Engineer Goby

The engineer goby is a fish that lives up to its name with its long, snake-like body and its habit of constantly digging in the sand. Although its name includes "goby" (or "blenny" in some English names), it is neither; it belongs to the family Pholidichthyidae, which has only two species. Juveniles, with a single white stripe running along their jet-black bodies, mimic the juveniles of the venomous striped eel catfish (Plotosus lineatus). As they grow, this neat stripe breaks up; adults develop a pattern of white spots or broken bands on a black-brown background.

It is sold in stores as juveniles of 5–8 cm, but in the wild it can exceed 30 cm. It grows slowly in the aquarium; still, take its adult size into account when buying. It is very hardy and accepts almost any food. All day long it carries sand out from under the rocks; this behavior can topple rock structures that are not built securely enough.

It lives in shallow lagoons and coastal reefs of the western Pacific, from the Philippines to the Solomon Islands, mostly at depths of 10–20 meters. Juveniles form tight schools under rock overhangs and around coral heads; the school swims so closely that it looks like a single large animal. Adults are more secretive and live in tunnel systems under the rocks.

• Volume: at least 300 liters because of its adult size; juveniles can start in a smaller aquarium but must be moved as they grow.
• Water: salinity 1.023–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C; it is sensitive to ammonia and nitrite.
• Substrate: a deep sand bed (8–10 cm). Build the rock structure before adding sand, setting it directly on the glass; it hollows out the area under the rocks.
• Corals: corals placed on the sand or on low rocks may get buried in sand; glue corals securely in high spots.
• Lid: juveniles can escape through small openings; a lid is essential.
• Reef compatibility: it does not eat corals. It generally leaves shrimp and fish alone; still, do not keep it with very small creatures that would fit in a large adult's mouth.

Carnivorous. It readily accepts frozen mysis, brine shrimp, krill, finely chopped seafood and sinking granules. Feed juveniles 2–3 times a day and adults 1–2 times a day. It usually snatches food from the mouth of its tunnel.

Peaceful and shy; it spends most of the day in its tunnels and becomes more visible in the evening and at feeding times. It can be quarrelsome toward its own species, but juveniles that grow up together are usually compatible. When startled it retreats into its burrow.

Good companions: tangs, dwarf angelfish, clownfish, damsels, wrasses, foxface, cleaner shrimp.

Avoid: tough, large fish such as triggerfish; bottom corals that would be affected by its digging, and sand-sifting gobies.

It can be kept singly; in a large aquarium a small group of 2–3 juveniles added at the same time will also live together. In adulthood, pairs may become distinct within the group. Do not add unfamiliar fish to the group later.

It lays its eggs inside the tunnel system and guards them in the burrow. The fry leave the burrow and roam in a school during the day. Breeding has been observed very rarely in the aquarium.

• Very hardy; keep new fish in quarantine for 3–4 weeks.
• It is sensitive to rising ammonia and nitrite; stable water values are important.
• Escaping and getting trapped under rocks are the most common causes of loss.

No reliable external difference is known.