EFFECTS OF SALINITY ON FERTILIZATION SUCCESS IN TWO POPULATIONS OFFUNDULUS HETEROCLITUS

Abstract

A population of killifish (Fundulus heteroclitus) from northern NJ (Newark Bay and Piles Creek, salinity ∼20‰) produces fertilizable ova only if stripped into reduced salinity water, while populations from estuarine areas of Long Island (Montuak and Southampton, salinity 20-25‰) produce viable eggs over a range of salinities (l0-30‰). It was impossible to fertilize Piles Creek eggs in 30‰ even if sperm were already present in the water, but if eggs were transferred from 30‰ to 15‰ within one minute, successful fertilization was obtained. In full strength sea water (30‰) they became artificially activated and produced 90-100% noncleaving eggs, whereas Long Island eggs did not become artificially activated even after two hours in 30‰ salinity. The salinity to which sperm were initially exposed did not appear to affect their ability to fertilize ova from either population.When Piles Creek eggs were stripped into 30‰ salinity in the absence or presence of sperm, SEM observations showed that the micropyles became blocked with extrusions seeming to originate from within the micropylar canal, and in some cases with cortical granules. This blockage very closely resembled the micropylar blockage seen in eggs after fertilization at 15‰ salinity. Ova stripped into 15‰ salinity without sperm generally had no micropylar blockage. This suggests that in the Piles Creek population, contact with full strength sea water rapidly initiates artificial activation, resulting in the blockage of the micropyle.