Top 5 Oddball Fish for A 20-Gallon Aquarium

Top 5 Oddball Fish for a 20-Gallon Aquarium

Looking for a fish that is bizarre in appearance, has unique behaviors, or is rarer in availability? There is a whole category of fish for aquarium hobbyists that are “oddball” species. Some species are very hardy and easy to maintain, while others require special care due to their unusual physiology. Discover five of the most bizarre fish that you can keep inside a 20-gallon aquarium.


1. Marbled Hachetfish

Carnegiella strigata

This species measures in at 1.25 inches (3cm) and features a prominent chest that resembles a hatchet blade. The pearly, light-colored body has beautiful, dark marbling. Its pectoral fins are shaped like wings. They were born in tannin-rich black waters of the Amazon basin, South America. These waters tend to be acidic and tropical, but they are used to handling all water parameters.

Hatchetfish are top-dwelling fish and can jump out of the water to escape predators. Make sure your aquarium has a tight-fitting lid. Cover any openings with craft mesh, or other materials. They will feel more comfortable if you add floating plants such water sprite and create a school of at minimum six marbled hatchetfish. This species pairs well with other peaceful community fish that swim in the middle and bottom layers of the aquarium. You can feed them tiny floating foods such as crushed flakes, easy fry and small fish food, baby brine shrimp and daphnia because of their small mouths. See our hatchetfish care manual for more information.

2. Stiphodon Goby

Stiphodon ornatus

Stiphodon genus includes freshwater gobies from Asia, Oceania. They are eel-like in shape and have about two inches (5 cm) of length. They are aufwuchs grazers just like otocinclus Catfish. This means they eat algae and zooplankton as well as biofilm growing on surfaces. Repashy Soilent Green and frozen daphnia are their favourite foods. While Stiphodon gobies are excellent community fish, the males can sometimes be a bit feisty towards one other, so provide plenty of hiding spots and consider getting more girls than boys, even though the females are less colorful.

3. Peacock Gudgeon

Tateurndina ocellicauda

The incredible array of rainbow colors that make up the peacock’s gudgeon name is what gives it its common name. Imagine a pink 2.5-inch (6 cm) body with blue vertical stripes, blue spekling and yellow-rimmed tail. As seen in the image above, the males have a distinct nuchal-hump on their forehands. The females, however, have a more sleek forehead that is similar to a tetra/danio. They are from Papua New Guinea. Their preferred habitat is the aquarium’s bottom. They aren’t picky eaters, and will eat any floating or sinking fish food you give them. Although they are usually mild-mannered, males can become territorial when breeding seasons come around. It is easy to spawn them if both sexes are present and you provide 1-inch (2.5cm) PVC pipes to allow them to lay their eggs.

4. Blind Cave Tetra

Astyanax mexicanus

This species is actually found in two varieties in nature. There’s a (1) normal version that can be found in rivers or lakes, which looks like an ordinary, silvery Tetra, and (2) blind cave versions found underground and in caverns in Mexico. This latter variety is more common in the aquarium hobby due to its shiny, pinkish body with undeveloped eyes that are covered by skin. Despite their blindness, they can find food using their enhanced senses. This schooling fish is able to grow to about 3-3.5 inches (8-9cm), and can live in a cool, water-cooled aquarium that does not have a heater. This fish is considered a “community fish” but they do like to explore the surroundings. They will not tolerate slow-moving or long-finned species. Offer a variety of community foods like flakes, pellets, gel food, and frozen foods to keep them happy and well-fed.

5. Top Hat Blenny

Omobranchus fasciolatoceps

Blennies are mainly found in saltwater habitats. This is a shame for freshwater hobbyists as they have so many interesting personalities and behaviors. There are some species that can live in brackish waters, such as the top-hat blenny from China and southern Japan. While they are often called a freshwater blenny by some, their preference is for brackish water that has a higher pH, higher GH and tropical temperatures. According to their common name, males have an oval crest at the top of their heads, and their entire face and head are covered with yellow stripes. The rest of their 2.5- to 3-inch (6-8 cm) elongated body is a brown or grayish color that ends in a yellow tail. They are usually peaceful fish. But males will fight for territory. So provide rockwork and caves so they can find shelter. You can find them eating brine shrimp, baby salt shrimp, dried seaweed and spirulina flakes.

If you don’t have the space for a 10-gallon fish tank but love the idea of oddballs, we recommend our previous article. It covers our favorite nano-sized picks.