Meristic comparisons of populations of mummichog Fundulus heteroclitus (L.) from Sable Island and mainland Nova Scotia

Abstract

Mean counts were recorded for gillrakers, fin rays, and vertebrae in samples of mummichog Fundulus heteroclitus (L.) collected from a freshwater pond (0.05‰ salinity (S)), a brackish pond (16‰ S), Sable Island, 290 km east of Halifax, Nova Scotia, and a sample collected along the coast near Halifax (26‰ S). Virtually all differences were statistically significant. Mean counts for gillrakers and rays of all fins were lowest in the sample from the brackish pond. Counts of trunk vertebrae were relatively stable but counts of caudal and total vertebrae decreased along the gradient of increasing salinity. The frequency of mummichog with anomalous vertebrae, principally in the caudal peduncle, was also least in the sample from the brackish pond and highest in the freshwater sample. Although the effects of temperature and other important variables cannot be removed from these observations, the consistent trend of structures such as fin rays and gillrakers which are differentiated relatively late in the embryonal phase suggests that osmotic stress, which should be minimal near 16‰ S, is also involved in the regulation of differentiation.