According to Ray, water temperature, wind direction, barometric pressure, light conditions and even the moon’s phases have a bearing on fish behaviour and appetite. If you aren’t able to pick the best conditions for your fishing, you can still choose tactics to suit the conditions and, therefore, the fishes’ mood – so improving your chances of success on the day.
Fish are cold-blooded – taking on the temperature of their surroundings — and, as a very general guide, they tend to be more active when the water is moderately warm rather than extremely warm or cold. At low temperatures – under 6°C (42°F), say -they become inactive and at times lie dormant on or near the bottom and are reluctant to feed. When the temperature rises above about 25°C/77°F (depending on the oxygen content) – they again become inactive but, rather than hugging the bottom, many species tend to rise in the water. For example, on really hot days you can often see carp and chub basking just beneath the surface.
Small fish are affected less by water temperature. Bleak, for example, often feed in very cold water when larger species like chub, barbel or bream won’t – useful to know if you are fishing a match on a winter river because it may influence your tactics. Indeed, if you don’t mind catching very small fish, a respectable bag of roach, perch, gudgeon or bleak can often be taken regardless of the water temperature. It’s a good idea, therefore, to carry a water thermometer along with your other gear. Changes in temperature are the most critical – a sudden drop in temperature being the angler’s worst enemy. Even during the summer an influx of cold water can cause water temperature to drop by a few degrees and kill sport stone dead. In winter a cold snap produced by a severe overnight frost can leave you wondering whether there are any fish in a water.
Apart from rivers like the Trent (which is affected by warm water pumped in from bank-side power stations) it usually takes much longer for a water to heat up than it does to cool down. But in winter even a slight rise in temperature can result in bumper catches – especially if it follows a freeze. At this time of the year, it is a good idea to look for swims with features which that the latter outfishes the former. On still waters a steady breeze often blows leaves, dead insects and other debris across the surface, causing it all to accumulate in thick scum along one bank. This may look unsavoury to us but to the fish it provides a well-stocked larder of wholesome morsels. Areas such as these are well worth the angler’s attention.
Keep an eye on the barometer too. Given a reasonable water temperature, a level pressure usually means fair sport but sudden changes – particularly down – can mean poor returns.
Some anglers favour overcast rather than bright days – the theory being that fish can’t see them so well when it is dull. This is more important when the water is clear – as is often the case in late autumn and winter. Under these conditions bankside disturbance can affect the fish – especially if the water is shallow. In summer, waters are often highly coloured because of algal bloom and unless fish are feeding very close in or near the surface, clear skies and bright sunlight are not really a problem for the angler.