Plankton-Mediated Oral Delivery of Vibrio anguillarum Vaccine to Juvenile Ayu

Abstract

Juvenile ayu Plecoglossus altivelis are very sensitive to handling stress. For this reason, it is difficult to immunize the fish using immersion or spray delivery methods. In order to immunize these juvenile ayu against Vibrio anguillarum infection, oral delivery was attempted using feed plankton as a mediator of the vaccine. Two zooplankton species: water flea Moina macrocopa and brackish water rotifer Branchionus plicatilis were examined on their intake of the bacterial antigen. The water flea incorporated three kinds of V. anguillarum antigens: formalin-killed cells (FKC), formalin-killed and washed cells (FWC) and heat-killed cells (HKC), but the rotifer incorporated only HKC. One g of wet live water flea incorporated at most 520 pg lipopolysaccharide (LPS) of FKC for 30 min when FKC was added at a concentration of 1,400 pg wet FKC/10 water fea/m/ culture water. The rotifer lost HKC easily by a few washings. Seventy-three-day-old juvenile ayu weighing an average of 63 mg incorporated 0.64 pg LPS (81 pg wet FKC)/fish in 2 h after FKC-fed water flea was given. Both the vaccinated fish by feeding FKC-fed water flea for 22 days and the unvaccinated fish fed untreated water flea were challenged with V. anguillarum by water-borne infection. The vaccinated and unvaccinated fish showed 92.4% and 64.2% survival rate, respectively, and this result indicates juvenile ayu efficiently incorporated the antigen and acquired protective immunity against vibriosis. © 1989, The Japanese Society of Fisheries Science. All rights reserved.