I am aware of the brotula being cryptid. They are one of the most unique and interesting reef fish from that area IMO, so it's a must have for me.
How about the brotula, banner goby, basslet (or some other demersal fish cause I don't wanna spend $200 rn), and the arrow crab?
I wrote an article on black widow brotulids many years ago. I found the text on my computer:
The Black Widow Brotula
, Stygnobrotula latebricola
Probably the most enigmatic fish available to home aquarists, the black widow is rarely seen and few people have any success keeping it alive for very long. Jet-black to dark brown in color, (depending on how the light strikes them) their single long fin ripples with an almost hypnotic motion. Their monochromatic color scheme makes it difficult to see, but if you look closely, they have a decidedly sullen expression about them. While the bottlenose dolphin always appears so happy due to its large upturned mouth, permanently fixed in a “smile”, the poor black widow goes through life with a perpetual frown. Some people think this fish’s face is reminiscent of a sperm whale’s, with the large mouth, black color and blunt steep forehead.
Related to the cusk eels, black widows belong to the family Bythitidae, the viviparous brotulas. This means they give birth to live young, a rare thing among coral reef fishes. This activity has not yet been reported from captive individuals, although a photo of a gravid female living in the wild has been shown. The black widow reportedly grows to a length of 3 inches, but most seen in pet stores are around 2 inches long. It has been reported anecdotally that they are at least part-time cleaner fish, picking parasites from the bodies of larger fish. This behavior has not been seen in captive fish, when housed with other species, the black widow most often simply ends up with its fins shredded. The “gold widow”
Ogilbia cayorum is a related fish sometimes seen offered for sale. It grows a bit larger (to 5”), and is more full-bodied than the black widow. It is a hardier species, but still not a good candidate for a typical community aquarium.
Scientists have reported it to be a common fish in shallow water caves throughout the Caribbean and Florida reef tracts. Fish collectors maintain that this is an exceedingly rare species and rarely offer them for sale. Why the discrepancy between these two groups? The scientists sample reef life using rotenone or other powerful chemicals to drive fish out of the coral caves and crevices. Fish collectors need their prey alive, so do not, (at least in the United States) use such strong chemicals to make their captures. In most cases, the tropical fish collector is working with quinaldine to capture some fish they have just spotted, perhaps a pygmy angelfish. The angel tucks itself into a crevice and the collector gives the hole a spray of “juice”. Out comes the sedated angelfish, but also sometimes fish living unseen in the crevice are affected as well. Usually these are just cardinalfish or some plain colored goby, but once in a great while out comes the odd looking black widow. Well-informed fish collectors know this is an unusual fish and will usually take the time to bring it back with them. However, incomplete knowledge of this fish’s husbandry requirements often means that they hold the fish under poor conditions prior to sale. Black widows seem very prone to aggression by tankmates; almost every individual seen offered for sale will have ripped and torn fins from being picked on by other fish. In addition, black widows have specialized feeding habits, so invariably the ones that have been held in captivity for any length of time are very thin.
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 “caves” for the fish, but you will likely not see them used too often. One author stated that this species is a “jumper”. 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, “…food seems to be taken during the night.” 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 widow’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 “bump” into some food. One black widow’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 “cleaning behavior” 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, you’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 widow’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. This is similar to what is seen with some other “problem feeding” fish such as pinnatus batfish and orange-spot filefish. In addition, even if the fish does begin feeding well on brine shrimp nauplii, this is not a nutritionally complete diet, and is lacking in some essential fatty acids. This means that for long-term success, the aquarist must either fortify the brine shrimp with Selco™, (or other enrichment product) or better yet, feed a second food item, such as larval mysid shrimp.
The black widow obviously is not for every aquarist. While not impossible to keep alive, they certainly are not as hardy as people have been lead to believe. Hopefully, now aquarists who buy one will have a fighting chance to keep it alive, and other aquarists, knowing the extra effort it takes, will not casually acquire one.
