Not sure exactly where to put this thread so if it needs moving feel free
Ok I think I'm finished? Let me know if I'm not haha.
So a short introduction; while setting up our tanks I'm sure that at some point or another we have all considered a rare and exotic fish? Well I decided to do some research and compile a list of the oddball fish that are and are not suitable for the home aquarium.
What is an Oddball tank?
Oddballs are fish that do not necessarily fall directly into the more common categories of shoaling or community fish. Most have very unique characteristics and habits. Some will work in the average community tank with careful consideration, others may be very delicate or highly predatory and therefore only suitable for species tanks. Oddballs come in every shape and size.
The following fish may be suitable for community tanks, read carefully as they still do have very specific needs and may, for example, not be able to be housed with larger fish as they may be eaten, or visa versa!
15 US G plus
Threadfin Rainbowfish (Iriatherina werneri)
An interesting alternative to more well known shoaling fish. The Threadfin is very distinctive to look at and entirely peaceful. It's best to keep 1 male to 2-3 females, more than one male to a tank is advisable as this is when they show their best colours as they show off towards each other. They shouldn't fight. Due to their long fins it's best they're not kept with anything that may even slightly nip such as Tiger barbs.
Dwarf Pencilfish (Nannostomus marginatus)
The Dwarf Pencilfish is small and peaceful and an interesting alternative to Tetras. It's not strictly shoaling but does better with others of it's own kind, keep in groups of at least 3-4 or more and be prepared to separate them if any become overly dominant. They are tiny and shouldn't be kept with much larger or boisterous fish as they may be bullied or eaten.
Peacock Gudgeon (Tateurndina ocellicauda)
A small and not overly active Gudgeon, a trio would work well in this size tank (one male and two females). This fish is primarily mid-bottom dwelling and would do best with slow-swimming peaceful mid-top dwellers such as smaller Rasboras and Threadfin Rainbowfish. These fish may need to be target fed however as they are not quick to find food. The do not do well with a lot of current in the tank and prefer a soft sandy substrate and plenty of places to hide.
Bumblebee Goby (Brachygobius genus)
These are very tiny but curious little Gobys. There is some debate on whether they should really be kept in freshwater or only in brackish, indeed many have had success with both. The main thing to remember with these little guys is to not keep them with anything that can eat them! They are also known to fin nip, so are best kept with short-finned fish and will tolerate their own kind but can be territorial so space and hiding places should be provided.
Freshwater Neon Goby (Stiphodon atropurpureus)
A curious small Goby that can tolerate both freshwater and brackish also. It is an active algae grazer and therefore must be kept in a mature tank with algae growth, albeit they will only eat soft short algae, they will not eat filamentous algae. They should also accept blanched veges or sinking algae wafers. They are peaceful but territorial towards other Gobies. Male/female pairs should work. They appreciate a good current and rounded river rock décor as well as places to hide as they can be quite shy. Should not be kept with boisterous tank mates.
Fish for 113.6 Litres (30 US G.)
Dwarf Chameleon Fish (Badis badis)
These fish reach around 7.6cm (3") and while at first being shy, soon become far more outgoing and should therefore never be housed with shy fish, smaller fish nor anything long-finned. It should be perfectly fine housed with similar sized fish such as larger Danios. Décor should consist of tall planting and plenty of caves as well as subdued lighting. They do best in male/female pairs ideally, two males may well fight. This species is sometimes sold under the trade name of ‘chameleon fish’ due to its ability to rapidly change colour, especially when breeding or stressed
Madagascan Rainbowfish (Bedotia geayi)
These are peaceful shoaling fish that should be kept in groups of 5 or more (depending on overall tank size). Keep more females than males. They reach around 8.9cm (3.5") in length and should be kept with similar sized peaceful fish. It would be best to avoid anything with long fins or anything aggressive with these Rainbowfish.
