An Epizootic of Vibriosis in Ecuadorian Pond‐Reared Penaeus vannamei Boone (Crustacea: Decapoda)

A massive ephtic of vibriosis, named “sindroma gaviota” (or sea gull syndrome = SGS) by local shrimp fanners, began in November 1989 and continued through May 1990 in nursery and grow‐out ponds in a number of shrimp farms located in the Gulf of Guaynquil near Cunyaquil, Ecuador. The level of cumulative mortalities ranged from slight in some ponds to more than 90% in others. Examination of affected shrimp, Penaeus vannamei Boone, led to the isolation of several closely related Vibrio species. The predominant species were identified as Vibrio parahaemolyticus, V. vulnificus, and V. alginolyticus using the API‐NFT system. Several of the strains exhibited a transient luminescence and some were positive for urease, an unusual trait for these species. Comparisons of the antimicrobial sensitivity patterns between farm and hatchery isolates from 1989–1990 and hatchery isolates from 1987–1989 indicate that the 1989–1990 pond isolates were not of hatchery origin. The epizootic coincided with the second year of a severe drought in Ecuador. Thus, the discharge of fresh water by the Guayas River was reduced and salinities and relative nutrient concentrations were elevated in the Gulf of Guaynquil. These environmental conditions were ideal for the increased growth of the causative vibrios in the estuarine waters and are believed to be factors that contributed to the 1989–1990 SGS epizootic.