Sexual dimorphism in the pectoral fins of a C. inconstans population produces males whose fins are relatively larger than those of females. This difference may result from the unique demands placed on the fins during the male's courtship dance and fanning behaviour during the parental phase. Males and females are also dimorphic in terms of fluctuating asymmetry (FA) of pectoral fin ray number, which is lowest in females. Females with symmetric fin ray counts averaged about 15% more eggs per clutch than females with asymmetric fin ray counts. The ovaries of symmetric females were an average 6.5% heavier than those of asymmetric fish. The difference in fecundity is statistically significant and similar in two samples collected from the same site and separated by a time span of 19 years. This is the first report of a correlation between FA and fecundity in a fish population.