World Aquaculture Magazine - June 2020

WWW.WA S.ORG • WORLD AQUACULTURE • JUNE 2020 29 ( C O N T I N U E D O N P A G E 3 0 ) FIGURE 3. Pond reared blue shrimp Penaeus stylirostris . Pathogen Detection and RNAi Antivirals in Shrimp Breeding Melony Sellars Disease is the biggest unknown risk in shrimp aquaculture, with a growing list of commercially devastating disease-causing pathogens around the world. Pathogen detection and screening has been fundamental to understand these pathogens, determine how to manage them during culture and develop successful shrimp breeding programs. Recently, the use of RNAi antivirals—double- stranded RNA injected into broodstock—has also started to play a role in developing pathogen-free breeding stocks. Pathogen detection, screening and RNAi antivirals are being used in shrimp breeding and shrimp production globally. ShimpMultiPath is a high-throughput disease screening platform now on the market. Shrimp Genetics Now and in the Future Kyle Margin Historical global production of shrimp has seen enormous growth, with a typical cyclical pattern in production volumes. This cy- clical pattern is mainly caused by increasing and varying disease pres- sures compensated by new developments in technology in husbandry, feeds and genetics. Worldwide shrimp farming is now heading towards controlled production and intensification, in line with historical de- velopments in longer-established domesticated terrestrial and aquatic species, to create stable production. The shift to intensive controlled environments also requires breeding programs to change. Genotypes interact with culture environment and breeding programs can use this to optimize production in specific environments. To further improve the rate of change and to maximize production, large-scale shrimp breeding programs should implement the latest genomic technology. Integration of genomic selection in breeding programs for terrestrial and other aquaculture species has enhanced the rate of genetic improvement. Similar changes in the rate of genetic improvement can be expected for shrimp. However, integration of the multiple “omics” resources now available (genome assemblies, transcriptomes, linkage maps, and proteomes) into genomic selection is likely to be critical to exploiting these currently isolated resources. In shrimp this integration is much less advanced than in other aquaculture species. Available shrimp genetic resources include a 2017 linkage map covering 98 percent of the genome (~5000 SNPs) and a 2019 genome assembly covering 87 percent of the genome (1.66 Gb). Studies have confirmed strong QTL linked toWSSV resistance. Accurate genomic selection using the c3200 marker for body weight started at Kona Bay in 2020. Why Asian Shrimp Farmers Grow PacificWhite Shrimp: A Reminder of Hawaii’s Recent Past ShaunM. Moss In 1981, IHHNVwas first identified on a shrimp farm in Hawaii causing mass mortalities in captive L. stylirostris (Fig. 3). IHHNVwas also detected in a population of L. vannamei cultured at the same farm but this shrimp species appeared refractory to the virus. The high susceptibility of L. stylirostris to IHHNV and the relative tolerance of L. vannamei to this pathogen helped catalyze L. vannamei to be the dominant farmed species in theWestern Hemisphere. In 1984, the USMarine Shrimp Farming Program (USMSFP) was formed as a congressional initiative to solve problems constraining the US shrimp farming industry. The USMSFP consisted of member institutions including Oceanic Institute (OI) in Hawaii and the University of Arizona (UAZ). Because of the relative tolerance of L. vannamei to IHHNV, the USMSFP decided to commit resources to develop culture technologies for this species, including its domestication. Although IHHNVwas not lethal to L. vannamei , infected populations exhibited Runt Deformity Syndrome resulting in growth suppression and cuticular deformities. It became apparent that IHHNV caused an economically significant disease in L. vannamei and that efforts to rid captive populations of this pathogen were critical to its domestication. In 1989, OI and UAZ began developing the world’s first Specific Pathogen Free (SPF) population of L. vannamei which was free of IHHNV and other pathogens. Offspring from SPF broodstock were evaluated at commercial farms in the US and significantly outperformed non-SPF shrimp. OI began supplying SPF broodstock to US farmers and, by 1992, more than 95 percent of farms in the US were stocked with offspring from these broodstock, resulting in bumper crops from 1993-1995. In 1994, OI started the world’s first family-based breeding program to improve shrimp growth and survival, as well as tolerance to Taura Syndrome Virus that devastated US farms in 1995. OI generated basic information about the quantitative genetics of shrimp breeding and distributed SPF, selectively-bred shrimp to the US industry. Between 2000-2010, OI distributed more than 2.5 million shrimp to US stakeholders, including Hawaii broodstock suppliers who developed their own robust breeding programs. Hawaii broodstock suppliers played a critical role in catalyzing a paradigm shift in Asian shrimp farming. Between 2003-2018, Hawaii broodstock suppliers provided ~ 5 million SPF, selectively bred L. vannamei broodstock to Asian shrimp hatcheries. In 2000, Asian shrimp farmers produced an estimated 623,194 t of black tiger shrimp, whereas production of L. vannamei was only 2,310 t. By 2017, P. monodon production increased by 18 percent to 733,525 t, whereas L. vannamei production skyrocketed by 158,500 percent to 3.66 million t valued at $22.7 billion. This dramatic change is attributed, in large part, to the commercial availability of SPF, selectively-bred L. vannamei originally developed by the USMSFP and commercialized by Hawaii broodstock suppliers.