title: Effects of shrimp density on transmission of penaeid acute viremia in Penaeus japonicus by cannibalism and the waterborne route.
abstract: To investigate the effects of shrimp density on mortalities of Penaeus japonicus in experimental penaeid acute viremia (= white spot syndrome), shrimp injected intramuscularly with penaeid rod-shaped DNA virus (PRDV) were reared at different densities. In Expt 1, challenged (10(-6) dilution of a PRDV preparation) shrimp were reared collectively in a tank or individually in separate chamber units. A significant difference in cumulative mortalities was found between collectively (75.6%) and individually (1.2%) reared groups after 30 d. In Expt 2, effects of density on mortality were clearly shown when challenged (10(-5) dilution) shrimp were reared collectively in tanks at high (260 shrimp m(-2)), middle (135 shrimp m(-2)) and low densities (73 shrimp m(-2)). The cumulative mortalities for 14 d in the high, middle and low density groups were 72, 46 and 18%, respectively. In Expt 3, challenged (10(-5) dilution) shrimp were reared collectively in 3 tanks (Groups A, B and C) at the same high density (260 shrimp m(-2)): Group A, dead shrimp were immediately removed to avoid transmission of the pathogen through cannibalism and the waterborne route; Group B, dead shrimp were removed at scheduled times but were separated from living shrimp by a net partition to avoid cannibalism; and Group C, dead shrimp were removed twice a day at scheduled times. Resulting cumulative mortalities for 20 d in Groups A, B and C were 4, 24 and 64 %, respectively. These results show that the higher mortalities occur in P. japonicus reared at the higher densities in experimental PRDV infection, and this phenomenon is caused mainly by a higher opportunity of horizontal transmission of the virus through cannibalism and the waterborne route.
authors.affiliation: Laboratory of Fish Pathology, Faculty of Applied Biological Science, Hiroshima University, Higashihiroshima, Japan.
authors.forename: J L
authors.initials: JL
authors.lastname: Wu
authors.forename: A
authors.initials: A
authors.lastname: Namikoshi
authors.forename: T
authors.initials: T
authors.lastname: Nishizawa
authors.forename: K
authors.initials: K
authors.lastname: Mushiak
authors.forename: K
authors.initials: K
authors.lastname: Teruya
authors.forename: K
authors.initials: K
authors.lastname: Muroga
mesh_terms: D000208:Acute Disease; D000818:Animals; D017756:Aquaculture; D002190:Cannibalism; D004267:DNA Viruses / Q000502:physiology*; D018562:Disease Transmission, Infectious / Q000662:veterinary; D033561:Penaeidae / Q000821:virology*; D016133:Polymerase Chain Reaction; D011156:Population Density; D012623:Seawater / Q000821:virology; D016019:Survival Analysis