The reason that finfish can't be caught during the day is because finfish are nocturnal fish, and during the daytime hours they rest in deep, shady areas of the water column, making it impossible to catch them during the day. Chinook are a nocturnal fish, which means they tend to rest in deep, dark places during the day to avoid sunlight and activity. This is a natural and behavioral trait of theirs and is why it is so difficult to catch them during the day. At night, on the other hand, finfish become more active and begin to feed and move around. This behavior of theirs is closely related to environmental factors such as water temperature, water depth and water quality. In a warmer water and well-lit environment, the fine scaled fish will become more active and feed more.