Salinity tolerance and resistance of the Pacific lion's paw scallop Nodipecten subnodosus, using the median lethal concentration method (LC₅₀) and a gradual change method were measured. We also attempted to demonstrate whether salinity and temperature, pH, dissolved oxygen and turbidity control the distribution and densities of species within a coastal lagoon (Laguna Ojo de Liebre, Mexico). The upper and lower LC₅₀ of this scallop were determined in the laboratory at predetermined times over 4 days (96 h) when exposing specimens to salinities of 15, 20, 25, 30, 37, 42, 47, 50 and 60 ppt. The upper and lower salinity resistances were studied by subjecting the specimens to either increases or decreases of salinity by 3 ppt every 3 days, departing from a normal salinity of 37 ppt. Salinity, temperature, pH, dissolved oxygen, and turbidity of the water close to the bottom were measured once a month from January 2001 to March 2004 at 20 stations located along the shore of the lagoon. Results showed no statistical differences at the upper or lower LC₅₀, at 24, 48, 72 and 96 h, and the species salinity tolerance varied from 23.5–24.2 to 50.4–53.8 ppt. Salinity resistance, measured by the gradual change method showed no mortality in the 22–52 ppt range, but abrupt mortality occurred with exposure beyond this range. Comparing these results with field data, we concluded that our results provide evidence that salinity is not a limiting factor regulating distribution and density of adult Pacific lion's paw scallop in the lagoon. Food quality and availability, water currents and substrate could be limiting factors.