The Aquatic Diagnostic Laboratory (ADL) at Roger Williams University’s Center for Economic and Environmental Development (CEED) based in Bristol, Rodhe Island, United States, (US) announced that has developed a new diagnostic method that detects hemocytic neoplasia, including early stages of the disease, in Mercenaria mercenaria, a commonly aquacultured hard clam, also known as the quahog.
“This diagnostic method can be done in two weeks and will be a game-changer for shellfish farmers,” said Michael Torselli, an Aquatic Diagnostic Laboratory Research Technician. “It gives a much faster response of whether aquaculture clams have the disease or not, and then that allows farmers to make decisions about what to do with their populations a lot more quickly.”
Common in both soft and hard-shell clams in the region of New England, the disease is a contagious cancerous condition of the hemolymph, which is the clam’s equivalent of blood. While not harmful to humans, the disease causes significant mortality in cultured hard clam populations before harvest by shellfish farmers.
Researchers say that while hard clams are affected by hemocytic neoplasia, they are safe to eat and have no impact on human health. That being said, one of the biggest problems facing shellfish farmers whose clams are affected by this disease is the inability to produce enough shellfish to make aquaculture profitable, since this disease significantly reduces the number of clams available for harvest.
Populations Substantially Impacted
Even when hard clams are the second most valuable cultured shellfish species in Rhode Island and across the region, following oysters, no one has yet quantified the impact of this disease on wild clam populations, or what portion of clam crops are lost to this cancer in the Ocean State, clam populations have been documented to be substantially impacted by this cancer in some areas of Massachusetts waters.
Typically, researchers diagnose the disease histologically, meaning a pathologist reads tissue samples under a microscope, a method that can take up to six weeks and is always lethal to clams. But the RWU ADL researchers have developed a faster, non-lethal method using a quantitative polymerase chain reaction (qPCR) test to analyze hemolymph samples.
Along with the benefit of this being a non-lethal detection method, this diagnostic method also proves to be more sensitive, as it can detect lower levels of the disease, and is less expensive than the traditional diagnostic method.
“We’re hoping a lot of farmers take advantage of the test to be proactive about the disease and how it spreads. This can have a major positive impact on the shellfish industry,” said Torselli.
Five Years of Research and Development
The RWU ADL researchers have developed diagnostic testing methods for other diseases in bivalves, which helped spark the idea for the development of this test by the RWU ADL. The teams identified specific genes within the hard clam genome that are a signature of the disease. After five years of research and development, RWU ADL scientists have successfully created and validated a qPCR test method that detects the disease.
“Once the clams have this cancer, they’re not going to survive for very long,” said Abigail Scro, Aquatic Diagnostic Lab Molecular Research and Lab Manager. “This test will at least let you know that if your clams are market size, that they should be sold quickly.” And she added: “We hope to offer this qPCR method as a routine diagnostic option for farmers using our services at the RWU Aquatic Diagnostic Laboratory, and to have this new method USDA-APHIS certified in the future.”
The development was possible thanks to the grant funding from the Northeastern Regional Aquaculture Center (NRAC) and USDA diagnostic development funding provided to RWU ADL researchers, and in collaboration with researchers at the University of Rhode Island and the Woods Hole Oceanographic Institution.
