Virginia Institute of Marine Science
Proceedings of the National Shellfisheries Association
In. the course of laboratory experiments on spawning of mollusks and propagation of larvae and young, Loosanoff and Davis (1950) of the Milford Laboratory of the U. S. Fish and Wildlife Service crossed the southern hard-shell clam, Venus campechiensis Gmelin, with the northern species Venus mercenaria Linne (Loosanoff, personal communication). ·To determine the ecological adaptations of the hybrids, groups of the parent species and their reciprocal hybrids were sent for testing to six laboratories from Maine to Florida, The northern quahog or hard-shell clam inhabits the shores of the Western.Atlantic from·the. Gulf·of St. Lawrence to Florida and the Gulf of Mexico; the southern quahog has been recorded from Chesapeake Bay to Florida (Abbott 1954) although it is doubtful that it occurs naturally in Chesapeake Bay for we have not encountered it. Since the two species cross easily in the laboratory; questions arise about the validity of the species and the amount of natural hybridization which occurs iri areas south of Chesapeake· Bay where the ranges overlap. The characters used by conchologists to distinguish Venus campechiensis are obesity, great width of lunule, thickness of shell, persistence of growth ridges, and absence of purple color internally.
The first series of clams, received in Virginia in May 1954, was planted in screen-covered boxes dug into the bottom at Gloucester Point near the Virginia Fisheries Laboratory. This experiment was a joint project with James B. Engle of the U. s. Fish and Wildlife Service. Although all four groups of clams were of the same age, the hybrids were distinctly larger when received from Milford. In the fall of 1954 when the boxes were first examined, mortality had been high, particularly in the groups containing the smaller clams; some predation was evident. Later in the fall hurricane Hazel dislodged some of the boxes and seriously curtailed the experiment .
Haven, Dexter and Andrews, Jay D., Survival And Growth Of Venus mercenaria, Venus campechiensis, And Their Hybrids In Suspended Trays And On Natural Bottoms (1957). Proceedings of the National Shellfisheries Association, 47, 43-49.