Hatchery trough with paddles.


Some hatcheries have a divider in the middle of the trough
for reinforcement and to allow eggs of different ages to
be incubated at the same time. To provide adequate aera-
tion, troughs are equipped with a series of paddles made
of galvanized tin or similar material. Paddles should be
mounted above the center of the trough on a one-inch
pipe shaft, driven by an electric motor at 30 rpm. Pad-
dles should be spaced at appropriate widths to accom-
modate six to eight wire-mesh baskets in which eggs are
suspended. Baskets made of 4 inch plastic-coated hard-
ware cloth and about 3 inches deep are hung by wires
from the sides of the trough so the waterline is just below
the basket tops. Paddles should be long enough to reach
well below the baskets to gently roll the egg masses and
force oxygen-rich water through them. Water should be
supplied to one end of the trough at a rate that will allow
one complete water exchange in about 45 to 60 minutes
(about 2 to 3 gallons per minute in a 100-gallon trough).
A standpipe may be fitted into a drain at the other end
of the trough to control water depth. The standpipe must
be screened to prevent fry from escaping, and should be
inspected and cleaned often to avoid clogging and trough
overflows. Provisions should be made for emergency
generators to supply power in case of electricity outages.

Water Quality
 Proper water conditions are essential for successful
fingerling production. A clean water source such as a well
is best for hatching eggs, since risk of disease is minimized
if there are no fish or fouling organisms in the water sup-
ply. However, water from many wells and other sources
must often be aerated and warmed prior to filling
hatchery troughs.
 Water temperature should be between 750 and 820 F
(24 and 28 C). Hatching occurs in about 6 days at an
optimal temperature of about 80 F for artificial incuba-
tion. Temperatures from 68 o to 86 F (20 to 30 C) can
be tolerated, but lower temperatures increase the hatching


time and might increase disease problems.
 Oxygen levels in troughs must be maintained at a
minimum of 6 parts per million (ppm) to supply adequate
amounts to eggs and fry. Total hardness and total
alkalinity should exceed 20 ppm, and the pH should be
between 6.5 and 8.5 for best results. Acidic or soft water
can be corrected by adding limestone or a buffer on a
case-by-case basis.
 Further information on water quality is contained in
Florida Extension Circular 715, "Management of Water
Quality for Fish."

Disease Control
 Eggs and fry are highly susceptible to bacterial and
fungal infections. Proper treatment requires complete
familiarity with identification of pathogens and use of
chemicals; additional references and diagnostic
laboratories should be consulted for greater details of
material presented here.
 The best disease control is prevention by maintaining
adequate aeration, clean water, and temperatures below
82 F (28 C). Equipment should be cleaned frequently
and disinfected to prevent contamination. Eggs should
be checked daily and any debris, shells, and dead or badly
infected eggs removed with a siphon. Bacterial and fungal
infections often appear as cloudy or cottonlike patches
on eggs and should be treated or isolated when first
detected. Chemical treatment may be successful provided
standard recommended doses are not exceeded. Con-
version tables and proper dosages are available in Plumb
et al. (Southern Coop. Ser. No. 225) and Jensen et al.
(Alabama Coop. Ext. Service Circ. ANR-327).
 Bacterial outbreaks can be treated by dips or baths in
terramycin (20 ppm), potassium permanganate (3 ppm),
and other drugs. Eggs with fungal infections can be
treated with formalin (100 ppm for 15 minutes) and may
require simultaneous treatment for bacterial growth. For-
malin should never be used with eggs that are near hatch-
ing. Sanitary conditions maintained in the hatchery may
provide added protection from parasites, channel catfish
virus disease (CCVD), and other infections following
hatching.


 Fry Management

Handling Fry
 Within one to two days of hatching young sac fry
should be acclimated and transferred from the hatching
troughs to rearing tanks, troughs, vats, screened boxes,
or other facilities using a /2 inch or larger siphon or small
net. After hatching, sac fry swim through the egg baskets
and school together in tight clusters near the bottom. Fry
rely on their large yolks and do not begin to feed until