Subject: A juvenile black Painted Frogfish (Antennarius pictus) has taken shelter next to a Blunt Arm Seastar (Pentaster obtusatus) on a sandy slope somewhere in the Bali Sea. In current-swept areas, it is not uncommon for different fish species to find refuge behind larger creatures that are much less affected by the current.
Frogfish are ambush predators that lure their victims into their reach. To do so, the frogfish has a lure (esca). This lure sits on top of a rod called the “illicium,” which the frogfish waves around. The lure attracts curious prey that, when coming too close, the frogfish will swallow whole. This way of catching prey is the fastest gape and suck mechanism in the animal kingdom; the process takes only 6 milliseconds. Sometimes, they catch a schooling fish so quickly that the other members of the same school don’t even realise one of them has been swallowed by the hungry frogfish. Knowing this, it is easy to understand why some people prefer to call them “anglerfish.”
Frogfish are also masters of camouflage. Their lumpy body can take the colour of any sponge in their vicinity over the course of a few days to several weeks, depending on the species. Once this happens, the frogfish is as good as invisible to the untrained eye and most fish.
However, frogfish are poor swimmers. Lacking a swim bladder, to move around they prefer to crawl on their pectoral fins. When they do swim, they are easily spotted by eventual frogfish predators. Frogfish are neither poisonous nor venomous and would make a nice meal for any piscivore on the reef.
Because they are terrible swimmers, they do not like the ocean’s current. Frogfish are therefore often spotted in the current-sheltered parts of the reef. Sometimes, as in this underwater videoclip, a juvenile Painted Frogfish uses the slow-moving Blunt Arm Seastar as a shield against the current on this sandy area. By doing so, the frogfish can travel distances without being exposed to the current of the Indonesian Throughflow that sweeps over the Balinese reefs and slopes. With a little luck, the opportunistic frogfish (they’ll eat anything that fits in their stomach) will be able to feed on other creatures that might also use this echinoderm as a protective shield against the current. Little cardinalfish sometimes take shelter against the current behind rocks, corals, and other available materials.
Technique: This is a typical example where it’s perfectly possible to put your underwater video camera on the bottom so that your images will be very stable. The little frogfish was a nice, unexpected find and a great underwater filming opportunity. I usually take a closer look when I come across any echinoderm on a scuba dive as they often host little and video-worthy critters, such as colourful shrimps, crabs with beautiful patterns, and even some mollusks like to take a ride on the back of these slow-moving, strange marine creatures. Some small animals live in symbiosis with starfish, sea cucumbers, feather stars, and urchins. So next time you come across one of these, move closer and take a good look; you might be surprised by what little treasures you can find.