By Hui Gong, PhD*
Guam is an organized, unincorporated territory of the United States in the western Pacific Ocean. The University of Guam (UOG) is a U.S. accredited, regional Land-Grant institution, dedicated to service the communities of Guam, Micronesia and the neighboring regions of the Pacific and Asia.
The Guam Aquaculture Development and Training Center (GADTC) is under the College of Natural and Applied Sciences of UOG. The GADTC is located on Guam’s east coast in Mangilao and on the south side of Fidian Point. The facility is five acres in size, fully fenced on three sides and bordered by a rugged coastline on the Pacific Ocean side.
GADTC facilities include: fresh and salt water wells, an automatic generator back-up system, six 200 m2 concrete ponds, four 200 m2 concrete raceways, three 50 m2 raceways and a 50 m2 concrete pond, numerous fiberglass tanks ranging in size from 0.5 to 20 metric tons, a phytoplankton laboratory, a larval rearing room, and a feed preparation room, in addition to offices, storage spaces, etc.
GADTC’s goals are:
• To conduct applied research in aquaculture.
• To be a training center for the community and provide aquaculture information for the public.
• To serve the needs of stakeholders via technology transfer and extension service.
• To produce high quality fish fry and shrimp postlarvae for the region.
Due to the rapid expansion of the marine shrimp farming industry in Southeast Asian countries in the past two decades and Guam’s favorable location toward this region, GADTC made a strategic decision in 2007 to develop Specific-Pathogen-Free (SPF), genetically-improved shrimp to aim at the tremendous market opportunities and support the Asian-Pacific regional shrimp industry. Since then, GADTC has operated as a fully biosecure facility.
Health status of shrimp at UOG
SPF status of founder populations
Prior to being imported to GADTC during 2007-2008, several founder populations had gone through a strict process to acquire their SPF status. The procedure for establishing SPF status is illustrated here.
Implementation of biosecurity
Upon receiving each founder population, shrimp were held in quarantine station. After shrimp were cleared via a thorough diagnostic analysis by the Aquaculture Pathology Laboratory, University of Arizona (UAZ-APL), they were brought into the breeding center. GACTC’s location provides isolation from casual visitors and other aquaculture farms on Guam, and strict biosecurity regulations have been implemented in maintaining the SPF status of shrimp.
Routine health monitoring
The shrimp samples from GADTC have been submitted to UAZ-APL once to twice annually for disease diagnosis, both by PCR and histopathology. UAZ-APL is the only OIE Reference Laboratory for Penaeid Shrimp Diseases in the United States and is also an APHIS approved laboratory for export testing. All testing of the currently listed diseases (OIE 2OI2 Aquatic Animal Health Code, 15th Edition) were performed according to the OIE guidelines. Since 2003, shrimp of GADTC have been maintained free of diseases including TSV, WSSV, YHV/GAV/LOV, IHHNV, BP, MBV, IMNV and NHP. Since 2014, Vibrio parahaemolyticus, the causative agent of Early Mortality Syndrome (EMS) or Acute Hepatopancreatic Necrosis Syndrome (AHPNS), has been added to the routine health monitoring list, and is absent among the shrimp populations at GADTC.
Guam’s Territorial Veterinarian from the Guam Department of Agriculture is the authorized government official inspecting shrimp health status, examining the diagnostics results and issuing the health certificates for GADTC shrimp.
Shrimp breeding program and related research
In the past eight years, GADTC has established a medium-scale, family-based shrimp genetic improvement program, with fast growth and high survival rates as the main breeding objectives. And the major components are illustrated graphically here. So far, seven generations of genetic selection have been completed, with the number of families per generation ranging from 33 to 75 families.
In each generation, 150-200 shrimp juveniles per family were tagged with Visible Implant Fluorescent Elastomer as family identification, and a communal test was conducted for shrimp of all families. Phenotypic data included harvest weight of individual shrimp and survival rate of each family. Along with pedigree information, genetic analyses were conducted to estimate breeding values for each family and the top several families were identified and best individuals of these families were selected to produce the next generation. Mating designs were optimized to achieve maximum genetic gains for production yield (Growth x SR%) while keeping the accumulation of inbreeding at a minimum. To date, an average genetic gain of about 10% per generation for shrimp production performance has actually been achieved.
At this time, UOG has provided these genetically-improved shrimp broodstock, or candidate juveniles, to five different countries.
Genetic diversity assessment
Since the founder populations originated from different geographic regions and their genetic backgrounds were unknown, we conducted research to develop a panel of 12 microsatellite loci suitable for UOG shrimp stocks, and applied the markers in evaluating the genetic diversity and assessing the accuracy of parentage assignment in the breeding program. The genetic analysis showed large genetic variability among the founder populations, and variation of microsatellite loci was found to be greater than that reported in the previous studies for the same species.
Using the microsatellite markers, genetic variation was evaluated for two consecutive generations. Relatively high genetic variations were found among the families, where Na, Ne and PIC were 10.625, 6.358 and 0.774 for the parents and 10.052, 6.130 and 0.766, respectively, for the offspring. Slight reductions were observed in Ho (0.891 to 0.813) and He (0.804 to 0.792), but such reductions were non-significant between the two consecutive generations, indicating the inbreeding had been effectively controlled in this breeding program.
The microsatellite panel developed also proves to be an effective and accurate tool in parentage assignment for the shrimp breeding program. A panel of 9 markers could predict with 99% accuracy when genotyping error was set at the 1% level, while 12 markers could yield 100% accuracy in parentage assignment.
Other shrimp research
By utilizing the platform of shrimp selective breeding, other shrimp-related research projects were conducted in GADTC, such as development of semi-moist maturation diets using locally available tuna fish roe as a major ingredient and a study of genetic and dietary nutrition interaction, especially the responses of different families of shrimp fed with different dietary protein sources and protein levels under intensive culture systems. The findings revealed a promising potential of genetic selection for shrimp strains which could utilize nutrients more efficiently for aquaculture in the future.
The shrimp breeding program at the UOG’s GADTC has made considerable genetic gains for production performance during the past eight years and shrimp have maintained the SPF status, being free from TSV, WSSV, YHV/GAV/LOV, IHHNV, BP, MBV, IMNV, NHP, as well as AHPNS.
Hui Gong, PhD, is an Associate Professor at the College of Natural and Applied Sciences at the University of Guam. Her expertise in shrimp aquaculture has built on 17 years of experience in applied research in both academic and industrial backgrounds.