Ambient Weather DHR70B-BRASS Handheld Fishing Barometer Tide, water temperature, light level and moon phase can affect fishing success. Barometric pressure also has a major influence on fish behavior. The Ambient Weather Fishing Barometer displays ranges of pressure that are great (green), good (blue) and poor (orange) for fishing conditions with the color coded scale. A fish senses pressure changes through its air bladder. Fish that have small air bladders, such as kings, Spanish mackerel, wahoo and dolphin, aren't as affected by barometric changes as those with large bladders, such as trout, redfish, tarpon, grouper and snapper. When their bladders expand, fish become uncomfortable. They relieve their discomfort by moving lower in the water column or by absorbing extra gas in their bladders. Note: Barometer only operates to 3,000'. Do not order this item if you live at or above 3,000'.