Behavioral responses of two deep-sea fish species to red, far-red, and white light

Abstract

The relatively unobtrusive deep-sea camera system Eye-in-the-Sea (EITS) was deployed in Monterey Bay Canyon, California, USA, to assess the relative photosensitivity of 2 deep- sea fishes, Coryphaenoides acrolepis and Anoplopoma fimbria. Previous studies addressing the in situ response of deep-sea fishes to red and white light were done in the presence of ROV-induced stimuli. Here, we report on the behavioral response of C. acrolepis and A. fimbria in a vehicle-free environment when subjected to white (full visible spectrum), red (685 nm), and far-red (695 nm) illu- mination in situ. Under far-red light conditions, A. fimbria spent significantly more time in the field- of-view and demonstrated an increase in entrances/exits when compared to the situation under red-light and white-light conditions. No significant difference in the average time C. acrolepis spent in the field-of-view was found between any of the test wavelengths; however, the entrances-to-exits ratio for C. acrolepis decreased during white-light conditions. While A. fimbria often displayed a flight response at the onset of white and sometimes red (685 nm) illumination, C. acrolepis did not demonstrate a similar behavioral response when exposed to light within its range of visual sensitiv- ity. A. fimbria undergo a dramatic ontogenic shift in depth, inhabiting well-lit, near-shore waters as juveniles and moving into deeper waters as adults. It is thought that C. acrolepis spend part of their early life history in the light-limited mesopelagic, below the permanent thermocline, and move into deeper waters as they mature. Based on the results of the present study, we hypothesize that systematic differences in the phototactic responses of deep-sea fishes are a function of life history as well as spectral sensitivity.