I initially scheduled this as clade Ovalentaria rather than making separate polls for the 6 orders within it, because there were some families and genera that hadn’t yet been filed into orders, and I didn’t want them getting left out. Since I made the schedule, this has now been resolved. Yay. Turns out 2025 has been a big year for fish taxonomy. 🙃 Oh well, this is just an extra large poll that probably includes some of your favorites!

Ovalentaria contains many of the most colorful marine and freshwater fish in the world, and many of the most popular home aquarium fish

The entire Bedotiidae family, the Madagascar rainbowfishes, are endemic to Madagascar. They occur exclusively in freshwater environments and are distributed in small to medium-sized forested rivers and streams, or occasionally in swamps and marshes, in Madagascar. Many of these species, such as the endangered Zona (Bedotia geayi) and Katrana (Rheocles alaotrensis), are under severe threat because of rapid deforestation and habitat modification throughout most of their range.

Needlefish (family Belonidae) (image 3) are elongated with long, narrow jaws filled with sharp teeth, causing some species of needlefishes are referred to as “gars” or “garfish”, though they are very distantly related to actual gars. Needlefish have been documented in taking advantage of “Snell's Window” when attacking prey; leaping at a shallow angle to ambush schools of small fish. Due to light refraction through water, objects at the edges of Snell’s Window appear distorted, disrupting the image of the leaping needlefish and allowing it to get within very short distances of its prey.

Since needlefish swim near the surface, they often leap over the decks of shallow boats rather than going around. This jumping activity is greatly excited by artificial light at night, and night fisherman and divers in areas across the Pacific Ocean have been "attacked" by schools of suddenly excited needlefish diving across the water towards the light source at high speed. Their sharp beaks are capable of inflicting deep puncture wounds, sometimes breaking off inside the victim in the process. For many traditional Pacific Islander communities, who primarily fish on reefs from low boats, needlefish represent an even greater risk of injury than sharks. Needlefish are responsible for at least 7 documented deaths and 4 serious injuries.

Halfbeaks (family Hemiramphidae), who have an extended lower jaw but not an upper one, are omnivores feeding on algae, marine plants, plankton, invertebrates, and smaller fishes. For some subtropical species at least, juveniles are more predatory than adults. Some tropical species feed on animals during the day and plants at night, while other species alternate between carnivory in the summer and herbivory in the winter.

While they do not "fly" in the same way a bird does, Flying Fish (family Exocoetidae) (image 2) can make powerful leaps out of the water where their long wing-like fins enable gliding for considerable distances above the water's surface. The flights of flying fish are typically around 50 m (160 ft), though they can use updrafts at the leading edge of waves to cover distances up to 400 m (1,300 ft). They can travel at speeds of more than 70 km/h (43 mph). The main reason for this behavior is thought to be to escape from underwater predators, like swordfish, mackerel, tuna, and marlin, though their periods of flight unfortunately expose them to attack by avian predators such as frigate birds. Barbados is known as "the land of the flying fish" and the fish is one of the national symbols of the country.

The Japanese Rice Fish (Oryzias latipes), also known as the Medaka, is a popular model organism used in research in developmental biology. This species has been sent into space, where they have the distinction of being the first vertebrate to mate and produce healthy young in space.

As an adaptation to living in ephemeral waters, the eggs of most killifish (image 4) can survive periods of partial dehydration, some even depending on drying out in order to hatch, and the eggs would not survive more than a few weeks if entirely submerged in water.

The Mangrove Rivulus (Kryptolebias marmoratus), a species of killifish, mostly breeds by self-fertilization and adults can survive for about two months on land. Males are rare, and can only hatch from eggs kept below 19 °C (66 °F).

The Turquoise Killifish (Nothobranchius furzeri) is the shortest-living vertebrate that can be bred in captivity, having a natural lifespan of between three and nine months.

The Flagfish (Jordanella floridae) is a killifish endemic only to Florida, USA, and it is named after the pattern on dominant males resembling the flag of the United States. They are sometimes kept in fish tanks to naturally control hair algae in suitable aquariums, as they are one of the only fish to consume it in an impactful volume.

The most famous pupfish is probably the Devils Hole Pupfish (Cyprinodon diabolis). It is a critically endangered species found only in Devil’s Hole, a water-filled cavern in the US state of Nevada. When nearby agricultural irrigation caused the water to drop in the cavern, several court cases ensued, resulting in Devils Hole being declared a National Monument in 1952, including the preservation of adequate groundwater to maintain the pool. As of September 2022, the count showed a total of 263 observed wild pupfish, up from only 35 in 2013.

Four-eyed Fishes (genus Anableps) are so named because their eyes are divided in two different parts, so that they can see below and above the water surface at the same time. They and their relatives, the Onesided Livebearers (genus Jenynsia) mate only on one side, right-"handed" males with left-"handed" females and vice versa.

The Western Mosquitofish (Gambusia affinis) is a small livebearer which eats zooplankton, beetles, mayflies, caddisflies, mites, and other invertebrates, with mosquito larvae actually making up only a small portion of their diet. However, due to their ease of keeping and high adaptability, they have been used more than any other fishes for the biological control of mosquitoes, and are often kept in manmade ponds and other bodies of water to keep mosquito populations down. Unfortunately, this has also caused them to be incidentally introduced to natural areas, where they reek havoc on native invertebrate populations, and have even exacerbated the mosquito problem in many areas by outcompeting native invertebrate predators of mosquito larvae.

