February 1995					
Contact:  Roger Segelken  (607) 255-9736, hrs2@cornell.edu
Photo Available 

Aquaculture

Ultra-compact system produces affordable fish, Cornell engineers show

ITHACA, N.Y. -- Rearing small and large fish together indoors, feeding
them all they can eat and processing wastes in compact bioreactors
will make fish nearly competitive in price to other meats, Cornell
University agricultural engineers predict.
     An intensive water-recirculation system, with waste-treatment
bacteria living on tiny polystyrene beads that float in a compact
bioreactor, has passed all its tests at Cornell and, when scaled up to
commercial production, could produce tilapia fish for as little as 57
cents a pound.  Michael B. Timmons, professor of agricultural and
biological engineering and co-director of the Cornell Aquaculture
Program in the College of Agriculture and Life Sciences, reported on
the micro-bead bioreactor's success Feb. 2 in San Diego, at the annual
meeting of the Aquacultural Engineering Society.
     "Americans would eat more fish than they do now Ð about 15 pounds
per capita per year Ð if the price weren't so high," said Timmons, who
focused his research on poultry production for 15 years before turning
to fish farming.  "Yield from marine fisheries is declining because
the oceans are practically fished out, and availability of fresh,
farm-raised fish is limited by location:  You can't deliver fresh,
affordable fish year-around everywhere in the United States because
outdoor aquaculture depends on climate."
     Indoor water-recirculation systems for aquaculture are hampered
by cost and complexity, Timmons observed.  So the Cornell
aquaculturists aimed for a fool-proof system so compact that one
module fits in a one-car garage.  Continuous bio-mass loading (or
mixing all fish sizes together while harvesting the largest) is a
proven key to efficient production, the Cornell studies show.  Another
is the high-feeding rate (about 2 percent of body weight a day) so the
fish grow from fingerling size to market in a matter of months.
     But all that fish food produces plenty of waste, particularly
toxic ammonia, which must be cleaned from the recirculated water.  A
20-foot wide tank can yield 30,000 pounds of fish a year but they make
as much sewage as a town of 4,000 people.  Cornell's proposed solution
is a novel microbial filter with a large surface area to hold
waste-eating bacteria as they convert ammonia into nitrites and
nitrates.  Waste-laden water is circulated from fish tanks into
cylinders in which millions of 1-millimeter polystyrene beads Ð
covered with thin biofilms of nitrosomas and nitrobacter bacteria Ð
bob about in floating beds.
     "You need surface area to maintain a large working population of
'bugs' per unit volume," explained William J. Jewell, Cornell
professor of agricultural and biological engineering, an expert in
immobilized bed microbial systems as well as floating bed systems. 
"There are several acres of surface area (on the 1-millimeter beads)
in the 5-foot-diameter filters used in Professor Timmons' systems," he
noted.
     At Cornell, Timmons teaches engineering classes in "Principles of
Aquaculture," and Jewell teaches "Treatment and Disposal of
Agricultultural Wastes."  The Cornell Aquaculture Program, which is
funded by the College of Agriculture and Life Sciences, also offers
three-month internships in fish-farming.
-30-