This chapter addresses only injury-released cues in distressed fish. It presents the discussion of the skin glands in nonostariophysan species. In fishes, one method of early detection of predators is through chemical alarm cues. The family Salmonidae probably contains the most economically important species that have been tested for alarm chemicals. Alarm chemicals also can influence the survival of salmonids indirectly. Environmental pollutants may inhibit the ability of salmonids to detect or recognise salmonid alarm cues. The question of whether the alarm chemical is homologous within some or all of the live-bearing fishes has not been well studied. The best-studied species of stickleback with respect to chemical alarm cues is the brook stickleback, Culaea inconstans. Only a few species of sculpins have been tested for potential responses to alarm chemicals. Overall, few marine species have been tested for the presence of alarm chemicals.