World Aquaculture Magazine -December 2021

68 DECEMBER 2021 • WORLD AQUACULTURE • WWW.WA S .ORG that is under the spotlight has focused on disease resistance for a decade. Starting from a WSSV-tolerant line that was quarantined at the University of Arizona, the shrimp have been maintained and selected for generations. Over the years, the breeding program gradually evolved its selection method frommass selection to family- based selection to modern genomic selection. Sufficient data were accumulated to define this disease-resistant line from multiple angles. Using this shrimp population as an example, adopting the elements of genomic selection, a profile of a disease-resistant line should contain three characteristics: field/pond survival, specific pathogen challenge survival and a genomic signature. Pond Survival Although the field data are the most popular and widely accepted, shrimp performance is the result of complex factors ranging from operation to climate. Unless a side-by-side comparison is conducted with as many human-controlled variables as possible, most of the field feedback cannot confirm the resistance of tested lines due to lack of statistical power. However, large sample size (e.g., millions), a long duration (e.g., multiple generations) of S hrimp farming has long suffered diseases for decades. Robinson and Lillehammer (2020) even call it the “global viral pandemic in shrimp.” This pandemic threatens social sustainability by dramatically reducing the income of farm- ers and their communities; it also damages environmental sustainability due to excessive use of antibiotics and chemi- cal treatments (World Wildlife Fund, n.d.) in fear of diseases. In addition to the development of better treatments and better vaccines, shrimp companies quickly realized the value of genetically disease-resistant shrimp lines. The question of how to breed disease-resistant lines has been researched, taught and practiced. Selection for disease resistance has a long tradition in aquaculture. The recent achievement of applying genomic selection for white spot syndrome virus (WSSV) resistance in whiteleg shrimp (Lillehammer et al. 2020) demonstrated that breeding of shrimp can be as sophisticated as that of cattle or poultry. However, very little is known about what a disease-resistant line should look like. One approach to address this question is by investigating a commercial line that has both proof of resistance in the field as well as elegant and comprehensive laboratory data. In this case, the line The Characteristics of a Disease-resistant Shrimp Line: From Quantitative Observation to Genomic Signature E Hu TABLE 1. The resistant line survival data from the field. Ca s e Te s t ed L i ne Dens i t y (PL/m 2 ) Sur v i va l (%) PL Quan t i t y 2013 Mexico Resistant line 11.9 82.3 Control 11 20.2 2015 Mexico Resistant line 16.9 72.3 27,650,000 2015 China Resistant line 83.0 500,000 Control 41.2 500,000 2016 China Resistant line 78.3 1,520,000,000 Control 30.0 2016 Malaysia Resistant line 80.9 58,000,000 FIGURE 1. Disease challenge survival rates of the resistant line in different years. Disease challenge was performed by the University of Arizona.