Disseminated neoplasia, or hemocytic neoplasia, has been documented in several marine invertebrate bivalves, including Mercenaria mercenaria. Tumor cells are thought to spread among naive populations through the water column. The disease is characterized by an expansion of atypical, anaplastic neoplastic cells that fill the vasculature. The infiltrating neoplastic cells decrease hemolymph flow and may use vital nutrients leading to organ dysfunction and eventually death of the bivalve. Due to the high rate of infection and dissemination, mortality occurs quickly across dense aquacultured populations, providing high demand for identifying environmental parameters which increase neoplastic hemocyte survivability in order to help farmers maximize their growth and earnings.
Neoplastic cells from surface M. mercenaria clams collected in Wellfleet, Massachusetts, were evaluated for mortality and survival at varying salinities and water temperatures. Highly neoplastic clams were identified as >90% neoplastic via hemolymph (blood) smear. A mixture of hemolymph (containing neoplastic hemocytes) and filtered artificial seawater was incubated for 1 hour. After 1 hour, the mixture was stained with 0.1% Erythrosin B and evaluated for live and dead cell counts using a hemocytometer. Hemocytes were exposed to the following salinities: 0, 10, 20, 25, 30, 35, and 40 ppt at room temperature (22-23°C). For the temperature exposures, neoplastic hemocytes were exposed to 0, 10, 15, 20, 25, 30, 35, or 40 °C while salinity remained constant at 25 ppt.
Survivability was calculated as a percent (surviving/total cells) for each target parameter. Preliminary findings show neoplastic cells had the highest survival rates at mid-range values (30 ppt, 25°C). Lowest survivability was documented at low extremes (0 ppt, 0°C). In contrast, higher extremes saw a slight decrease in survivability from the mid-range water parameters but remained higher than the zeros (ppt, °C). Neoplastic hemocytes of M. mercenaria appear to tolerate a wide range of salinities, suggesting they can survive and spread within a wide range of seawater environments.