A survey of cultured penaeid shrimp in Taiwan for viral and other important diseases

Abstract

A survey of disease problems adversely affecting cultured shrimp at farms in Southern Taiwan was conducted in March of 1986. Farms selected for inclusion in the survey were experiencing a variety disease problems in their shrimp stocks, including mortality, poor growth, and reduced food conversion efficiency. Some apparently healthy cultured penaeid stocks were also sampled and examined for signs of subclinical disease. Most of the eight facilities surveyed cultured Penaeus monodon exclusively, although two also contained other species (P. penicillatus, P. vannamei, and P. semisulcatus). These were also sampled and examined. Important virus pathogens found during the survey included the P. monodon-type baculovirus (MBV) found in both P. monodon and P. semisulcatus, and infectious hypodermal and hematopoietic necrosis (IHHN) virus disease in P. vannamei. MBV was the most prevalent major pathogen encountered in the survey, and it was found in samples of P. monodon from seven of the eight locations surveyed and in the single sample of P. semisulcatus. These findings indicate that MBV is a common infectious agent in cultured stocks of these species in Taiwan. The disease hemocytic enteritis (HE) was also commonly observed in shrimp from five of the eight locations surveyed. This may indicate that the disease, which may be caused by an enteric toxin produced by certain types of blue-green algae, is an important disease of cultured shrimp in Taiwan. Also found in the study were two idiopathic syndromes which often, but not always, occurred together in the same shrimp. The first of these syndromes was a generalized diffuse inflammatory disease (II), which was found in several populations of P. monodon and in two stocks of P. penicillatus. The other idiopathic condition, often was observed in shrimp with II, was characterized by hypertrophy of Oka's lymphoid organ, and disassociation and metastasis of spherical clumps of cells derived from the hypertrophied organ. A number of apparently ubiquitous penaeid epicommensals were observed on the gills, appendages, and general body surface of many shrimp sampled in the survey, and some were associated with disease and mortality.