Infectivity and effects of gypsy moth and spruce budworm nuclear polyhedrosis viruses ingested by rainbow trout

Rainbow trout fingerlings were fed dried krill injected with gypsy moth or spruce budworm nuclear polyhedrosis virus (LdNPV and CfNPV, respectively) at a total dose of 1.4 x 10(7) occlusion bodies (OBs) per fish. By the end of the 21-day experimental period there were no adverse effects on fish survival or behavior and no significant differences in feeding rates or growth between treated and control fish. The internal organs of all fish were examined at the end of the experiment and there were no signs of lesions, discoloration, swelling, hemorrhaging, or other aberrations. Visceral tissues were analyzed with a horseradish peroxidase-labeled whole genomic DNA probe (enhanced chemiluminescence procedure) to detect infection by the NPVs. There were no indications of NPV infection (no positive signals) in stomach and intestinal tract tissues of treated fish. High background signals were obtained from liver samples, but further analyses indicated that these were not due to the presence of LdNPV or CfNPV. The protocols outlined here should be applicable to determining infectivity and effects of genetically modified insect viruses on fish.