Salinity tolerances and preferences of fry of two species of sympatric sticklebacks: possible mechanisms of habitat segregation

Abstract

During their period of reproductive activity, the sticklebacks Gasterosteus aculeatus (trachurus) and Gasterosteus wheatlandi show differences in their use of available microhabitats in the salt marshes of the St. Lawrence estuary. Gasterosteus aculeatus is found at all stations along a tidal river, Rivière des Vases, while G. wheatlandi is absent from the sites exposed to freshwater. To determine whether the juveniles of these species have different sensitivities to low salinities which could account for their differential distribution, we examined the salinity tolerances of laboratory-reared fry. Adult G. aculeatus (form trachurus) and G. wheatlandi collected at the mouth of the Rivière des Vases were used as the parental stock. For 1-week-old fry of both species, freshwater represented a marginal environment. Following exposure to freshwater for 96 h, G. aculeatus fry showed a 22% mortality while G. wheatlandi showed a significant decrease in growth. By 5 weeks of age, both species were euryhaline. Despite a wide salinity tolerance, field-collected G. wheatlandi significantly preferred a salinity of 7–14‰ while field-collected G. aculeatus fry showed no significant salinity preference.