The Sargassum frogfish (Histrio histrio) is an example of perfect adaptation. It is a species of frogfish that is only found living among the floating algae of the genus Sargassum. Sargassum algae forms rafts that float about the ocean’s surface and provides a unique habitat for some specialized fish, as well as a refuge for the young of some open-ocean species. The Sargassum frogfish hitches a ride on this botanical craft, feeding opportunistically on other animals that use it as a home. While recreating a Sargassum microhabitat in the home aquarium is next to impossible (the algae is rarely available to aquarists), this fish can handle living in an aqaurium without it.
Difficulty: The Sargassum frogfish is not difficult to keep. Feed the Sargassum frogfish marine fish and crustacean flesh to ensure that it receives all the fatty acids and other nutrients required to stay healthy. You can try and entice your Sargassum frogfish to feed off a feeding stick (use a rigid piece of airline tubing with one end sharpened). Be aware that you should never feed Sargassum frogfish large prey items (i.e., items that are up to half the length of the fish). If one of these fish eats something too large (including fish tankmates), the food item may decompose faster than the Sargassum frogfish can digest it. This can result in the Sargassum frogfish collecting gas in the alimentary tract, which will cause it to float like a buoy. In most cases, the Sargassum frogfish suffering from this malady will perish. Feed the Sargassum frogfish several times a week.
Physical description: The Sargassum frogfish is easy to recognize. The Sargassum frogfish is pale yellow to orangish-brown with numerous darker spots and squiggly lines. The Sargassum frogfish’s skin is covered with dermal flaps, which enable it to blend in even better (these markings sometimes fade, and the dermal appendages may be fewer in number or even disappear, depending on the environment). The Sargassum frogfish can reach a length of 7.5 inches. The Sargassum frogfish is sometimes confused with the hispid frogfish (Antennarius hispidus) in the aquarium trade. The Sargassum frogfish can be differentiated by the fishing rod and lure: H. histrio has a small illicium (rod) without a lure (esca), while A. hispidus has a well-developed illicium and a fuzzy, pom-pom-like esca.
Range: The Sargassum frogfish is found in tropical seas worldwide. The Sargassum frogfish is usually found at the ocean surface, but has also been reported at a depth of an incredible 1,900 feet (the larvae and post larval fish up to a length of about 4 mm are the ones that are sometimes found at great depth).
Compatibility: The Sargassum frogfish will eat any fish or crustaceans it can swallow whole. What makes the Sargassum frogfish even more lethal is that it has a huge mouth and flexible stomach that enable it to ingest fish longer than itself. The Sargassum frogfish is best-kept on its own or with larger fish, but avoid species that graze on corals, sponges or tunicates. Fish that feed on encrusting invertebrates (e.g., butterflyfish, angelfish, triggerfish, filefish, pufferfish, porcupinefish) may mistake the skin of the Sargassum frogfish for food-ridden substrate and persistently nip at the sedentary fish. The Sargassum frogfish can be housed with other predator fish, such as scorpionfish, hawkfish, groupers and snappers, as long as they are too big to swallow. The Sargassum frogfish should not be kept with members of its own kind, unless you can acquire a male Sargassum frogfish and female Sargassum frogfish. (Note: pair members may actually even fight with one another when not in reproductive conditions.) The Sargassum frogfish is cannibalistic — one wild-caught specimen contained 12 smaller H. histrio.
Aquarium conditions: Histrio histrio can be kept in an aquarium as small as 10 gallons. If you want to try and recreate its natural habitat, place a floating mass of Caulerpa in your aquarium. The Sargassum frogfish will also hide among the blades of macroalgae that are attached to the substrate. Keep the water parameters for the Sargassum frogfish as follows: pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 72 to 82.
Care considerations: While the Sargassum frogfish does not look aerodynamic, the Sargassum frogfish can flip out of open aquariums. Apparently, this ability enables the Sargassum frogfish to flip around on the algal mat. Be careful when removing the Sargassum frogfish from the aquarium, as it might ingest air when out of the water. If the Sargassum frogfish does, it may have a difficult time releasing the air and eventually perish. It is best to keep the Sargassum frogfish submerged when moving the fish from one aquarium to another. The Sargassum frogfish is very susceptible to parasites.
Breeding: The Sargassum frogfish will spawn in captivity. The female Sargassum frogfish lays an egg raft, which is a ribbonlike matrix permeated with the eggs. It will break apart, and the eggs will hatch in four or five days. At hatching, the larvae are around 1.4 mm in length, and the yolk sac disappears at 11 days of age.