Winter's Effect on Fish and Ponds
January 15, 2005
By Wally Hathaway, KHA
This morning, I awakened to 28 F and
rain. I eventually donned the hooded winter coat, gloves, and Sorrels in
order to venture out for a walk. Small icicles hung from the railings.
Footing was precarious. The tips of the fir branches drooped under the
weight of the glistening ice-really beautiful to gaze upon. In time, I
wandered near the pond's edge. Plants and ornamental grasses around the
pond were frozen stiff. As I slowly approached I could see my koi
hunkered motionless at the bottom. Reluctantly, I checked the water
temperature. (I didn't really want to know.) At the 1 foot level,
it was 39F. I slowly retreated to the warmth of the wood stove where I
could do a little reading. It is at times like this that I reach for
information by experts like Richard E. Carlson. REC has done a lot of
research on the effects of extremely cold temperature on koi and ponds.
One of the few things that most of us cannot
effectively control in our pond's ecology is the water temperature. The good
news is that Mother Nature has provided our fish with a natural ability to
adapt to the colder temperatures. This makes it our job to provide the best
environment possible and to duplicate what nature intended to happen in natural
waters. The bad news is that Nature has equally provided the other organisms in
our ponds the same survival mechanisms.
The first thing to consider when looking at
water temperature effects is to ask how cold our pond really gets. As pond
owners, we should know which temperature zone we live in and from this we can
determine the expected frost line depth in our soil. Local agriculture
extension services and most garden shops know this information, as do all
building inspectors. The importance of the frost line is that this is the depth
that the soil temperature will potentially reach 32 degrees F. Below this
depth, chances are that the soil temperature will remain at 35 degrees F or
above. Keep in mind that the soil around your pond will act
as a natural insulator and keep the water at the bottom of the pond at a
temperature above 35 degrees F. If you had the ability to measure soil
temperature at depths of twice the frost line, chances are you find that the
soil temperature does not drop below 40 degrees or so, thus providing a nice
natural insulator for our pond water.
Knowing the frost line depth should then be
a major factor when determining the depth of your new pond or whether or not
your fish can survive in your existing pond. As a general rule, the pond depth
should be at a minimum twice the depth of the frost line. For instance, if the
expected frost line depth is 12 inches, the minimum safe pond depth should be
24 inches below ground level. But these rules only apply to ponds built into
the ground and not for ponds built above the ground. For above-ground ponds,
the effects of cold air are remarkably more drastic, and cause thicker ice
coverings and lower temperatures
throughout the pond.
At 50 F and below, we are all too aware that
our biological filters have ceased to be effective against ammonia and nitrite
build-ups in our ponds. In fact, the fish are still producing ammonia through
respiration and what little food they are eating, mostly algae, so it is a good
practice to monitor ammonia and nitrite levels over the winter months.
Unlike ammonia, which has an immediate toxic
effect on fish, nitrite problems are caused by an accumulation of nitrites over
a period of time. Nitrites basically replace the O2 levels in the blood thus
causing "brown blood syndrome" and eventual death to the fish through
extreme O2 deprivation. So, it takes some time for koi to accumulate enough
nitrites to cause serious problems. How much time? That depends on a number of
critical factors including nitrite levels in the water, the chloride levels of
pond water, and the metabolism of the fish. In colder water (50 deg F and
under) we know that the fish's metabolism slows significantly and one of the
results is that the respiration will be less. This results in a decreased
opportunity to take up nitrites from the water. However, lethal levels of
nitrites can still be accumulated over time if the nitrite problem is not
addressed.
For most pond keepers facing nitrite levels during
cold water periods, salt is the best treatment as salt levels of only .1% will
inhibit the uptake of nitrites and prevent brown-blood syndrome. And, salt
levels of .1% can be maintained for indefinite periods of time without a risk
to the fish or concern for developing salt resistant parasites.
The next sets of organisms to discuss in the pond's
ecology are micro- and macro-organisms, more notably known as the parasites and
the bacteria. Here we will differentiate between the nitrifying bacteria and
the pathogenic bacteria that cause disease in our fish. Both of these bacteria
types are aerobic bacteria which simply means that they need oxygen to survive.
