FAMILY SURVIVAL OF PACIFIC WHITE SHRIMP (Litopenaeus vannamei) TO TAURA SYNDROME VIRUS IN FIELD AND LABORATORY CHALLENGES

Taura Syndrome Virus (TSV) occurs in the major shrimp farming regions of the Western Hemisphere and has caused catastrophic economic losses on shrimp farms. In response to TSV problems facing the U.S. shrimp farming industry, the U.S. Marine Shrimp Farming Program (USMSFP) established a selective breeding program to enhance TSV resistance in the Pacific white shrimp, Litopenaeus vannamei. Resistance is assessed by exposing known families of L. vannamei to viable virus (either through feeding of infected tissue or by injection) under controlled, laboratory conditions. However, survival under these conditions may not be predictive of survival in commercial ponds. In addition, family survival may differ among labs because of procedural differences in the challenge test. The objective of this study was to compare family survival of juvenile L. vannamei after exposure to TSV in three USMSFP laboratories and one commercial shrimp farm where TSV was expected to be enzootic because of prior TSV-caused epizootics on the farm.

Eighty families of specific pathogen free L. vannamei were produced at the Oceanic Institute. Of these, 65 families were selected for TSV resistance and 15 families were unselected controls. Representative shrimp from all 80 families were evaluated at the Gulf Coast Research Laboratory (GCRL) where they were exposed to TSV in a per os challenge for 21 days, after which time percent survival by family was recorded. Also, 24 families were evaluated at the University of Arizona (UAZ) where they were exposed to TSV in a per os challenge for 14 days, and 28 families were evaluated at Waddell Mariculture Center (WMC) where they were infected with TSV by injection. In addition to laboratory challenges, 41 families were evaluated at Bowers Shrimp Farm (BSF) in Texas where they were reared in replicate ponds containing TSV-infected shrimp for eight weeks.

Mean family survival at GCRL was 45.1% and ranged from 14.6-93.8%; family survival at UAZ was 21.0% and ranged from 0-82.9%; family survival at WMC was 61.3% and ranged from 20.0- 93.8%; family survival at BSF was 24.4% and ranged from 7.3-57.0%. Regression of mean family survival was significant between GCRL and UAZ (r2 = 0.61, P < 0.001, n = 24), GCRL and BSF (r2 = 0.55, P < 0.001, n = 41), and UAZ and BSF (r2 = 0.68, P < 0.001, n = 16). However, regression of mean family survival was not significant between WMC and GCRL (r2 = 0.08, P = 0.14, n = 28). Family survival was similar in labs using a per os TSV challenge, despite procedural differences between labs. However, family survival was different when TSV was administered via injection. Importantly, these results indicate that per os laboratory challenges provide a tool to evaluate and compare TSV resistance among families of L. vannamei and to predict their performance in farm environments where TSV is enzootic.