Fish are one of the most diverse animals, inhabiting water with different parameters, including salinity.

       Some fish occur both in freshwater and saltwater environments, and we can use this feature in our aquariums, whether to populate a new tank or convert a freshwater aquarium to saltwater.

       The following are some species commonly kept in freshwater that can also be kept in saltwater.

Molly Fish

       Hardly an aquarist will not recognize a Molly fish. Poecilia latipinna, P. sphenops, or P. velifera are some of the most striking mollies and inhabit coastal areas ranging from the southern United States to northern South America, predominantly in Mexico.

       In common, these species have an insatiable taste for insect larvae, plants, and even worms. They prefer densely vegetated environments with a tropical temperature (25º-28ºC). They can reach 5.9 inches, depending on the species.

Flagfish (Jordanella floridae)

       It is not an uncommon species, as many know this fish; perhaps what most do not know is that it is a fish that lives in brackish environments in Florida, United States (St. Johns and Ochlocknee rivers) and is considered a killifish.

       Despite its size, around 2 inches, this fish has similar eating habits to mollies, aquarium layout, and even water parameters.

Bumblebee Fish (Brachygobius xanthozonus)

       Coming from Java, Sumatra, and Borneo, this tiny (up to 2 in) and graceful fish fits in small volumes. However, the male’s territoriality must be considered, which emerges in an intraspecific aggressiveness. Groups with a minimum of 6 individuals should be placed in aquariums with vegetation and hiding areas.

       As a “Gobie,” it lives in contact with the bottom of the aquarium. Carnivorous need live food, although they learn to eat frozen food. It doesn’t change much in water parameters; the temperature is 22-28°C.

Indian Glass Fish (Parambassis ranga)

       This fish, originally from Asia (Thailand, India, Pakistan, Bangladesh, Nepal, Malaysia, and Myanmar), is considered peaceful and shy. It grows up to 3 in, and its palate accepts anything, having no restrictions on industrialized food.

       Large aquariums are not required for the species. The water must be at a temperature between 20 and 30ºC, perhaps one of the least demanding among the fish on this list.

Orange Chromide (Etroplus maculatus)

       A species known in the aquarium hobby for a long time originates from lakes and streams in India and Sri Lanka, which have contact with estuaries.

       It grows up to 4 inches and likes to swim among the vegetation and submerged roots. It preys on baby fish, zooplankton, and also algae. It is usually peaceful, even though it is a cichlid. It is equal to the others in terms of temperature. However, it adapts better to a slightly higher pH.

Spotted Scat (Scatophagus argus)

       It is a widely distributed Asian fish that transits between the fresh and marine waters of the Indo-Pacific, Kuwait, Fiji, and even Japan.

       They are large, over 11 in, so tanks of at least 80 gallons are required. They are omnivorous but require a plant-based diet, in addition to being able to prey on smaller fish. As for water parameters, it is of good size at a temperature of 22-28ºC.

Silver Moony (Monodactylus argenteus)

       With the same particularities as the Scat, this silverfish is around 9.8 inches. Its origin overlaps with the friend above, expanding to the Persian Gulf, East Africa, and Australia.

Mudskipper (Periophthalmus barbarus)

       There are dozens of Gobie species in this genus, and this is one of the most common and widely distributed (West Africa, India, Thailand, Bangladesh, Philippines, and Australia). They reach 6 in and are not very friendly, yet they are sought after in the hobby.

       Although he makes his burrows in the mud, I wouldn’t be able to recommend this to aquarists; many hobbyists use the same substrate used in marine aquariums in layouts that contain rocks and burrows without causing problems to the fish.

       As it is known to leave the water to walk (they protect water in the gill chambers, which prevent drying), it is recommended to leave exposed areas so that he can come to the surface – this is the moment that aquarists use to feed them. And by the way, food is crucial: live food! It eats everything: insects, crustaceans, and small fish; they accept frozen brine shrimp and bloodworms. However, they will hardly eat industrialized feed. The water temperature is around 25-30ºC.

Banded Archer Fish (Toxotes jaculatrix)

       This fish, coming from the Indo-Pacific (from the Indian coast to northern Australia), is known to “spit” out of the water, hitting insects, souping up leaves near the water, and then eating them. And this is the detail that weighs, as it requires live insects in the diet; alternatives are seen in frozen food (brine shrimp and bloodworms) and, rarely, in pellet food.

       They are big, about 9 in, inhabiting the water column from the middle to the surface of the aquarium. Some recreate the environment, having in the aerial part plants that hang close to the water and place the insects in them to encourage their fish to target them with a jet of water. Keep temperature 25-28ºC.

Four-Eyed Fish (Anableps anableps)

      It occurs from Venezuela to the delta of the Amazon River in Brazil. They are gregarious and like to be among some floating vegetation, roots, and driftwood that protrudes through the water.

       They reach 1 ft, which, added to the fact that they like to live on shoals, need large aquariums greater than 95 gallons. Although their positioning is on the surface, the “Four Eyes” (2 eyes in the water and two out – it has two corneas, two pupils, and one retina) eat everything from algae on roots, fish, and insects, even carcasses. They prefer temperatures around 25-30ºC.