Leaffishes (family Polycentridae) are highly specialized ambush predators that resemble leaves, down to the point that their swimming style resembles a drifting leaf. When a prey animal, such as an aquatic insect or smaller fish, comes within range, the fish attacks, swallowing the prey within a quarter of a second.

The Convict Blenny, also called the Convict Goby, Engineer Blenny, or Engineer Goby (Pholidichthys leucotaenia) is neither blenny nor goby, but one of the two species in the family Pholidichthyidae, most closely related to cichlids and leaffishes. They have small, eel-like bodies, and juveniles mimic the venomous Striped Eel Catfish (Plotosus lineatus). As they grow, the stripe changes to white convict-style barring or spotting in the adult. Adult schools of Convict Blenny swim in such tight formations that they resemble a single organism.

Cichlids (family Cichlidae) (image 1) are some of the most colorful freshwater fish, even forming “reefs” in the rocky freshwater lakes of Africa.

Because of the introduced Nile Perch (Lates niloticus), Nile Tilapia (Oreochromis niloticus), and water hyacinth, deforestation that led to water siltation, and overfishing, many Lake Victoria cichlid species have become extinct or been drastically reduced. By around 1980, lake fisheries yielded only 1% cichlids, a drastic decline from 80% in earlier years.

Cichlids provide scientists with a unique perspective of speciation, having become extremely diverse in the recent geological past, those of Lake Victoria actually within the last 10,000 to 15,000 years, a small fraction of the millions taken for Galápagos finch speciation in Darwin's textbook case.

The Bumblebee Cichlid (Pseudotropheus crabro) specializes in feeding on parasites from the Kampango (Bagrus meridionalis). The Kampango recognizes the cichlid as a cleaner, and will allow it to approach to clean off parasites. However, the Bumblebee Cichlid has also been found preying upon the eggs of the Kampango, but will change colour to a dark brown while doing so, seemingly as to not tarnish its cleaning relationship with the catfish.

All cichlids practice some form of parental care for their eggs and fry, usually in the form of guarding the eggs and fry or mouthbrooding.

The Indian Glassy Fish (Parambassis ranga) is transparent, and showier specimens that had been injected with artificial coloring were sold as novelty pets in the 1990s. Since then, these "painted fish" have become much less popular, replaced by fish that have been genetically modified to display neon colors, rather than be injected with them.

Mullets (Mugilidae) have served as an important source of food in Mediterranean Europe since Roman times. In ancient Egypt they ate pickled and dried mullet called fesikh.

While most damselfish live on reefs in shallow water, the Chromis abyssus has been found below 100 m (330 ft) deep.

The Dusky Farmerfish (Stegastes nigricans) is a damselfish so named because it is known for farming monocultures of algae such as cyanophores and rhodophytes. The fish will claim a patch of its preferred algae, which it defends by chasing away other fish and sea urchins. The fish also weeds out other bits of algae that attempt to grow in the patch and swims outside of its territory to spit the invading algae out. There are nine algae species that the Dusky Farmerfish will farm for, and the algae they remove is competitive and faster growing than their preferred delicate algae. These species of algae are dependent on the Dusky Farmerfish for survival, and the presence of the species greatly increases the primary productivity of the area by boosting oxygen, nitrogen, and phosphorus concentrations.

Clownfishes, or Anemonefishes (genus Amphiprion) (see gif above) are some of the most well-known damselfish, made famous by Pixar’s Finding Nemo. They are known for their mutualistic and symbiotic relationship with sea anemones. They acclimate themselves to their hosts by touching, nipping, and fanning the tentacles over a period of minutes to days, until they are immune to the anemone’s stinging tentacles. The clownfish receive protection from predators, while guarding their host from anemone-eating fish, keeping it clean of parasites, and attracting zooxanthellae with their waste. Experimental evidence finds that when a clownfish is given small and large pieces of food, it will consume the former and offer the latter to its anemone.

Clownfish have a unique hierarchy, based on size and sex. Groups consist of a dominant female, a breeding male, and 0 to 4 sexless non-breeders. The largest will be the dominant female, while the second largest is the breeding male. If the dominant female dies or otherwise disappears, the breeding male will become the new dominant female, while the largest non-breeder will become the new male. Thus, non-breeders must wait for their time to become breeders, since nearby anemones are occupied and they are too small to challenge the dominants. The dominant pair controls membership of the group and will drive away individuals when the anemone gets too full, particularly those that are close to them in size. Newcomers can control their growth rate so they can remain smaller than their immediate superior to avoid getting evicted, but not too small so as to never get a chance at rising in rank.

The Sabre-toothed Blennies of the genera Aspidontus, Meiacanthus, Petroscirtes, Plagiotremus, and Xiphasia have fang-like teeth with venom glands at their bases.

The False Cleanerfish (Aspidontus taeniatus) mimics the dance and appearance of the Bluestreak Cleaner Wrasse (Labroides dimidiatus). It mimics the cleanerfish to avoid predation, and may also use it to sneak up and bite the fins of other fish. This is usually only successful on juvenile fish who have not learned to tell the difference between the False Cleanerfish and the Bluestreak Cleaner Wrasse.