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March 26, 2014
Nurseries for EMS Management
Highly controlled nursery systems—typically raceways, but also tanks—are being used in Latin America to produced larger animals for stocking and to protect the postlarvae from diseases until they can withstand the rigors of pond live. The higher stocking densities and zero water exchange used in these systems demand higher technology, more infrastructure, increased biosecurity, and additional controls and tools. They also require filtration systems, efficient aeration systems, good water quality, the use of microorganisms, siphoning, temperature control, greenhouse structures and better feeds—all with the objective of creating a stable environment for strong, healthy animals.
Nursery managers should have hatchery experience so that they can maintain the required level of control.
The application of probiotics, microorganisms that have health benefits when consumed, is a key component in these systems. The protocols for the different probiotics must be adjusted to the biomass, water quality and the health of the animals.
The feeds used in these systems have to be of hatchery quality. Trying to use growout feeds impacts water quality and subsequently results in bacteriological problems that can lead to poor production performance and weak animals.
Managers of these systems must have the tools and expertise to properly transfer the animals from the nurseries to the growout ponds. Animals must be healthy and strong before transfer; otherwise all the benefits gained in the nursery can be lost. Originally, transfers to ponds were made over short distances. Today, using specially designed pumps that minimize animal stress and mortalities, transfers of up to two kilometers are possible.
The trend today is to lower densities in the nurseries to produce larger animals for stocking.
In Mexico, the impact of early mortality syndrome/acute hepatopancreatic necrosis (EMS/AHPN) was severe. Production dropped approximately 50% in 2013.
According to information supplied by Proaqua Mexico, a leading supplier of specialized aquaculture equipment and feeds, no EMS outbreaks have been reported in nurseries, however, mortalities did develop after animals were stocked in growout ponds.
Some farms stocked nurseries at an average of 1.5 shrimp/liter for 55 days and produced 4.5-gram animals with 80% survival. When stocked in growout ponds at an average of 6.5 animals/m2, the shrimp reached 16 to 18 grams in 30 days. The harvested animals had an average feed-conversion ratio (FCR) of 0.6 and average survival of 85%. The farms managed to get four crops a year with this approach. They produced over 3,000 kg/ha during 2013 with fewer days of culture and lower FCRs.
Several attempts to transfer this nursery concept to countries in Southeast Asia have yielded mixed results. Farmers have tried building nurseries at farms, but with insufficient biosecurity, tools and technology, they encountered problems with size variation, survival and transfers.
Alternative ideas were put in place in Southeast Asia. Stocking in off-bottom cages for 30 days avoided EMS outbreaks. Also, segregating young animals within a 20 to 30% section of pond with nets and then releasing them to the pond after 20 to 30 days has been reported to help.
A successful experience with the implementation of nurseries has been reported in Malaysia with good production performance, successful transfer of the animals to growout ponds and successful harvest in a shorter pond cycle. There is still room to improve by adjusting feeding regimes, probiotic protocols and temperature conditions to achieved better weights in the nurseries.
Source: The Global Aquaculture Advocate (The Global Magazine for Farmed Seafood). Editor, Darryl Jory (firstname.lastname@example.org). Raceway Systems Offer Tools for EMS/AHPN Management. Fernando Garcia (email email@example.com, Epicore BioNetworks, Inc., Eastampton, New Jersey 08060, USA), Fabrizzio Vanoni, William Long and Dirk Lorenz-Meyer). Volume 17, Issue 2, Page 14, March/April 2014.
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