They are known to feed mostly on crustaceans (as well as other invertebrates) and small fishes, which include juveniles of their own species. Pterois volitans consumes an average of 8.2 times its body weight per year. As juveniles they consume 5.5-13.5 g per day and 14.6 g a day as adults.
Sunset is an optimal time for Pterois volitans to begin feeding because this is when activity in the coral reef is highest. At sunset, all of the day fish and invertebrates make their way to a resting spot for the night and all of the night fish come out to begin feeding. With all of these creatures around, the lionfish need not invest much energy to find a meal. They simply glide upwards along the rock and coral sneaking up on unexpecting prey from below. While moving slowly towards a small fish, Pterois volitans uses its open pectoral rays to shield the motion of its caudal fin. This shielding along with the cryptic coloration of the predator prevents the prey from becoming alarmed. Although we find the striped colorful pattern of the lionfish obvious and easy to see in an aquarium setting, in the coral reef this colorful pattern allows the fish to blend into the background of coral branches, feather-stars, and spiny sea urchins.
The lionfish attacks with one swift gulping motion that sucks the prey into its mouth. This attack is so quick and smooth that if the victim is among a group of fish, the other fish in the group may not even notice what happened. The lionfish can continue to hunt the other unaware members of the group.
Pterois volitans has also been known to hunt for fish in the open water near the surface with a different technique. Here they wait 20-30 cm below the surface and watch for small schools of fish leaping out of the water in an attempt to escape another predator. When they plunge back into the water the lionfish is waiting just below them ready to attack
In addition to fish, Pterois volitans feed on invertebrates such as amphipods, isopods, and other crustaceans. The lionfish glides along the substrate (rocks or sand) and vibrates the rays on its fins in order the rustle the food out of hiding.
In general, the lionfish is stationary and feeds on as many fish as it can when fish are plentiful and then it fasts when food is scarce. When a lot of food is available for feeding, Pterois volitans becomes satiated or full and may not eat for at least 24 hours.
Lionfish invest most of their energy in growing to a large body size early in life. This tactic allows them to grow big at a fairly young age so that they are more likely to avoid attack by predators and increase their chances of mating successfully
If a male lionfish meets another male while hunting, the more aggressive male will turn darker in color and point its poisonous, spiny dorsal fins at the other individual who usually folds down its pectoral fins and swims away.
Pterois volitans is not currently listed as threatened or endangered. However, the increase in pollution in coral reefs is expected to kill many of the fish and crustaceans, which lionfish depend on. If lionfish are unable to adjust to these changes by selecting alternate food sources, it is expected that their populations will also decrease