Fig. 4

ONT eyeshine excitation efficiency and light path in T. delaisi. a Excitation map showing area where ONT eyeshine can be induced by dorsal illumination with small light spots (ca. 1 mm²). Dot size corresponds with perceived intensity of ONT eyeshine in the right eye. b Reversing the light path, i.e., shining light through the (left) pupil of a recently sacrificed fish, produces glow corresponding to the maximum excitation field just behind the eye (compare a). Position of glass fibre is shown as solid line, head contour as dashed line. c Aiming the glass fibre light at the snout makes most of the head glow, except for the eyes. d Schematic of T. delaisi’s head in dorsal view. The black dots represent the positions of ONT eyeshine excitation, the result of which is shown in e). LOT/ROT left/right optic tectum, LTE/RTE left/right half of telencephalon, LON/RON left/right optic nerve, ONTE optic-nerve-transmitted eyeshine. e ONT eyeshine intensity in the right eye of a recently sacrificed T. delaisi with dorsal cranium removed. The tip of a single glass fibre was placed over different brain areas, as specified in d). The images show the correspondent ONT eyeshine emerging in the right eye. Numbers indicate pupil mean grey value as a proxy for ONT eyeshine brightness. All images were taken with a DSLR camera and identical settings