Use of Open Versus Closed Systems in

 Caribbean Prawn Hatcheries


 Dallas E. Alston
 Department of Marine Sciences
 University of Puerto Rico-Mayaguez Campus
 Mayaguez, PR 00708 USA

 The culture ofMacrobrachium rosenbergii, the giant Malay-
sian prawn, has led to Caribbean culturists starting hatcheries
to produce postlarvae as stock. Two systems are primarily
employed: open, which utilize continuous or batch exchange
of water, and closed, which recirculate the water. Open
systems are generally safer since water exchanges can be made
as needed. A disadvantage of open systems is that the hatchery


 El cultivo de Macrobrachium rosenbergii, el camar6n
gigante de Malasia, ha obligado a los cultivadores del Caribe a
empezar sus propios criaderos para la producci6n de postlarvas
para la cria. Los sistemas abiertos y cerrados son los dos prin-
cipales metodos usados. Los sistemas abiertos utilizan flujo
continue del agua o cambios frecuentes de esta. La ventaja de
este sistema esta en el poder eliminar aguas contaminadas


 Mrcrobrachium rosenbergii, the giant Malaysian prawn, has
become an increasingly important culture organism in the Carib-
bean region. Currently, there are prawn farms in Costa Rica, the
Dominican Republic, Honduras, Jamaica, Martinique, Panama,
and Puerto Rico. Most of the culturists prefer to establish a local
hatchery to produce their own stock of postlarvae since importa-
tion on a large scale is prohibitive.
 Macrobrachium hatcheries require brackish water with
salinities ranging from 12 to 19 ppt. Two systems are primarily
employed: open, which utilize continuous or batch exchange of
water, and closed, which recirculate the water. There are many
designs and methods for culture. The choice of a suitable system
should be determined by the availability of a good water source,
the distance from the hatchery to the growout ponds, and the in-
itial investment.


Open Systems
 Open systems are often a logical choice for the majority of
prawn hatcheries since the initial investment is often lower than
for closed systems. A good supply of uncontaminated fresh and
saline water is needed. The site of the open system thus
necessitates that the hatchery be located near a saline water
source, since considerable amounts of water are used in con-
tinuous or batch exchanges of water.
 The intensive labor involved in the culture of the larvae results
in considerable capital input during the culture period. However,
if problems arise during the culture, an open system provides for
complete exchange of the culture water, a practice which may
often save the larvae.
 The hatchery should have a total water storage of at least dou-
ble the larval tank volume. This capacity allows for adequate
water storage for the mixing of the brackish water and provides
space for storing postlarvae before distribution to ponds (New
and Singholka, 1982).

VOL. XX-PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY


 Fernando Ibanfez
 Aquaculture Enterprises, Inc.
 Call Box 5000 Caja 449
 San German, PR 00753 USA

must be located sufficiently near a source of saline water.
Closed system hatcheries can be situated far from the coast,
since the addition of both fresh and saline water is minimal.
Disadvantages of closed systems are the higher initial costs and
difficulty in eliminating contaminated waters.


en un moment determinado. Los sistemas cerrados recirculan
el agua. Los criaderos de sistema cerrado pueden ser instalados
lejos de la costa, ya que el uso de agua dulce y salada es
minimo. Las desventajas de este sistema se deben al incremen-
to del costo inicial y al problema de deshacerse del agua de
cultivo cuando surgeon problems. Los sistemas abiertos
utilizan cambios continuous de agua o en poca cantidad.


 Surface water should be filtered before use in the hatchery.
The filtration process should include a sand filter and then a
smaller mesh filter near the mixing tank (New and Singholka,
1982). Tap water can often be used without filtration, since most
of the water has been treated for human use. Care must be taken,
however, to remove the residual chlorine from the water.
 Ideal sites would be where the wells could be drilled to various
depths to either saltwater or freshwater strata (New and
Singholka, 1982). This could be done along the coast where salt-
water intrusion occurs and forms a wedge beneath the freshwater
strata. Care must be taken if surface water supplies for fresh or
saltwater are to be used. These waters are subject to contamina-
tion and salinity variations. If the hatchery location requires use
of surface water, the water should be carefully checked for
pesticides (New and Singholka, 1982).
 Other water quality parameters should also be monitored.
Prawn larvae require water of extremely high quality because they
are particularly susceptible to toxic ammonia, and to bacterial
and fungal infections (Aquatic Farms, 1979). Postlarvae are
especially susceptible to nitrite and nitrate, both in terms of acute
and chronic toxicity (New and Singholka, 1982). Sublethal effects
of nitrite at levels as low as 1.8 ppm with prawn larvae have been
reported. Reports are that hardness of less than 100 ppm CaCO3
are suitable for freshwater (New and Singholka, 1982).
 Two techniques of open systems are generally employed in
prawn hatcheries. These two methods have been described by
Aquatic Farms (1979) as follows:
Green Water Method
 Phytoplankton is cultured in separate tanks to precondition the
water prior to introduction into the larval rearing tanks. Every
other day, the phytoplankton-rich water is used to replace 50 to
75% of the volume in the larval tanks. With this method, the
phytoplankton continuously "condition" the water (presumably
by taking up the metabolic wastes of the larvae and other food
organisms), and shade the larvae from strong sunlight.


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