Like other deepwater fish,
Opisthoproctus soleatus needs to find its prey in a very dark environment, and avoid being detected itself by larger predators. Fishes with large upward-facing eyes likely hunt by detecting the silhouettes of prey above them which contrast with the low amounts of light coming in. While the exact purpose of this is unknown, it has been proposed that
O. soleatus uses this apparatus as a method of camouflage or to communicate with members of their species.
Diet Opisthoproctus soleatus has been found to primarily prey on bioluminescent
siphonophores; the bioluminescence of these organisms makes them more difficult to detect against the dim sunlight that filters through to the depths, but the structure of the lens and retina of
O. soleatus increases the optics and resolution of the eye, which allows them to detect the counter-illuminated animals.
Predation Opisthoproctus soleatus have been recovered from the stomachs of beaked whales (
Mesoplodon bidens) which had
beached themselves. Other species of Opisthoproctidae have also been found in the stomachs of
pygmy sperm whales and some
seabirds, such as
terns and
gulls. It has been proposed that the direction of emitted light from the rectal bulb and reflecting organ in the downwards direction decreases the chances of that light being detected by predators with forward-facing eyes. The larvae of
Opisthoproctus soleatus appear similar to adults, and have similar body proportions, though unlike the adults the larvae are pigmented, particularly at the base of the caudal fin and in between the pelvic fin and the anus. In larvae, the sole is silver, with two lines of black pigment increasing in size laterally towards anus. ==Conservation status==