Marine fish come in a dizzying array of shapes and colors. Unfortunately, many of the oddest looking fish are delicate, expensive, or both delicate and expensive.
But not always. The Engineer Goby is an excellent beginner’s fish that isn’t nearly as popular as it should be. Unusual in habit but outgoing and peaceful, these are fascinating saltwater fish that deserve a place in any community tank!
What is the Engineer Goby?
Engineer Gobies go by a few names, including Convict Goby and Convict Blenny. This adds to the confusion in identifying these amazing fish because there is another fish that also goes by the name Convict Blenny, Priolepis nocturna. And this fish actually happens to be a true Goby.
Engineer Gobies are actually members of their own family, Pholidichthyidae. And interestingly enough, they are closely related to the almost entirely freshwater Cichlidae family, which includes Angelfish, Oscars, and other popular aquarium fish!
Like most Cichlids, Engineer Gobies are carnivores that feed on anything small enough to be overpowered and eaten. While they are peaceful they are a threat to smaller tank mates, especially small, thin fish.
And like Cichlids, Engineer Gobies are sociable and slightly territorial. They rarely squabble among themselves, however. Groups of Engineer Gobies form colonies of dozens or even hundreds of individuals in the wild that work together to form interconnecting tunnels many meters long.
This constant construction habit is what gives the Engineer Goby their most common name. These fish simply aren’t comfortable unless they have structures to burrow under. When young they are a solid black with a silvery white stripe. They look quite a bit like the mildly venomous Coral Catfish (Phetusus angularis).
As they age the horizontal stripes meld into blotches and finally vertical bars and the Engineer Gobies spend less time swimming exposed.
While they aren’t especially rare there is very little information out there on these striking fish. So let’s dive into how to care for these “gobies!”
- Common Names: Engineer Goby, Convict Goby, Convict Blenny
- Scientific Name: Pholidichthys leucotaenia
- Origin: IndoPacific; Indonesia, Fiji
- Length: 12 inches
- Aquarium Size: 55 gallons
- Temperament: Peaceful; Social
- Ease of Care: Easy
Engineer Goby Care
Overall, Engineer Gobies are easy to care for. They are hardy, eager eaters, and not too big. However, there are a few concerns that we will address below!
Aquarium Size
The Engineer Goby typically reaches a maximum size of 12 inches in home aquariums but sometimes grows larger in the wild or with extreme age. They are known to reach 11 years of age and up to 18 inches but this is very rare.
Therefore a 55 gallon aquarium is an absolute minimum for adults. Young Engineer Gobies (2-3 inches) can be kept in smaller tanks (20+ gallons) until they mature. Being carnivores with a methodical way of eating, larger water volumes are recommended.
Smaller tanks shift in parameters very quickly and a single overfeeding event can cause drastic shifts in ammonia and nitrite.
Be aware that like many eel-shaped fish, the Engineer Goby is an escape-artist in training. Especially when young, which is when they spend more time free swimming. At night your Engineer Goby may try testing the bounds of the tank.
Loose lids or holes for pipes and wiring are all possible escape routes for these busy fish. So make sure the tank is well secured to avoid a sad discovery the next morning.
Water Conditions
Engineer Gobies are one of the more beginner friendly marine fish. They don’t have specific requirements in the way of water conditions and prefer standard marine parameters.
Temperatures should be a little elevated. You want to keep them between 75-82℉ as their native range is around equatorial island groups such as Indonesia. And while you want to keep ammonia, nitrite, and nitrate as close to 0ppm as possible, Engineer Gobies aren’t especially sensitive to slight amounts of these compounds.
What is important is to make sure that your water is free of high bacteria/fungal concentrations. The Engineer Goby is a scaleless fish and worse, a digger. Scaleless fish lack the protection offered by hard scales. Wounds caused by fighting, predators…Or scrapes from digging…Are very prone to getting infected.
An Engineer Goby can easily get a scratch from a coral frag if it suddenly dashes back to its burrow in a panic for some reason. And if the water has higher than normal concentrations of bacteria, fungi, viruses, etc, due to poor parameters…Infections are likely to come up.
Worse, scaleless fish are highly sensitive to medication doses. Fish scales slow the uptake of medicines normally. When treating scaleless fish, it’s better to use ½ of the usual dose unless you’ve treated these fish before for the same agent.
Of course, ½ dose might not be enough to treat the infections. Or you may need more time than normal for the disease to run its course. Either way, a quarantine tank is the way to go for dealing with a sick Engineer Goby.
Water Conditions for Engineer Gobies:
- Temperature: 75-82℉
- pH: 8.0-8.4
- Specific Gravity: 1.020-1.025
- Alkalinity: 8-11 DKH
- Ammonia, Nitrite, Nitrate: As close to 0ppm as possible
Aquascaping for Engineer Gobies
If you decide to buy an Engineer Goby you’ll need to put a little extra thought into how you lay out your tank. They get their name from their habit of building huge tunnels under and throughout coral rubble. And they aren’t exactly small fish.
They can move up to 6 lbs of sand a day in nature once they decide they want to dig a deep tunnel! And these tunnels can be many meters long.
Unfortunately, it’s common for an Engineer Goby to get trapped and die in reef tanks. Coral rubble can shift suddenly, pinning the Goby in place until it starves. Worse, these fish like to disappear for days or even weeks on end. You may not even realize it trapped itself until it’s much too late.
So your aquascape needs to be secure enough to withstand some undermining and jostling about. In short: you should think like an engineer or architect yourself! A determined foot-long Engineer Goby can shift the base of live rocks substantially so make sure none of it is delicately balanced.
