Winter can be a very tough time of year for your pond fish outside. And its very easy to temporarily forget about your fish outside as they become dormant and require less of your time. But winter is still an important time for your fish and you need to keep an eye on them to check that they are fit and healthy enough to cope with the extra stress that freezing temperatures can bring.
Pre-Winter
Preparation is the key! Before the temperature starts to drop and we start to get frosts you should check that all your fish are healthy and well fed. Fat reserves will be used up during the cold winter months so be sure that all your fish are feeding well over the last few summer months. Treating your fish with an all round treatment such as Tetra's Medifin is a good idea. Do this before the water temps drop too low as most medications will not be as effective.
Winter Arrives
When the first cold spells start to arrive it is very important to feed your fish a wheatgerm food. This is a specially formulated food that fish can easily eat and digest during colder temperatures. You can feed your fish wheatgerm food all winter if they are actively feeding (over a mild winter).
If in the coldest of winters your pond should freeze over completely, don't panic too much. Fish can survive a short while on the absorbed oxygen levels in the water (which is higher in colder water). Importantly do not smash the ice. All fish are extremely sensitive to vibrations and water pressure. Smashing ice on the pond can stun and kill your fish. Ideally leave something in your pond to keep an area ice free over night or gently melt an area of ice in the morning.
Now is the time that you should really keep a close eye on your fish for signs of disease. Now the water temperature has dropped so has your fish' immune system and defence against disease and parasites. Look for any abnormalities on the fishs skin and scales. White dots, red patches and red streaks imparticular.
Also look out for any out of the ordinary behaviour. Unusual swimming patterns are a very good indicator that something is wrong. If one fish separates itself from the others this usually means that something is wrong.