41.24% of all known species of fish are found in fresh water

There are 92 species of freshwater fish occur in the country, where 50 of those are . 41% of all known species of fish of Sri Lanka are found in freshwater. There are about 70% of endemism of those fish. Most of them are listed into IUCN categories.

List of freshwater fish of Russia includes species of  found in , and includes those introduced.

The natural balance of both aquatic and terrestrial communities, including birds, mammals, reptiles, and other fishes, is dependent on fish populations that provide critical functions, such as cycling nutrients and serving as prey to a large variety of carnivores. The larvae of native freshwater mussels, called glochidia, require fish hosts in order to complete their life cycles. Some migratory fishes—such as shads, smelts, chars, and salmons—serve as keystone species of entire ecosystems. For instance, a variety of predators and scavengers feed on adults of migrating and spawning salmon, their eggs, fry, and their decaying carcasses. The nutrients that are transferred from the sea and incorporated into the food chain contribute to the health of forests adjacent to streams in which salmon spawn, thereby illustrating the linkage between terrestrial and aquatic habitats.7,16,17

Freshwater Fish Species - Take Me Fishing

A major purpose of Freshwater Fishes of Virginia is to provide a means to accurately identify all species of freshwater fishes of Virginia. I must note that your list of the top 10 exotic freshwater fish includes two that are not fish, one, an amphibian, two being a crustacean. As you did not seem to note this, perhaps we can go with your top 8 list:).
More seriously, however, is that while speaking of Silver Arowana, you depict an Asian arrowana, a fish very threatened, and current under the protection of CITES, among other laws, thus making them illegal to own without the correct permits. Please match your pic to the fish described, at least:).
I will also add that, saying Malawi cichlids, is simply is not specific enough to cover the many varieties of cichlids there; either be specific, or strike that from your list as well,as you might just have well said characin, expecting that to be specific enough to qualify for your list.
All in good fun, of course, but please do pull up your socks a bit.—rick

Fish Identification | Wildlife Resources Division

Virginia's fishes are rich in diversity and reflect the long history and varied habitat of the state. Cold- and warmwater streams, estuaries, farm and mill ponds, lakes, reservoirs, springs, and swamps support a variety of fishes from the smallest darter to the mammoth Atlantic sturgeon. Virginia's inland waters host more than 200 freshwater fish taxa and are carried by 10 major drainages to the Ohio and Mississippi rivers, as well as to the Atlantic Ocean. Freshwater Fishes of Virginia describes 210 species and 20 subspecies-native and introduced-divided among 24 families. The authors use early and current literature, museum records, recent surveys, and distributional data from more than 10,000 collections to compile the most comprehensive information ever assembled of Virginia's freshwater ichthyofauna.

SCDNR - Fish Species - Freshwater