SENSORY CONTRIBUTIONS TO NOCTURNAL PREY CAPTURE IN THE DWARF SCORPIONFISH (SCORPAENA-PAPILLOSUS)

Dwarf scorpion fish live in broken rocky reef areas at depths of 5-25m . By day they are found in crevices and beneath rock overhangs, wherea s at night they are observed sitting in the open. Gut samples show tha t feeding occurs predominantly at night with the most common prey item s being crabs and brittlestars. In the laboratory experiments, under a n artificial day/night light regime (LD 12:12) the prey species show a strong daily rhythm of activity, with activity confined to the period of darkness. Activity is controlled by light level. An artificial ''s unset'' in the middle of the day has both crabs and brittlestars emerg ing from cover at ambient light levels of about 4 x 10(-2) mu E.m(-2). s(-1) but not becoming fully active until dark. Under similar conditio ns, the dwarf scorpion fish's Visual threshold for response to a movin g visual target occurs at light levels of about 7 x 10(-3) mu E.m(-2). s(-1). Field measurements show light levels between these two values o ccur only for a limited period after sunset, and that light levels al night will probably be too low for visual feeding. The anterior latera l line system is described and its contribution to feeding shown in ex periments where fish in the dark, or blinded fish, precisely locate st ationary or moving crabs out to a range of about 10 cm. Particle strea k photography shows that the respiratory currents generated by the cra bs extend out to at least this range. Brittlestars ate most commonly t aken when they come into direct contact with the fish, particularly wi th the modified ventral edge of the pectoral fin. It is concluded that in the dwarf scorpion fish non-visual senses make an important contri bution to prey detection and capture.