Rich Ross

Ribbon Eels are fascinating animals for public display but reports of the successful acclimation of these timid and finicky eels are rather uncommon.  There are many ideas about why these fish tend to fare poorly in captivity, including latent effects from cyanide poisoning, acute response to stress from shipping, and reluctance to feed on aquarium foods, but unfortunately they still remain one of the most difficult marine fish to maintain in captivity.  Despite their dismal track record there are rare instances of apparently healthy and thriving Ribbon Eels living in reef aquariums, but it is unclear what distinguishes these individuals to account for their acclimation to captivity. Continue reading for the full account of how these ribbon eels spawned in a captive aquarium.

Rich Ross

The Steinhart Aquarium at the California Academy of Sciences in San Francisco has publically displayed a pair of ribbon eels since 2008 under the care of biologist April Devitt, and this pair spawned during the early morning hours of July 16th, 2008 and June 12th, 2009.  The spawning was not directly observed, but the results of it were unmistakeable.  In both cases approximately 300 buoyant eggs 4mm across were released during the early morning and floated to the top of the exhibit (pictures after the jump).  As far as we can tell, instances of Ribbon Eels spawning in captivity are extremely rare; there is one report of a single spawn from a pair at a German public aquarium in 2001.  In the wild, ribbon eels go through dramatic color changes as they mature and change sex–juveniles are black, males are blue, and females are yellowish green.  One unexpected quirk of captivity is that despite being apparently sexually mature, these ribbon eels have remained “juvenile jet black” in color.  The 2001 account from Germany reported the same lack of color change–perhaps a critical nutrtitional or environmental component is missing to cue the color change, but in any case the internal sexual organs appear to work properly, at least in the female.

Unfortunately our experience with keeping the eggs alive long term has been disappointing; although we separated the eggs and kept them aerated in clean seawater, we did not see any larval development and they started to disintegrate after 3-4 days.  One thought was that the eggs were simply not viable because the male was not mature enough to fertilize them yet.  We hope to see the ribbon eels spawn again this summer in 2010, and hopefully we’ll see fertile eggs this time.

Rich Ross