Glass Catfish (Kryptopterus bicirrhis)
An interesting fish with an entirely transparent body. This catfish gets approximately 3-6" (7.6-15.2 cm) in length so requires a spacious tank. They can be pretty shy so must be in groups of at least 4-5 or more. They should cohabit peacefully with similar sized peaceful fish, but will be bullied by more boisterous fish. Does not cope in strong currents or very bright lighting, does best in densely planted mature tanks.
Indian Glassfish (Parambassis ranga)
Another fish species with a transparent body, although care must be made as these fish are often dyed fish victims. The Indian Glassfish is an active shoaling fish that should be kept in groups of 6 or more. They are generally peaceful and happy to be kept in community set ups with similar sized calm robust fish species, they do not do well in a frantic community set up. The males can be territorial and chase each other around, but this rarely results in any injury. They shouldn't be kept with long-finned fish as they may fin nip. A number of varieties of fish are sold that have been artificially colored. This is done in one of four main methods. The original method of artificially coloring fish is by injecting a paint under their skin. This was done with transparent fish, and gave rise to the painted glassfish. Recently, I've begun seeing glass catfish similarly "painted." If you ever are able to handle a dead one (and if you buy one, you likely will be able to), you can lightly squeeze the paint stripes and see them move: they remain fluid, under the fish's skin. This is bad for the the fish, it will live a short life and the dye will gradually fade. DO NOT BUY A FUDGING PAINTED FISH!!
Fish for 208.2 Litres (55 US G.) plus
Boesemani Rainbowfish (Melanotaenia boesemani)
A very colourful larger Rainbowfish that reaches around 12.7cm (5"). These are sociable fish and are best in groups, with more females per males, but keeping several males will result in the best colour displays. They shouldn't be kept with much smaller fish nor with very long-finned fish. They are active mid-swimming fish that do well in planted tanks with open swimming space.
Ropefish (Erpetoichthys calabaricus)
An unusual looking fish, indeed the only species in its genus and a cousin of the Bichir. The Ropefish is a nocturnal predator so must be kept with peaceful yet robust mid-top dwellers who are fast swimming and larger than the Ropefish. Smaller fish will be eaten. Their tank must be secure as these are well known escape artists! Provide them with a soft substrate and places to hide. They are not aggressive towards their own kind and do well in groups. In captivity they usually get to around 30.5cm (12"), maybe more, but in the wild they can reach in excess of 76.2cm (30")!!
African Knifefish (Xenomystus nigri)
One of the smaller Knifefish available, the African Knifefish is a nocturnal predator and its really best to keep one to a tank. They are a threat to small fish, but entirely peaceful towards larger fish. Keep with other peaceful larger fish such as Rainbowfish. They are sensitive to water quality so need mature tanks and plenty of hiding places.
Zig-Zag Eel (Mastacembelus circumcinctus)
A nocturnal Spiny Eel, the Zig-Zag is one of the smaller species. It is suitable with other fish as long as they're not small enough to eat, which rules out any fish 5.1cm (2") and under. Would be fine with larger robust fish such as Giant Danios or Boesemani Rainbowfish. It also does not mind its own species. They are burrowing fish so decor must be stable and substrate must be soft. They are also nocturnal so benefit from caves and tunnels in which to hide.
Fish for 283.9 Litres (75 US G.) plus
Black Ghost Knifefish (Apteronotus albifrons)
These are popular and the most commonly seen of the Knifefish and sold when quite small. Don't let that fool you. These guys should get at least 30.5cm (12"), in the wild they reach closer to 50.8cm (20")! They are nocturnal predators but have quite a small mouth and are peaceful towards larger tank mates, do not keep with fish 5.1cm (2") and under. They can also be quite shy so should not be kept with boisterous fish nor with suckermouth fish which may suck on the Knifefish's flanks. It is recommend that one BGK is kept to a tank, as they will bully and dominate one another. They should work fine in a spacious tank with plenty of hiding places with tank mates such as medium sized peaceful South American Cichlids such as Blue Acaras or larger peaceful Characins.
