|
|
Do fish “Hibernate”?
The vast majority of pond
fish such as goldfish, koi, comets, shubunkins and orfe, are
related to the carp and has been over wintering in our
climate successfully for years.
Fish are cold blooded,
which means that they take their body temperature from that
of the surrounding environment. When it is warm, they are
active, feeding, growing, and producing waste. The reverse
is true as the water temperature declines. As long as the
drop in water temperature is gradual, lagging slightly
behind the reducing air temperature, then fish adapt to what
for them is quite a natural phenomenon. They respond to
cooling water by a drop in metabolic activity. Thus their
caloric demands decline and their digestion slows. This is
why it is imperative to monitor outside temperatures when
feeding fish, gradually decreasing the amount as the
temperature falls, and switching to more easily digestible
food such as wheat germ, to minimize digestive issues from
the fish having more food in the intestines than it has the
energy to process.
A carp’s physiology is
geared to over wintering and this physiology has been
inherited by their ornamental cousins. The shortening day
length as winter approaches causes pond fish to prepare for
winter before it arrives, feeding in excess when possible to
store sufficient energy to survive the winter. Although
winter may come as a shock to humans, pond fish have been
preparing for this change for months.
As soon as the water
temperature drops below 50 degrees Fahrenheit, fish become
relatively inactive, settle to the bottom of the ponds, and
should not be fed again until the temperature rises about 50
degree in the spring. They are actually not hibernating but
are awake and will move if startled, although slower that
usual. The fish are more susceptible to disease in lower
temperatures due to a less efficient immune system. It is
important that the ponds has been cleaned prior to winter,
is not overcrowded, and that there are no pre-existing
diseases such as parasites on the fish. Chilodonella can
reproduce in cold water and is an especially important
parasite during winter months.
Other points to remember
are to always have mild surface water agitation to keep the
pond from freezing over completely. Fish require a hole in
the surface of the ice for gas exchange, however, do not
hammer at the ice and disturb the fish’s slumber and
increase their metabolic demands. Cold water hold more
oxygen than warm water, so waterfalls and fountains are not
necessary for oxygenation if there is no overcrowding.
Filtrations should be adjusted to not disturb the water at
the bottom of the pond. Dense water that settles on the
bottom of the pond, mixed with the colder water at the
surface will chill and can cause the fish to freeze. The
exception are ponds which are heavily planted with submerged
aquatic plants that consume oxygen under the ice, in this
case supplemental oxygen is necessary to avoid “winterkill”.
Of course pond fish can
always be brought indoors in the winter, or the pond can be
heated to facilitate year round activity, growth, and to
prevent winter stress. Heating outdoor ponds can be quite
costly, and the bacteria in the biofilter must also be at a
high enough temperature to process nitrogenous wastes.
In summary,
fish do not truly hibernate, but are well adapted to adjust
to cold temperatures. With a little thoughtful planning,
they slumber peacefully waiting for spring to return,
looking forward to the opportunity to bond with us again! |
|
|
