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Paddlefish
Paddlefish, closely related to sturgeons, are filter feeders throughout
most of their lives and the only members of the family Polyodontidae
on the continent (4). Paddlefish
have a mostly cartilaginous skeleton guaranteeing no bones in the
meat. Paddlefish grow rapidly, up to 0.75 pounds/month, and can
be easily harvested by seining or gill netting. Paddlefish reproduction
can be induced with hormones to propagate; and fingerlings can be
raised intensively up to stocker size of more than 12 inches in
the same season. Mature female fish (about 20 to 70 pounds) can
produce about 15 percent of their body weight in roe (3 to 10 pounds).
However, there are some disadvantages to paddlefish and their production.
They have poor tolerance for low dissolved oxygen (<2 ppm), and
show handling stress when water temperatures are higher than 70°
F. Artificial propagation and fingerling production are complex
procedures and fingerlings are vulnerable to bird predation (5).
Paddlefish have long been an alternative to sturgeon as a source
of meat and caviar. Formerly abundant in the Mississippi River basin
and adjacent Gulf Coast drainage, natural populations of paddlefish
were commercially harvested for their high-valued, boneless meat
and roe sold as caviar. Continued loss and alteration of natural
spawning habitat, organochlorine (i.e. chlordane and PCB) contaminants,
and overexploitation by commercial fishing are believed to be the
main reasons for declining populations.
The listing of sturgeon and paddlefish species by the United Nations
Convention on International Trade in Endangered Species (CITES)
greatly restricts the importation of sturgeon products from the
Caspian Sea area, the major source for the world's supply of caviar
and sturgeon meat products. As a result, there is an increasing
gap between the demand and supply of those products. In some markets,
wild-caught paddlefish have been substituted for sturgeon because
of their similarity in taste and quality. Producing cultured paddlefish
in the United States would help to meet the consumer demand and,
at the same time, reduce the pressure on natural paddlefish/sturgeon
populations.
Extensive water resources suitable for growing paddlefish exist
in the United States, including millions of acres of private and
public reservoirs throughout the United States built for flood control
management and/or hydroelectric production. Most of those reservoirs
are managed exclusively for sport fish. However, if paddlefish were
permitted to be stocked at 10 fish/acre in just 2,000 acres/year
and with a 75-percent harvest rate, it is predicted that enough
meat and caviar per year (after an initial waiting period of at
least seven years) could be produced to impact the economy by as
much as $7 million a year. Further, with catfish production being
the largest segment of U.S. aquaculture, there are over 175,000
acres of existing catfish ponds in the southern region (1)
where paddlefish could be raised also.
High feed cost is one of the major factors limiting the income
of catfish farmers. However, excess feed and excrement from catfish
make these ponds nutrient-rich and abundant with zooplankton. Polyculture
of catfish with a filter feeding species such as paddlefish could
take advantage of the zooplankton in catfish ponds to increase the
fish yield per acre without adding to the feed cost. Though bighead
carp, a filter-feeding fish native to China, have been introduced
into catfish ponds and have demonstrated yields of 300-500 kg/ha
(6), meat from this species is
not well accepted by American consumers because it has small bones
and a strong fish taste, causing a low market value for this product.
However, paddlefish, a native filter feeding species, provides a
more valuable meat with no bones, a mild flavor and a firm texture
(5).
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