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BRISTOL, R.I. – The Aquatic Diagnostic Laboratory (ADL) at ɫ����̳’s Center for Economic and Environmental Development (CEED) 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. 

Common in both soft and hard-shell clams in 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. Hard clams are the second most valuable cultured shellfish species in Rhode Island and across the region, following oysters; while 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.

“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, who received his bachelor’s in Marine Biology and Environmental Science from RWU in 2016 and his master’s in Environmental Science from the University of New Haven in 2019. “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.”

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,” said Torselli. “This can have a major positive impact on the shellfish industry.”

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. With grant funding from the  (NRAC) and  diagnostic development funding provided to RWU ADL researchers, and in collaboration with researchers at the University of Rhode Island and the , 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.

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.  

“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.”

“We would like even an earlier warning system someday,” said Scro, who received her bachelor’s in Marine Biology and Mathematics from RWU in 2015 and her master’s in Fisheries & Aquatic Sciences from the University of Florida in 2021. “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.”

As for what causes this cancer in clams, researchers don’t know yet. However, they believe this technology will help long-term monitoring and hope that when their findings are published, other labs can adapt it for their uses, whether it be conservation, aquaculture, or research.