There is a section on these fish in my upcoming book, "Advanced Marine Aquarium Techniques" due out from TFH this month.
Jay Hemdal
P. S. - Do you have one now? If so, the book may not be out in time to help - so here is an excerpt from that section: (Copyright 2006 TFH Publications)
Misinformation about this species abounds in the hobbyist literature. Virtually every mention of them in books makes a comment about their hardy nature, cavernous mouth and preference for feeding on large invertebrates such as adult brine shrimp. In most cases, their secretive habits are also described at length. What then should a hobbyist think when they acquire one and it contradicts this information by refusing all food, spending all of its time swimming out in the open and then dying in a few weeks?
Success with this species starts with acquiring one that is very healthy, and therefore more likely to adapt to the confines of an aquarium. Never purchase a black widow that has torn fins, or one that is too emaciated. Due to their stringent feeding requirements, virtually all of these fish will be a bit thin from not having been fed properly since capture. They may be able to recover from a short fast, but they almost never survive if they have become severe emaciated. This is characterized by not only a sunken belly, but by loss of muscle tissue at the nape of the fish, behind the head. Once you have purchased a specimen that passes these visual criteria, acclimate it to a small aquarium by itself so that you can monitor its feeding activities, and keep it from being attacked by tankmates. The water quality should be optimal, the temperature can range from 74 to 80 degrees and surprisingly, lighting is not really an issue. You would think that an obligate cave dweller like the black widow would abhor bright light, but this is not the case with this species in captivity. A few pieces of PVC pipe cut into short lengths can serve as ââ"šÂ¬Ã…"œcavesââ"šÂ¬Ã‚ for the fish, but you will likely not see them used too often. One author stated that this species is a ââ"šÂ¬Ã…"œjumperââ"šÂ¬Ã‚Â. This has not been reported by other people, but it is always prudent to keep any fish in a covered aquarium.
The critical issue with black widows in captivity is diet. As stated, the vast majority of these fish starve to death in captivity. Their large mouth seems to indicate that they feed on large invertebrates, but this is not the case. One author steadfastly maintained that this is true, despite never having seen a black widow feed, ââ"šÂ¬Ã…"œÃƒÂ¢Ã¢"šÂ¬Ã‚¦food seems to be taken during the night.ââ"šÂ¬Ã‚ This is just dreaming, a healthy black widow will feed during the day, just not on large food items! The key to getting a black widow to eat is to offer it live brine shrimp nauplii, or better yet, larval mysid shrimp. Do not expect to see the black widow chase and consume food in mid-water like most other fish do. This species has a possibly unique feeding strategy; it slides on its side along smooth surfaces and into crevices and snaps up any food items clinging there. It is likely that they do not use their sight at all in the feeding process. The black widowââ"šÂ¬Ã¢"žÂ¢s high profile head means that they cannot see well directly in front of them, so they most likely just blindly snap their jaws whenever they ââ"šÂ¬Ã…"œbumpââ"šÂ¬Ã‚ into some food. One black widowââ"šÂ¬Ã¢"žÂ¢s favorite feeding technique was to swim along the crevice made by the junction of a piece of PVC pipe and the floor of the aquarium. Other times, these fish will slide along the sides of the aquarium. It is possible that the ââ"šÂ¬Ã…"œcleaning behaviorââ"šÂ¬Ã‚ noticed by others was simply the black widow using the side of a larger fish in the same manner. When the black widow is successful in capturing some food, it will keep moving forward. If it misses, youââ"šÂ¬Ã¢"žÂ¢ll often see the fish shake its head and snap again, or back up a bit and snap, apparently trying for the food a second time. Evidently, the black widowââ"šÂ¬Ã¢"žÂ¢s normal feeding technique can only be partially met in captivity. Even the individuals that do begin feeding most never seem to feed with much gusto, and do not grow well.