Please visit our Sponsors

Related FAQs: Convict Blennies

Related Articles: 

/The Conscientious Reef Aquarist

Convict Blennies, Family Pholidichthyidae

By Bob Fenner

A juvenile in Raja Ampat

This fish is an absolute delight. Pholidichthys leucotaenia, variously called the convict or engineer goby/blenny is neither a goby or a blenny, but still a very interesting aquarium specimen. 

    Most folks have only seen this fish when it's small, when it greatly resembles the common eel catfish, Plotosus lineatus in both appearance and behavior. Both are eel-shaped, social animals that "hang out" near rocky areas. The engineer goby is also overall blackish with a silvery white dorsal body line as juveniles… becoming more striped (convict suit-wise) with growth.  And yes this fish can grow. Almost always in good health, and amongst the last to perish from disease, poor environment or catastrophe, Pholidichthys is never "late to the dinner table"… and can grow to more than eighteen inches in length… in your reef to fish-only system. 

Convict blenny, family Pholidichthyidae; one species, Pholidichthys leucotaenia (Wirtz 1991), southwest Philippines to Solomon Islands. Juveniles and adults in captivity.

Bigger PIX:
The images in this table are linked to large (desktop size) copies. Click on "framed" images to go to the larger size.


            Is eminently easy with this species. Most all specimens are in superlative health. Pholidichthys ship and adapt well to captive conditions. Look for and buy them in a small group (they are social animals), of three or five individuals if your system has sufficient size. 


            A good-sized system (at least a hundred gallons for three specimens) with plenty of rock d?or that is, importantly, set right on the bottom in a secure manner. All heavy objects should be set in the tank first, and substrate placed after… to prevent toppling as this species is superb in its undermining activity (hence the name "engineer"). 


            Engineer gobies eagerly consume all types of foods. Getting them to feed on novel items is simply a matter of introducing them down near their favorite haunt/s. 


            This is a scaleless species that doesn't take well to exposure to harsh chemical treatments. Usually copper or formalin-containing medications are more toxic than a parasitic disease. Best to avoid having to use these altogether by quarantining new fishes for a good two weeks, assuring yourself that you've excluded the common external complaints of reef fishes. 


            Engineer gobies are unusual amongst coral fishes in their total lack of antagonism toward other fishes or invertebrates. They will eat very small fishes, crustaceans and worms, but otherwise leave larger-than-mouth size organisms totally alone. Reciprocally, all but the meanest of fishes leave them be, letting "live and let live" with the Pholidichthys residing in their dug out caverns and caves. 


            This fish has spawned in captivity and the young reared (see Wirtz 1991). Apparent pairs are formed that produce clutches of 400-500 young of about 6 mm. in length that lack a planktonic phase and are protected by their parents for about a month and a half. After this time they young are disbursed by the adults. 


            Though indeed an "oddball" as marine fishes go, the engineer goby, convict blenny, whatever you call Pholidichthys leucotaenia is a gem of a marine fish for aquarists. It's hardy to the extreme, accepting of almost all food and tankmate situations, intelligent and interesting behaviorally. It's only downside as a captive specimen is its prodigious digging behavior, and this is easily checked by careful arrangement of large rockwork being set solidly on their tank bottom to prevent toppling. 

Bibliography/Further Reading: 

Chlupaty, Peter. Undated. Pholidichthys leucotaenia- the white-striped eel goby. Aquarium Digest Intl. #34. 

Wirtz, Peter. 1991. Goby or blenny? Does the larva of Pholidichthys leucotaenia give a clue to the systematic position of the monotypic fish family Pholidichthyidae? TFH 10/91.

Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: