They lack haemoglobin in their blood, resulting in their blood being colourless. One Channichthyidae species, the mackerel icefish (Champsocephalus gunnari), was once the most common fish in coastal waters less than 400 metres (1,312 ft) deep, but was overfished in the 1970s and 1980s. Schools of icefish spend the day at the seafloor and the night higher in the water column eating plankton and smaller fish.[13]