European green crabs, Carcinus maenas, infected with trypanorhynch plerocercoids, Dollfusiella martini were studied to determine whether larval cestodiasis had an effect on the digestive enzyme activity of the green crab host. We collected 28 green crabs from Swan Bay, Victoria, removed their digestive glands, counted the plerocercoids and assayed the digestive gland for three enzymes: trypsin, lipase, and a-glucosidase. Regression analysis showed a significant negative relationship between levels of infection and the specific activity of trypsin (r(2) = 0.17, d.f. = 1,22, p < 0.05, y = -3.91E-06x + 1.683E-04) and lipase (r(2) = 0.40, d.f. 1,23, p < 0.001, y = -2.89E-05x + 1.615E-03), i.e., the higher the level of infection, the lower the trypsin and lipase activity. No relationship was found for alpha-glucosidase activity. We also found a positive correlation (r(2) = 0.41, d.f. = 27, p < 0.05) between intensity of infection and host size, a common host/parasite phenomenon. We conclude that infection by plerocercoids of the trypanorhynch, Dollfusiella martini, adversely affects digestive gland function of green crabs by reducing the specific activity of the digestive enzymes trypsin and lipase. This reduction in enzyme activity may be attributed to the destruction of enzyme producing F-cells resulting from plerocercoid infection of the digestive gland.
