4 ml injection of a 0·1 % colcemid solution for 45 h and 48 h respectively. Best results in F. majalis occurred when specimens received a 0·1 ml dose of the 0·1 % colcemid solution for 22 1/2 h. Studies of the karyotypes of 18 specimens of F. heteroclitus and 9 specimens of F. majalis indicated that the 2 N chromosome number for each species was 48.