TRIUMPHS, TRIALS, AND TRIBULATIONS OF SPF SHRIMP BROODSTOCK IN ASIA

Historically, the black tiger prawn, Penaeus monodon, has been the most common shrimp species cultured in Asia.  However, about 15 years ago, an increasing number of Asian shrimp farmers began stocking their ponds with non-indigenous Pacific white shrimp, Litopenaeus vannamei, and the dominance of P. monodon started to fade.  According to the FAO, production of farmed L. vannamei in Asia increased from 2,310 metric tons (MT) in 2000 to 3,156,948 MT in 2015.  This represents a 136,564% increase in L. vannamei production during this 16-year period.  In contrast, production of farmed P. monodon in Asia increased only 14% during the same period, from 623,194 MT in 2000 to 709,601 MT in 2015.  This dramatic species shift can be attributed to a number of factors, including the decline in availability and quality of wild P. monodon broodstock and poor growth and survival of P. monodon grown in ponds.  Importantly, while the production of P. monodon in Asia remained stagnant, broodstock suppliers in the United States began exporting Specific Pathogen Free (SPF) L. vannamei which were selectively bred for rapid growth and high survival, as well as for tolerance to Taura syndrome virus.  The use of SPF L. vannamei broodstock in Asian shrimp hatcheries catalyzed the dramatic species shift away from P. monodon and resulted in significant financial benefits to shrimp farmers using postlarvae produced from these broodstock.  Increased profits resulted from shrimp famers being able to stock their ponds with healthy postlarvae which were free of the major pathogens plaguing the shrimp farming industry.  In addition, because the postlarvae came from selectively bred broodstock, farmers benefited from shrimp that exhibited relatively fast growth and high survival, and L. vannamei were tolerant of much higher stocking densities than P. monodon.

Despite these benefits, there are a number of challenges associated with the use of SPF broodstock.  Imported SPF L. vannamei broodstock are more expensive than locally produced, pond-reared broodstock, so some hatchery operators opt for the cheaper alternative.  Although there are no published data indicating the extent to which pond-reared broodstock are used in Asia, the quantity may be high in some countries.  The negative consequences of using domestic, pond-reared broodstock in the hatchery can be severe due to their unknown health status.  Infected broodstock can spread pathogens both horizontally and vertically in a hatchery, resulting in infected postlarvae which are then sent to the farms for growout.  In addition, pond-reared broodstock, as well as imported SPF broodstock, are of unknown pedigree to the hatchery operator, and the mating of close relatives will cause "genetic erosion" resulting from the rapid accumulation of inbreeding when closely related broodstock are mated.  Offspring produced from such broodstock may exhibit inbreeding depression which manifests in reduced fitness (i.e. lower pond survival, increased susceptibility to pathogens, lower reproductive performance), especially in stressful environments.  There are a number of possible solutions to these challenges, including the establishment of public-private partnerships to better control both the health status and genotypic quality of broodstock available to the industry.