Top 7 Oddball Fish for a 30-Gallon Aquarium

If you’ve already kept all of the most popular fish in the aquarium hobby, you may be looking for some oddball species to try. They tend to be unusual in appearance, have special care requirements, or may be harder to source. Because of their rarity, your friends and family are bound to ask what kind of strange creature they just spotted lurking in your aquarium. In previous articles, we covered our favorite choices for nano tanks, so let’s talk about the top 7 medium-sized oddballs for 29- or 30-gallon (100–114 L) tanks that are sure to pique your curiosity.

1. Glass Catfish

Kryptopterus vitreolus

The 2.5-inch (6.5 cm) Asian glass catfish or ghost catfish is immediately recognizable for its two long barbels and scaleless, transparent body. You can clearly see the skeleton and internal organs inside a silvery body cavity near the head. Found in the river basins of Thailand, they enjoy mildly acidic waters with soft to moderate hardness and tropical temperatures around 78°F (26°C). Unlike most catfish, they prefer to swim in the middle of the tank in tight schools, so get a group of six or more to help them feel more confident. Adding lots of aquarium plants for cover and shade to dim the lighting will also increase their comfort level. Keep your glass catfish with other peaceful, similar-sized fish that won’t bully them, and feed a variety of community fish foods, such as pellets, flakes, and daphnia.

2. African Butterflyfish

Pantodon buchholzi

The 4.8-inch (12 cm) freshwater butterflyfish is not related to saltwater butterflyfish but rather gets its common name from the giant pectoral fins that look similar to butterfly wings from the top view. The brown coloration makes it seem like a dead leaf floating at the surface as it waits for prey to swim by. Many people think of them as miniature arowanas because of their large, trapdoor mouth that is capable of gulping down smaller fish, so do not keep them with nano species. Plus, they can be semi-aggressive towards other top dwellers, including their own species, so consider just having one or getting a larger tank where you can keep a small group with lots of floating plants to block their line of sight. Finally, their long, trailing fins can be a tempting target, so avoid tank mates that like fin nipping.

Because butterflyfish mostly stay at the top of the water, the depth of the aquarium is not as important as the length and width. Most of the time, these ambush predators are quite sedentary, but you may see greater activity at dusk when the lighting is dimmer. They prefer slow flow at the surface and need a tight-fitting lid to prevent them from jumping out. Feed them meaty foods like freeze-dried krill, brine shrimp, bloodworms, and insects like crickets and mealworms. If they get hungry enough, you can successfully train them to eat dry, prepared foods such as floating pellets and Hikari Vibra Bites.

3. Wrestling Halfbeak

Dermogenys pusilla

Silver, platinum, and golden halfbeaks are just different color variants of the same species — the wrestling halfbeak. It has a long, slender body with a protruding lower jaw that looks like half of a bird’s beak. It can range from 2–3 inches (5–8 cm) long, with the female being larger than the male. This halfbeak is found all over Southeast Asia in fresh to slightly brackish water. Therefore, they like to live in alkaline pH with medium to high GH. As surface dwellers, they do best in slower currents with lots of floating plants as shelter to help increase fry survival rate and prevent squabbling among the males. You may see the males lock lips and wrestle with each other, so keep them in bigger groups with plenty of cover at the surface to minimize aggression.

Halfbeaks are livebearers that bear live young, but they are not as prolific as guppies or mollies. To condition them for breeding, keep their bellies full of floating pellets, fish flakes, and frozen foods. They will predate on smaller fish and their own offspring, so consider making a DIY fry trap to help protect the babies.

4. Empire Gudgeon

Hypseleotris compressa

This goby-like oddball has a tannish or olive-green body, a black spot right behind the gill plate, and fins that prominently display white, black, and red banding. Males are more colorful and bigger than females, reaching up to 4.5 inches (11 cm) in size. Plus, the males have a round nucal hump on the head with a red-orange face and belly, especially during mating seasons. This hardy species comes from Australia and New Guinea and can live in wide pH and temperature ranges, so you can even keep them in unheated fish tanks.

Empire gudgeons are fairly outgoing and active community fish that live in the bottom half of the aquarium. Males like to establish their own territories, so provide lots of hides and obstacles that block line of sight. They are not picky eaters and enjoy eating frozen foods, sinking pellets, and fish flakes. Unlike the more common peacock gudgeon, empire gudgeons are much harder to breed in captivity since their tiny young hatch out as underdeveloped larvae that require constant access to concentrated amounts of green water, smaller species of infusoria, and other nearly microscopic live foods.