Use a glue to bond live rock pieces, coral frags, and other pieces of the aquascape to each other. That way, it’s very unlikely the Engineer Goby will engineer a collapse on you.
The substrate should also be something the Goby can dig through. Sand is ideal for juveniles. While it doesn’t always allow them to tunnel the young Gobies often simply burrow into it. As adults stick to large grained sand, gravel, or coral rubble as it holds its form better when the Goby builds its tunnels.
If your substrate isn’t very thick (less than 2 inches) make sure that your rock and coral are close (but not touching) the glass bottom of the tank. That way, any shifts as the Gobies undermine the structure are minor.
Lastly, live rock structures with gaps, holes, and cavities are greatly appreciated. This way you’re more likely to see your Engineer Goby above ground as it knows it has an infinite number of possible escapes if it feels threatened.
Are Engineer Gobies Reef-Safe?
Engineer Gobies are entirely reef-safe! They are harmless to corals, anemones, sponges, clams, and other sessile invertebrates. The only danger they pose is due to their digging.
Shifts in the live rock may result in a coral falling onto another coral. And since corals aggressively sting and poison each other, they may end up dead if you don’t notice in time.
Remember that Engineer Gobies are not always safe when it comes to small fish, shrimp, and other reef inhabitants, though…
Tank Mates for Engineer Gobies
Choosing tank mates for your Engineer Goby takes just a bit of thought but is mostly straightforward. Engineer Gobies are peaceful and social fish. But they are carnivores and opportunists.
Anything small and slow enough to be eaten is in danger from them. And they don’t exactly have tiny mouths, either. Small, thin fish, like Firefish (Nemateleotris sp.), smaller Gobies, and young Blennies are in danger of becoming a meal. As adults they tend to be thick enough to not be an easy meal.
Smaller saltwater shrimp are also in danger of being eaten. But adults of the larger species, such as Banded Coral Shrimp (Stenopus hispidus) are fine, as are other sizable crustaceans such as Arrow Crabs (Stenorhynchus sp.).
Starfish, Snails, Sea Urchins, Clams, and other unappetizing invertebrates are in no danger from an Engineer Goby. They may get pushed around a bit if they get too close to the burrow entrance, though!
Any fish too large to be easily eaten will make a fine tank mate as well. This includes Damselfish, Clownfish, Angelfish, Tangs, Dwarf Lionfish, and other typical marine community fish.
Even some aggressive fish like Triggerfish and larger Angels can work since the Engineer Goby will spend nearly all of its time around and in its burrow. But avoid keeping them with aggressive burrow-dwellers like Moray Eels.
Lastly, Engineer Gobies are quite social, both as juveniles and adults. The juveniles will stick together in schools when free swimming. As adults they form colonies of hundreds of individuals, both juvenile and adult, that share their tunnels and add to them over time.
Good Tank Mates for Engineer Gobies:
- Damselfish, Clownfish, Angelfish, Tangs, and other marine Community Fish
- Other Engineer Gobies
- Larger Crustaceans, Snails, Starfish, Sea Urchins, and other Invertebrates
- Corals, Sea Anemones, Sponges, and other Sessile Organisms
Poor Tank Mates for Engineer Gobies:
- Fish small enough to be eaten (Firefish, small Blennies, Gobies, etc)
- Tiny shrimp or crabs
- Aggressive tunnel dwellers (Moray Eels)
Feeding Engineer Gobies
The Engineer Goby is incredibly easy to feed. They are carnivores but don’t require live prey. In fact they are so slow and inept at catching food that it’s better not to give them live food.
Instead, give your Engineer Gobies a mixture of prepared and fresh or frozen carnivore delights. A sinking carnivore pellet ensures the Engineer Goby will get its share as flakes drift slowly and are likely to be snapped up by the other fish.
Supplement this with target feedings of thawed brine shrimp, bloodworms, mysis shrimp, krill, and other food. Once they are fully grown you may even feed them small pieces of chopped fish, shrimp, and squid from feeding tongs.
Engineer Gobies aren’t especially active (beyond digging) as adults. So a single heavy feeding a day is all they need!
Breeding Engineer Gobies
The Engineer Goby is one of the growing numbers of saltwater fish that are being bred in captivity. It takes a bit of luck and a spacious tank but just about anyone can breed these fish with a bit of patience!
One of the main reasons why breeding in home aquaria is still somewhat rare is that these fish are good sized, social, and the sexes look identical to one another. There aren’t any visual cues to tell males from females. Somehow the Engineer Gobies can tell but we can’t.
And since they live in large colonies as adults you need to provide them with a similar dynamic where the Gobies have a wide range of mates to choose from. This means providing enough space for 4-6 Engineer Gobies, at a minimum, to form a colony.
Lastly, the Engineer Goby doesn’t reach sexual maturity until 3-4 years of age. So patience is required as they put on size. But so long as you have several mature adults living harmoniously in a spacious tank, it’s very likely you’ll see babies!
Engineer Gobies spawn within their tunnels so you’ll probably never know when the event itself occurs. You can condition the fish with heavy feedings of high quality meaty food. But there are no known environmental triggers that induce spawning; simply sexual maturity, compatibility, and opportunity.
Once the eggs hatch, you’ll be treated to the sight of dozens to hundreds of free swimming young swirling near the entrance to the burrow. At the first sign of danger they will dash back to the safety of the lair. Unless they are threatened by the other fish in the tank you can let the parents raise them.
Baby Engineer Gobies will take live or frozen brine shrimp nauplii right away alongside copepods and other zooplankton. Simply feed them until they are large enough to accept small pellets and flakes. At this stage you can then work on finding them a new home at your local fish store!
