Abstract

During 1989, light but persistent mortalities were detected in a turbot Scophthalmus maximus L. farm in Galicia (northwestern Spain) and a virus with the characteristics of a birnavirus was isolated. The purpose of this study was to characterize the viral agent and determine the susceptibility of turbot to this virus. Electron microscopic examination revealed that the particles were isometric, hexagonal and unenveloped with an average diameter of 58 to 60 nm. The molecular weights of the RNA segments were 1.9 and 2.0 x 10 super(6) daltons. The cells most susceptible to the turbot isolate were the CHSE-214, FHM and RTG-2 lines and the optimal temperature range for its replication was 15 to 20 degree C. The RNA and polypeptide electropherotypes show that this virus resembles the Ab serotype of infectious pancreatic necrosis virus (IPNV); however, it differs in that it replicates in the FHM cell line and is not neutralized by antisera to the classical serotypes of IPNV. Infectivity trials conducted in turbot of different sizes indicated that the virus produced mortality only in small fish (2 g), although the larger fish (30 g) harbored the virus for at least 35 d. Fish inoculated with this isolated showed no pancreatic necrosis although necrosis of the hematopoietic elements of the kidney and spleen was detected.