5. Amazon Leaf Fish

Monocirrhus polyacanthus

The Amazon or South American leaffish is another ambush predator that pretends to look like a dead leaf. Its 3- to 4-inch (8–10 cm) oblong body is as flat as a pancake, the saw-toothed fins imitate serrated leaf edges, the dark horizontal stripe down the side seems like a leaf’s central vein, and even its lower jaw has a small filament that looks like a little stem. Instead of only floating up at the top, it patiently drifts throughout the water column by fluttering its transparent fins and may even pretend to lay on the ground like a sunken leaf. While it often has tan and brown marbling, the Amazon leaf fish can match its surroundings by changing colors to black, white, yellow, orange, and other shades. 

This South American species comes from slow-moving, acidic waters with pH below 6.5 and low GH. For camouflage purposes, their ideal environment should include broad-leafed plants like Amazon swords and large anubias, as well as lots of leaf litter on the substrate. While it can be kept in a group of its own kind and with other peaceful, medium-sized fish, this leaf fish is a voracious carnivore with a very large mouth that is capable of inhaling nano fish and shrimp. They enjoy eating live and frozen meaty foods, such as bloodworms, brine shrimp, little earthworms, and even small livebearers. In general, leaf fish can be hard to find and are usually recommended for more experienced fishkeepers.

6. Upside-Down Catfish

Synodontis nigriventris

Ever heard of a fish that likes to swim upside-down? This 3- to 4-inch (8–10 cm) catfish starts off swimming right-side up as a juvenile but quickly develops the habit of swimming on its back after two months of age. They use this amazing ability to feed on the undersides of hardscape and leaves, so fill their tank with caves, aquarium plants, and other shelters for them to rest and graze beneath. Most fish have light-colored bellies that look like the sky when viewed from below, but because of its inverted lifestyle, this species has an abdomen that is darker than the rest of its brown, splotchy body so that it blends in with the ground when viewed from above.

Upside-down catfish originate from the Congo River basin of Africa and like to hang out near the riverbanks where lots of plants grow. They can tolerate a wide range of pH and GH with typical tropical temperatures around 78°F (26°C). They do have a nocturnal lifestyle, so dim the lighting and feed them at night to see their interesting swimming style. As an omnivorous scavenger, they use their mouths to scrape on surfaces and will eat almost anything, such as Repashy gel food and sinking wafers. This peaceful catfish feels most comfortable in a school of its own kind and can be kept with similar-sized community fish, but they will opportunistically feed on smaller fish and dwarf shrimp if given the chance.

7. Blue Crayfish

Procambarus alleni

The Florida crayfish, also called the electric blue crayfish or blue lobster, is a freshwater crustacean that is native to Florida in the United States. They are normally brownish, but blue is a color mutation that naturally occurs and is now popularized in the aquarium hobby. Keep this escape artist in an unheated aquarium below 70°F (21°C) with a very tight-fitting lid. As vegetable eaters, they may dig up and snack on your plants, so consider using floating plants or very strong, emersed-grown plants like mangroves and lucky bamboo (Dracaena sanderiana). They need harder water to aid with proper molting, so if your water has low GH, make sure to dose mineral supplements (e.g., Wonder Shell and Seachem Equilibrium). Also, feed calcium-enriched foods for invertebrates, such as Hikari Crab Cuisine and Xtreme Shrimpee Sinking Sticks. After molting their old exoskeleton, crayfish will disappear into caves and other hiding spots while their new exoskeleton is still hardening.

Tank mates can be a bit tricky since this 4- to 6-inch (10–15 cm) crayfish will eat smaller animals, but they are also in danger of being eaten themselves by bigger animals, especially right after molting. Plus, they can get aggressive with their own species, so if you want to keep multiple crayfish, get a bigger tank with more hides scattered around. Because they are slow-moving critters, consider keeping them with fast-swimming, peaceful fish like white cloud mountain minnows or zebra danios that stay mostly in the upper half of the tank and won’t pick on them. Just don’t be surprised if some of the fish disappear, so livebearers that overbreed may also be another option.

After learning about all these interesting creatures, we hope you are inspired to set up your own oddball aquarium. While we do not ship live fish, you can check out the stocking lists of our preferred online retailers. For more ideas, read about our top 5 oddball species to keep in a 20-gallon fish tank.