Fish are pecilothermic (body temperature varies depending on ambient temperature), water temperature variations (even if reduced) can move the fish to areas where they feel more comfortable. Temperature receptors on the body surface of fish usually detect temperature differences in the order of 0.1°C to 0.03°C.
When the temperature of the water decreases, some species simply stop eating by reducing their body activity (swim less, sometimes stay in a semi-conscious state, do not feed). One of the ways that fish have to counteract this temperature variation is to go down or climb in depth. The temperature of the water differs greatly from the ambient temperature, the proximity and type of coast. Is the thermometer an indispensable tool? The knowledge of the species and its habits is fundamental, the fisherman’s experience teaches that in certain waters there is one species or another, but none of us have the notion of the water temperature at 20 meters depth, know the temperature of the water It becomes a useful tool in the definition of the fishery and the species to be captured avoiding two or three hours of fishing in a certain place that, by the temperature of the water, that species can not be. The water temperature, in most cases, decreases as the depth increases.Large water bodies (dams, lakes) present stratification, with layers having different temperatures and dissolved oxygen levels implying a differentiated distribution of species in depth. There are fish that feel better in colder waters (trout 15 to 17ºC), others of tropical and subtropical species in much warmer waters (Golden 25ºC, Pácu 26ºC) and still others where the thermal comfort margin is more Wide (achigã=black-bass, corvina).
The temperature of the water is influenced by the sun by directly contacting nearby rocks, which absorbed solar energy during the day, by entering inland waters (river mouths), standing waters (bays, coves). The zones of encounter between waters of different temperatures, are zones where fish is common, the base explanation is that in these zones there is a zone near where the temperature of comfort is the most adequate. Locations with submerged rocks, locations with inlets, riverbanks, harbor ports are usually ideal locations for surface fishing.