#perciformes

Classification of this group has long been controversial, with various families being placed in and out of Perciformes depending on the study. Only in recent decades, with the advent of molecular phylogenetics, has the classification of the family been largely resolved. Yay fish taxonomy! Despite many families moving out, and into, Perciformes, it still remains one of the largest and most diverse vertebrate orders.

The anthias of the family Anthiadidae (image 1) are some of the most vibrant, colorful fish in the world. They can shoal by the thousands, but typically live in harems of one dominant male, 2-12 females of varying rank, and 0-2 non-dominant males. Most anthias are protogynous hermaphrodites. These anthias are born female; if the dominant male dies, the largest female of the group will often change into a male to take its place. This may lead to squabbling between the next-largest male, who will want the opportunity to advance in hierarchy, and the largest female.

The beautiful Sea Goldie (Pseudanthias squamipinnis) is known for its marked sexual dimorphism. Males are a dark fuchsia with a red patch on their pectoral fins, and sport elongated rays on their tail and dorsal fin. Meanwhile, females are bright orange/gold with violet “winged eyeliner”. Truly a creature that took “cartoon animal sexual dimorphism” to heart.

(male Sea Goldie)

(female Sea Goldie)

Many groupers (see gif above) are threatened by overfishing. The critically endangered Nassau Grouper (Epinephelus striatus) is fished both commercially and for sport.

Soapfish (subfamily Grammistinae) secrete a poisonous toxin as a defense mechanism. These secretions apparently resemble lathered soap and are the basis for their common name.

The European Perch (Perca fluviatilis), the type species of this order, is Finland's national fish. It is also pictured in emblems of several European towns and municipalities, such as Bad Buchau, Gröningen, and Schönberg, Plön.

Icefishes of the families Nototheniidae and Channichthyidae live where the Antarctic and sub-Antarctic waters of the Southern Ocean average −1 to 4 °C (30–39 °F). As an adaptation to the cold, most species of these regions produce antifreeze glycoproteins to prevent the formation of ice crystals in blood and other body fluids.

In February 2021, scientists discovered and documented a breeding colony of Jonah's Icefish (Neopagetopsis ionah), estimated to have 60 million active nests across an area of approximately 92 square miles at the bottom of the Weddell Sea in Antarctica. The majority of nests were occupied by one adult fish guarding an average of 1,735 eggs in each nest.

All species of scorpionfish (family Scorpaenidae) have venomous “stingers”, sharp spines similar to hypodermic syringes, to inject toxins. This venom is neurotoxic and is among the most toxic venom produced by fishes. The most venomous of these is the Reef Stonefish (Synanceia verrucosa). The spines on its back produce a venom which can cause severe pain, shock, paralysis, and tissue death in humans.

The Red Velvetfish (Gnathanacanthus goetzeei) sways back and forth with the swell in a similar manner to the kelp fronds they live among, enhancing their camouflage. Their brilliant red color seems counter-intuitive to this camouflage, but it appears dull within the caves and crevices at depths down to 55 m (180 ft) that this fish lives in.

The Coralline Sculpin (Artedius corallinus) lives in intertidal areas. An individual may have a “home pool” it retreats to at low tide, but will follow advancing tidewaters to forage in pools farther up the beach.

The Blob Sculpin (Psychrolutes phrictus), best known for falling apart on a molecular level when brought to the surface due to their loose, gelatinous skin, exhibits complex nesting behaviors complete with egg guarding. Blobfish have been seen gathering in large numbers to lay their eggs in a single surrounding nesting area. The number of eggs laid within one nest can range from 9,000 to 108,000. It is believed that as the female blobfish hover around the nests they also clean them and remove any sand or dirt.

The Alligatorfish (Aspidophoroides monopterygius) is named for the alligator-like scutes down its back.

Lumpsuckers (family Cyclopteridae) (image 4) are named for their nearly spherical bodies and modified pelvic fins, which have evolved into adhesive discs. The fish uses these discs to adhere to substrate. One species (Cyclopterus lumpus) is targeted commercially for its roe (eggs) and it is also caught from the wild to provide broodstock for the aquaculture industry, where it is used as a cleaner fish to remove sea lice from salmon farms. This is likely what the fish in the viral “very beautiful, very powerful” video were being bred for.

All Stickleback (family Gasterosteidae) species show similar, unusual mating behaviour. The male will construct a nest from weeds held together by spiggin, a kidney secretion, then attract females to the nest. Courtship typically involves a zig-zag “dance” where the male approaches the female in an erratic side-to-side pattern, and pricks her abdomen with his spines. The female will lay her eggs inside the nest, where the male fertilises them. The male then guards the eggs, and may continue to guard the fry after they hatch. This large investment in both the nesting site and guarding of the eggs limits the number of females a male can mate with, however males may spawn multiple times, though in some species the males die following spawning.

The Three-spined Stickleback (Gasterosteus aculeatus) has long been a subject of scientific study for many reasons. It shows great morphological variation throughout its range, allowing scientists to study evolution in an observable timeframe. This has been central to the field of eco-evolutionary dynamics. Eco-evolutionary dynamics is an area of study investigating how ecological processes (e.g., population dynamics, community interactions, and nutrient cycling) affect how populations evolve, and in turn, how these patterns of evolution feed back to affect ecological processes. Three-spined Stickleback are particularly useful for studying eco-evolutionary dynamics because multiple populations have evolved rapidly and in predictable, repeated patterns after colonizing new environments. These repeated patterns of evolution allow scientists to assess whether the impacts of stickleback evolution on ecological processes are reproducible. Behavioral research has also shown that sticklebacks display distinct personality traits, specifically in the area of taking a risk, and, can be considered “bold” or “shy.” These personality traits were determined to directly influence if they would lead a group, and if discouraged, attempt to lead again.

Wolffishes (family Anarhichadidae) are one of the few animals able to feed on sea urchins, which they crush with their powerful jaws and sharp teeth.

Despite their fearsome appearance, Wolf Eels (Anarrhichthys ocellatus) (image 3) are generally curious and non-aggressive towards humans, though they may inflict painful bites defensively. Male and female Wolf Eels mate for life and inhabit a cave together. Both parents will guard their eggs, taking turns to leave the cave to feed.

The Monkeyface Prickleback (Cebidichthys violaceus) is capable of living out of water (under algae) for extended hours at a time and is able to breathe air.