Fire Eel (Mastacembelus erythrotaenia)
A popular and stunning looking eel-like fish, this fish gets quite large, usually around 30.5-61cm (12-24") in captivity but can get over 76.2cm (30") in the wild! It is also a predator and should therefore only be housed with larger robust yet peaceful mid-top dwelling fish, smaller fish will be eaten. They often will not tolerate others of their own kind or similar species as they mature however. They should be provided with hiding places - PVC
pipe is popular with these fish.
False Siamese Tigerfish (Coius microlepis)
An attractive fish with bold vertical banding. It's only suitable for larger set ups and should either be kept singly or in groups of 5 or more. In smaller groups they are prone to aggression issues. Should not bother fish too large to be eaten, that being they should either match the False Tigerfish in size or be larger, yet robust and relatively peaceful.
Rainbow Snakehead (Channa bleheri)
One of the smaller of the Snakehead species. The Rainbow Snakehead works well in a community tank with larger robust species, it must be noted that smaller fish may well become food! It won't be very tolerating towards other Snakeheads either. You must make sure you have a secure tank if you consider one of these as they are excellent escape artists!
Oddballs for a Species Tank!
The following fish do not play well with others. Some may tolerate their own kind others are simply too aggressive or predatory to be kept with anything else.
Fish for 56.8 Litres (15 US G.) plus
Dwarf Puffer (Carinotetraodon travancoricus)
A tiny (1" long) puffer fish that thrives in 37.9 Litres (10 US G.) or larger. These curious little fish are also exceptionally aggressive. In a tank the décor should feature dense planting, caves and bogwood. These fish are very curious and need to be kept busy. In terms of stocking, two males should not be kept as they will fight to the death. It's generally recommended to keep 2-3 US G per fish, so therefore in a 56.8 Litres (15 US G.), you can keep 3 females and 1 male. Or 4 females.
Fish for 283.9 Litres (75 US G.) plus
Tiger Tetra (Hoplias malabaricus)
This is a large growing predatory fish in the Erythrinidae family. It has an impressive set of teeth and won't think anything of taking a lump out of tank mates! For this reason it's best to keep one of these fish to a tank, alone. It requires some secure décor as they will appreciate hiding places. Its not a very active fish, except at feeding time.
Oddballs to Avoid in the Home Aquarium!!
The following fish are best avoided unless you have very large aquaria, a bucket full of cash and a ton of patience! Many of these fish are also irritatingly common as juveniles in pet stores, buyer beware!!
Mbu Puffer (Tetraodon mbu)
A very very large Puffer often seen on sale when it's around the 15.2cm (6") mark. This fish should get around 61-73.7cm (24-29") long and be exceptionally messy with that. They are not suitable for any kind of community setting and will nip at and eat other fish. They do have excellent personalities and are rewarding if you are capable of housing something that needs a very long and wide tank just to itself!
Silver Arowana (Osteoglossum bicirrhosum)
The most common of all Arowana found on sale, and also the largest topping out at around 61-76.2cm (24-30"). They need very long and wide tanks as they have a large turning circle and suffer from disorders such as drop eye and gill curl if not cared for properly. These fish really need large tropical ponds and can be kept with similar sized peaceful yet robust mid-bottom dwelling fish, the Arowana is almost entirely top dwelling and perfectly capable of smashing through a flimsy tank lid! They will also eat smaller tank mates.
Clown Knifefish (Chitala chitala)
This fish is often seen in pet stores when anything from 7.6-10.2cm (3-4") to 30.5cm (12"), but, sadly, that's still only barely half-grown. These are very large Knifefish that need a large turning circle and therefore best only to be kept in large tropical ponds. They should eventually get around 88.9-121.9cm (35-48")!!
Feel free to add any fish you think I should add in here or to correct any information that I may have wrong