Pretty Jawfish

Fish World | Pretty Jawfish | Jawfish belong to the family in the order Perciformes Opistognathidae. FishBase lists 60 species are currently divided into four genera: Lonchopisthus, Merogymnoides, and Opistognathus Stalix.

Physically similar to blennies, jawfish are generally smaller fish with an elongated body plan. Their heads, mouths and eyes are large in size compared to the rest of their body. Jawfish have a single, long dorsal fin with 9-12 spines and a tail that can be rounded or pointed. 

Jawfish typically live in burrows they construct in sandy substrate. They will stuff their mouths with sand and spit it out elsewhere, slowly creating a tunnel. Utilizing the protection of the caves, these fish feed on plankton float and other small organisms, ready to dart back in at the first sign of danger. They are territorial of the area around their burrows.
Jawfish are mouthbrooders meaning their eggs hatch in their mouths, where the newborn pups are protected from predators.

Different types of jawfish have been successfully kept by aquarists. It is important to use a suitable sandy substrate in the aquarium, these fish should be able to dig vertical burrows. Ideally, small pebbles, shell fragments and other types of naturally occurring elements. For example, three parts fine sand mixed with 1 part course material. The substrate in the tank should be at least 2-3 inches (5 to 7.5 cm) deep.
The jawfish will claim the vicinity of his cave as his territory. How much territory each fish will claim mainly depends on the species, some only a foot (30 cm) apart in the wild, while others of their holes at least 3.3 feet (1 meter) instead of each other.

The tunnel will arrange for a refuge and a drive to hunt plankton, which jawfish may arise and which they can retreat. Another function of the extended jaw is the man mouthbrooder, which means that the eggs hatch in the mouth, protecting the little offspring of predation and churning so they stay clean and aerated. Although the man left with all the parental duties, he is relieved after only 5 to 7 days, which is all the time it takes for the eggs hatch.
It is a non-aggressive fish that should not be kept in the same tank as aggressive species. You can combine such jawfish small, friendly non-aggressive fish and invertebrates.

Because jawfish tend to dig a lot, they can disrupt soil filters. If you absolutely want an undergravel filter, create a barrier between the filter and the top layer of sand. You can use eg mesh or glass fiber.