Do Fish Freeze in Winter?

THE FROG BLOG

Do Fish Freeze in Winter?

The Vertex aerator in this pond keeps an area of open water in
the ice and provides needed oxygen for the fish below.
Photo by John Wilson

The winter of 2013-14 has, thus far, proven to be a harsh one.  The extreme cold temperatures have caused many freshwater lakes and ponds to completely ice over and the blanket of snow has blocked out the light.  So what happens to the fish?  Do they freeze?  Do they hibernate?  Freshwater fish have adapted to all manner of harsh climates and the way in which they survive varies from species to species.  Many fish thrive in the frozen ponds, whereas others enter a state of near hibernation.

Fish are coldblooded creatures, or poikilotherms.  Coldblooded animals do not have the ability to warm themselves and their body temperature is regulated by their surroundings.  In other words, the body temperature of a fish will be close to that of the surrounding water.  Different species of fish have different tolerance to temperatures and are categorized as coldwater, coolwater and warmwater.  The fish will go to the area of the water most suited to their cold tolerance.  Fish with a higher cold tolerance will be more active, where as those with a lower cold water tolerance will be less active.

In the summer time, the warmer water is closer to the surface.  However, in winter, it is the exact opposite.  The colder water rises toward the surface and the warmer water sinks to the bottom.  Fish with low tolerance for cold, such as largemouth bass will seek out sheltered areas at the deeper depths and will not move much.  These fish enter a state near hibernation.  They will be sluggish and seem to hang suspended in the water and some species burrow into the bottom.  Their need for food drops considerably and they need very little to survive.  In fact, the metabolism of a fish in this state will be such that it may take up to a week for food to digest.  Fish with a higher cold tolerance, such as trout, will be more active and remain near the surface.  The cold temperatures do not cause the dramatic changes in activity in these species.  Coldwater fish will keep feeding regularly and move to warmer waters as the food supply dwindles.

Problems can arise for many fish species when the temperatures are so extreme the water freezes over completely.  When this happens, and especially when a blanket of snow blocks out the light, the oxygen levels can drop severely.  The fish will seek out areas of greater oxygen concentration.  However, if the oxygen levels drop too far, a winter fish-kill can occur.  Some fish loss is to be expected.  Fortunately, however, a large scale winter fish-kill is not a common occurrence, but it can happen.  The risk of a large fish-kill can be mitigated by keeping oxygen in the water through use of a bubbler type aerator with bottom diffusers, such as the Vertex systems.  Bottom bubbler diffusers will also keep an area of open water in the ice to allow for gas exchange.

Nature has the incredible ability to take care of itself.  Animals adapt and fish are no exception.  Yes, fish can succumb to harsh winters, but most will make it through just fine.  However, in harsh conditions like we are currently seeing across the country, the pond owner can help their fish survive by keeping oxygen in the water.  If you would like further information on keeping your waters and fish healthy and/or bottom aeration systems, call us for a free consultation with one of our Aquatic Specialists. 

Stay warm and here's to open waters!

~The Frogger Blogger



Sources:

http://www.redorbit.com/news/science/1175593/how_freshwater_fish_survive_the_winter/

http://dnr.wi.gov/wnrmag/2009/12/ice.htm

http://www.hngnews.com/lake_mills_leader/news/local/article_d2c9824e-9726-11e2-845b-001a4bcf6878.html?mode=print