Abstract
Samples of Abra nitida were regularly obtained from a site at 100 m depth in the Skagerrak from 1970 to 1977. Individuals were examined for their degree of reproductive development on the basis of the number, development stage, and size of the gametes. A mean index of gonad development was calculated for each sample. All individuals of over 10 mm shell length were sexually mature. Samples of individuals over this size revealed some degree of spawning activity throughout the whole year. However, the autumn months in particular were characterized by increased numbers of spawning individuals, though this varied considerably in extent from one year to another. These results are compared with data for other Abra species, in particular A. alba. It is suggested that A. nitida undergoes plankto-trophic larval development with a long pelagic life, and that such development may explain observed fluctuations in A. nitida populations.