Texas Game and Fish, Volume 6, Number 2, January 1948 Page: 7
18 p. : col. ill.View a full description of this periodical.
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Cutting Down Minnow Losses
Handling of
By John DobieMinnows
BAIT dealers are often troubled with a
heavy loss of minnows in holding
tanks. Studies by the Fisheries Research
Unit of the Minnesota Division of Game
and Fish show that most losses result from
injury to fish during seining, shock caused
by improper tempering, suffocation from
inadequate aeration or temperature con-
trol in holding and transporting tanks, and
the disease that abounds in unclean tanks
overcrowded with minnows. The warm
water in lakes and the injury from wave
action produce a high loss of minnows in
live boxes. Some dealers have noticed a
heavy mortality when stream minnows
have been held in ponds not suited to
their needs. For minnows held in small
tanks, prevention of injury and disease
infection are the only practical methods of
reducing loss. There is no magic formula.
Prevention of injury must start at the
time of seining. The net should be landed
along a solid bottom whenever possible in
order to avoid the roily water that is so
injurious to fish. A seine full of fish should
never be pulled up on shore but should
be bagged loosely and floated to deeper
water for sorting into floating live boxes.
When the fish are being transferred to the
truck tank, neither the dip nets nor the
carrying containers should be overloaded.
"Soft" minnows, like the golden shiner,
should never be seined during hot weather
because the mortality is too high. They
can be harvested by means of a baited
drop net hung with cheese cloth to mini-
mize the injury. Dip nets used to transfer
fish should also be covered with a soft
material.
Slow tempering is the most important
method of preventing loss of minnows.
Fish have no means of adapting themselves
to rapid changes of temperature. A sud-
den change of more than ten degrees F.
will give the fish a fatal shock, though
death may not occur for several hours or
even until the next day. As fish can be
hauled better in cold water than in warm,
it is often necessary to transfer the min-
nows from the warm lake or stream to the
cold water of the truck without injuring
the fish. Safe tempering requires at least
20 minutes for each ten degree change
in temperature. A small diameter syphon
hose will mix these waters at a gradual
rate, but a thermometer should be used
to determine the differences of tempera-
ture.
Minnows will stand the strain of trans-
portation best when the hauling equip-
ment is carefully designed. The tank
should be of sufficient size to handle the
number of minnows to be carried, and the
inside should be smooth enough so that
the fish will not suffer injury. The aeration
system, whether oxygen or sprayed water,
must supply a minimum of three parts of
disolved oxygen per million parts of water
when the tank is fully loaded with fish,but a concentration of five or six parts is
preferable. The fish are more hardy at
low water temperatures so the water in
the tank should be maintained at 65 F.
or lower, especially when the fish are
hauled long distances. Missouri minnow
dealers often haul fish 1,000 miles in truck
tanks insulated with four inches of cork,
which are iced when necessary along the
route. Minnows that have been "hardened"
for 24 hours in cold water will stand long
hauls much better than fish taken directly
from warm water.
The greatest loss of minnows will be
noticed in the holding tank, but most of
it is due to an accumulation of seining and
handling injuries. The ill effects of rapid
tempering will become apparent by the
time the fish are transferred to the holding
tanks. Since the minnows will remain in
the holding tanks for a number of days,
the tanks should be operated so as to mini-
mize injury and disease infestations.
The holding tanks should be smooth on
the inside so the fish will not lose scales
when rubbing against the sides and to
facilitate cleaning and sterilization opera-
tions. The aeration system must maintain
at least three parts of dissolved oxygen
per million parts of water when the tank
is full of fish, and the tank should be deep
enough so that the fish are not injured by
the stream of water from the jets.
The water for tanks should be filtered
(spring water is filtered by nature). A
number of small tanks are more desirable
than one large one. Diseases can be con-
trolled better because fewer fish are held
in one place and the turnover is more
rapid. The tank should be small enough
so that the entire contents can be sold in
four to six days. No additional fish should
be added until the original lot has been
disposed of, otherwise, some minnows may
remain in the tank for several weeks. The
Odds and Ends
The Atlantic swallower heads the
list of fish remarkable for their eating.
It has such an expansive stomach
compared with its size, that it can
swallow fish larger than itself. The
stomach stretches until it is so thin it
becomes transparent.
The albatross has the longest wing-
spread of all birds, often 14 feet from
tip to tip.
The "call" of the tree toad is gen-
erally considered as a prophecy of
rain. Some truth in this, but not the
whole truth. Warm, moist air, which
usually precedes rain, releases the
male toad's mating urge, so he "sings."longer that fish are held in unnatural con-
ditions, the more susceptible they are to
fungus disease. When one batch of min-
nows has been sold, the tank should be
drained, cleaned and thoroughly sterilized
in sodium hypochlorite. The sides and bot-
tom of the tank should be scrubbed with
a solution of one-half pint of bleach (Hilex
or Chlorax) in 15 gallons of water. The
tank must be rinsed until all traces of the
bleach are gone before it can be refilled
for a new batch of fish. All tools and
dippers should be soaked in the hypochlo-
rite solution for several hours.
Though the methods outlined here will
keep fungus disease at a minimum, there
are times when the fish will become in-
fected in spite of good care. Minnows
that are infected or have been exposed to
fungus disease can be dipped in a solution
of one-eighth ounce of malachite green in
15 gallons of water for ten seconds. This
treatment is effective as a preventive or
as a cure. The solution loses its strength
in 24 hours and should not be saved. All
dead and dying fish should be disposed of
as soon as they are noticed. Dead fish
floating in the tank are a breeding grounds
for the fungus and, consequently, aid in
its spread.
Fish that are held for long periods of
time should be fed daily. Soybean meal,
finely ground oatmeal, or similar foods can
be used. The fish should be fed only the
food they will clean up in 15 minutes. An
excess will only pollute the tank and in-
crease the danger of fish loss.
Minnows in holding and transporting
tanks are living under very adverse condi-
tions. They have been handled roughly,
they have been crowded, and now they
are living without food in water that is
entirely lacking in natural disease prevent-
ives, so even under the best of conditions
they will have a hard time keeping alive.
The bait dealer can keep the loss at a
minimum by making the conditions as
favorable as possible. There is no magic
formula that can be used at this time.
There may be considerable loss from
the common practice of selling minnows
wholesale by the gallon. This procedure
necessitates the measuring of minnows in
a nearly dry state. It is impossible to
imagine that such measuring can be done
without injury to the fish. Minnesota
hatchery men weigh fish by first filling a
metal basket half full of water, weighing
the basket and water, and then adding
the fish and reweighing. The difference
in weight is the weight of the fish. By
counting the number of fish in a pound,
it is possible to determine the number
of fish sold. By this method it is possible
to wholesale fish by numbers, pounds, or
by gallons, allowing eight pounds to the
gallon. There is very little injury to the
fish during weighing.-Minnesota Conser-
vation Volunteer.JANUARY, 19489
7
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Texas. Game and Fish Commission. Texas Game and Fish, Volume 6, Number 2, January 1948, periodical, January 1948; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth1588331/m1/7/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.