Most parasites are basically warm-water creatures and as the water temperatures
dip into the very low 50's and high 40's, the common micro- and macro-parasites
begin to die off in great numbers.
The lone exception to parasitic cold-water intolerance
is costia. Costia, which is formally named ichthyobodo necator and not to be
confused with common "ich", is one of the smallest ectoparasites
(lives on the outside) and is especially active in water down to about 38
degrees F. This is what makes it so dangerous to our fish during cold-water
times. As the fish's immune system and metabolic processes are reduced due to
decreasing temperatures, costia parasites are still active and have the
potential to cause significant damage through normal parasite attacks (cold
water ulcers) and increased stress on the fish. The good news is that costia is
easily managed through salt.
Like all living creatures, koi and goldfish can suffer
from hypothermia. Hypothermia occurs when the core body temperature becomes so
cold that normal body functions begin to fail. In human beings, this
temperature is about 93 deg F. For koi, this temperature depends on basically
two things: how cold the water gets and how fast the water gets cold. Koi are
poikilothermic, which means that their body temperatures are essentially the
same as the water temperature. And because of this, koi have no ability to
regulate their body temperatures. As the water temperatures drop, so does the
koi's body temperature and this affects the fish's immune system and
physiology. So it is pretty easy to see why water
temperature in a koi environment is so critical.
Hypothermia can become a factor when the pond water
drops below 39 degrees and really is a problem when it approaches 35 deg F or
lower. While all fish are susceptible to hypothermia, most fish do just fine
under normal cooling conditions, but there are some fish who just cannot handle
the cold. First evidence of hypothermia in fish is a loss in color followed by
rapid breathing/gill movement. Additionally, erratic swimming may occur that
looks like that the fish is disoriented. The affects of hypothermia can lead to
hypoxia, which basically means that the fish is starving for oxygen. While it
is true that cold water holds
more oxygen by its nature, because the fish's metabolism is so slow it cannot
adequately take up oxygen and suffers from low oxygen affects. Hypoxia can then
lead to anemia and this puts the fish in a serious position. Reversing the
conditions of hypothermia requires that the fish be removed to a tank that can
be warmed slowly. No matter how hard we try to keep things perfect, too often
something goes wrong and our fish need some first aid. There are some
tricks to successfully treating fish in cold water/cold weather
environments.
1. Try to keep the fish in the same
temperature water to which he is acclimated. Many well-meaning fish owners will
put the fish in warmer water thinking this will help, when in fact this will
most likely kill the fish. Koi can only handle a temperature change of 10
degrees at a time. Plus, fish "know" their water and by keeping them
in water they know will reduce some of the stress. A good trick is to perform
pond-side treatments with a quick release back to the pond. It worked well for
me. I had 2 koi with the start of an ulcer. They were each netted twice
for treatment at pond side with Neocide. They have no further evidence of
ulceration.
2. If the
decision is to bring the fish indoors, plan on keeping him inside until spring.
Too many ecological changes will do more harm than good. When the fish is
brought inside, use pond water in the largest container you can handle and let
the water warm "naturally" until it hits room temperature. The longer
it takes to
warm, the better. A little ice can help to slow down the process monitor the
water temperature and allow no more than a 1 degree temperature change per
hour, and no more than 5 degrees in 12 hours.
3.If the
fish needs to be netted, do so as gently as possible. Netting adds to the
stress of the fish coupled with cold water and parasites/ infections, only
compounds the problem. Pond-side salt dips for parasites (.6% for 30 minutes or
less) should be done using pond water in a large container and with some effort
at reducing the effects of the cold air.
Curing bacterial infections is a tricky business in warm
water, let alone in cold water when the fish has no functioning immune system
to speak of. If you are seeing ulcers or fin rot, your only course of
action may be to bring the fish indoors to a q-tank for the winter. If
you plan to return the fish to the pond, then you will have to reverse the
procedure you used to get the fish warm. My experience with cooling is
limited, but I must confess that the result was dismal.
The consistent theme is to duplicate Mother Nature
whenever possible. In natural waters, the water supply is replenished by
springs and rivers and the fish are treated continually to refreshed water.
In our ponds, we have to perform this act routinely to ensure that the
environment and ecology stay balanced.This is why we do water changes and water
quality tests. This is our best attempt at duplicating Nature.