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 unique physiology. Here are five of the most unusual fish you can keep in your 20-gallon aquarium.


1. Marbled Hachetfish

Carnegiella strigata

This hatchetfish is a tiny species measuring 1.25 inches (3 cm). It has a prominent chest, resembling a hatchet knife. The body of this pearly-white hatchetfish is covered with beautiful, dark marbling. The pectoral fins extend out like tiny wings. They come from tannin-filled black waters in the Amazon basin of South America, which tends to have acidic pH and tropical temperatures, but they are accustomed to handling a wide range of water parameters because the area is subject to annual flooding.

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. To help them feel more comfortable, add floating plants like water sprite as shelter and get a school of at least six marbled hatchetfish because the more the merrier. This species can be paired with peaceful community fish that live in the aquarium’s middle and bottom layers. Small mouths make it difficult to feed these fish small floating foods like Easy Fry and Small Fish Feed, crushed flakes and baby brine shrimps and daphnia. Our hatchetfish care guide has more details.

2. Stiphodon Goby

Stiphodon ornatus

Stiphodon genus is a group of freshwater gobies that hail from Asia and Oceania. They have a slim, eel-like body, similar to kuhli loaches, but about half their length at 2 inches (5 cm). Similar to otocinclus catfish they are aufwuchs grazers. They eat any algae, zooplankton or biofilm that grows on surfaces. Repashy Soilent Green and frozen daphnia are their favourite foods. Stiphodon gobies make great community fish. However, males can be a little feisty towards each other so give them plenty of hiding places and think about getting more girls than the boys.

3. Peacock Gudgeon

Tateurndina ocellicauda

The amazing rainbow colors of the peacock-gudgeon are what gave it its name. Imagine a 2.5-inch (6 cm), pink body with red vertical stripes, blue speckling, yellow-rimmed fins, and a black spot at the base of the tail. As you can see in the above picture, males have a distinctive nuchal hump in their forehands. Females have a more straight forehead similar to a tetra or danoio. They originate from Papua New Guinea. They prefer the lower half of an aquarium. That being said, they are not picky eaters and are happy to consume any floating and sinking community fish foods you feed them. They are generally mild-mannered, but males can be territorial during breeding season. It is easy to spawn them if both sexes are present and you provide 1-inch (22.5 cm) PVC pipes so they can lay their eggs.

4. Blind Cave Tetra

Astyanax mexicanus

In nature, this species actually comes in two forms – (1) a normal version found in rivers and lakes that looks like an ordinary, silvery tetra and (2) a blind cave version found in underground waterways and caverns in Mexico. The latter type is more popular in the aquarium hobby because of its shiny, pinkish body and undeveloped eyes covered by skin. Despite being blind, they are able to find food easily with their enhanced senses. This schooling fish is able to grow to about 3-3.5 inches (8-9cm), and can survive in a cool aquarium without heating. Although they are considered a good community fish, they can be aggressive and will nip at anything to explore their surroundings. Keep them away from slower-moving fish or those with long fins. Keep them happy with a variety community food like pellets, gel foods, and flakes.

5. Top Hat Blenny

Omobranchus fasciolatoceps

Blennies predominently come from saltwater habitats, which is a shame for freshwater hobbyists because they have such fun personalities and interesting behaviors. Luckily, there are some species that live in brackish water, like the top hat blenny that comes from southern Japan and China. They are often marketed as a freshwater blenny, but in our experience, they do best in brackish water with alkaline pH, higher GH, and tropical temperatures. As per their common name, males have a rounded crest atop their head, and their entire head and face has a striking pattern of vertical, yellow striping. The rest of their 2.5 to 3 inch (6-8 cm) long, elongated bodies is brown or grayish in color and ends with a yellow tail. They are usually peaceful fish. But males may fight over territory so they need rockwork and caves to shelter them. They love brine shrimps, baby brine shrimps, dried seaweed, spirulina flakes, and algae that you scrape from the tank sides.

If you are looking for oddball fish and don’t have enough space to put up a 10-gallon tank, our previous article will help you find some of our top picks.