Abstract:
Dwarf scorpion fish live in broken rocky reef areas at depths of 5–25 m. By day they are found in crevices and beneath rock overhangs, whereas at night they are observed sitting in the open. Gut samples show that feeding occurs predominantly at night with the most common prey items being crabs and brittlestars. In the laboratory experiments, under an 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 “sunset”; in the middle of the day has both crabs and brittlestars emerging from cover at ambient light levels of about 4 × 10‐2μE.m‐2.s‐1 but not becoming fully active until dark. Under similar conditions, the dwarf scorpion fish's visual threshold for response to a moving visual target occurs at light levels of about 7 × 10‐3μE.m‐2.s‐1. Field measurements show light levels between these two values occur only for a limited period after sunset, and that light levels at night will probably be too low for visual feeding. The anterior lateral line system is described and its contribution to feeding shown in experiments where fish in the dark, or blinded fish, precisely locate stationary or moving crabs out to a range of about 10 cm. Particle streak photography shows that the respiratory currents generated by the crabs extend out to at least this range. Brittlestars are most commonly taken when they come into direct contact with the fish, particularly with the modified ventral edge of the pectoral fin. It is concluded that in the dwarf scorpion fish non‐visual senses make an important contribution to prey detection and capture.
