This superorder contains about 28% of all fish species, and 68% of all freshwater species. Out of almost 8000 species, only 100+ are marine. All fishes in this group produce an alarm substance, also known as Schreckstoff. It is a pheromone produced when the skin is injured, alerting fellow nearby ostariophysans to the presence of danger, with the physiologic response known as the fright reaction. Some fishes do produce alarm substances but lack fright reactions.
Only containing the gonorhynchiforms, these fishes lack Weberian apparatuses/apparati.
This is technically the only order in Anotophysi, the outlier to Otophysi in the Ostariophysans. These fishes lack teeth, maybe because they wouldn't fit in their tiny mouths. These fishes have a primitive version of the Weberian apparatus, made of specialized bones to amplify sound transferred from the swimbladder to the ear; the actual Weberian apparatus is found in Otophysans.
This group is unified by the presence of the Weberian apparatus. The apparatus contains modified anterior vertebrae (known as Weberian ossicles) which transmit sound from the vibrating gasbladder to the inner ear.
One of the most diverse orders, there are over 3200, found mainly in Southeastern Asia, and no species found in Australia or South America. They differ from most other Ostariophysans in lacking an adipose fin near the tail.
Most of these species are carnivorous, and have an adipose fin as well. They tend to be similar in body shape to Cypriniformes.
Oh, Catfishes! Such a joy to fishermen everywhere, when you must remove them from the hook! They are quite the interesting group, I must say. I don't know what was trying to eat them in the past, but they have evolved way too many defense mechanisms. Catfishes have dorsal and pectoral spines, an unusual feature in the non-Acanthopterygii. Some may even have glands that produce a venom, causing an extremely painful sting that can result in death from certain species. The most defining feature of Siluriformes is the presence of barbels, although there can be anywhere from 1 to 4 pairs, and a few species lack them entirely. The barbels have chemosensory receptors, which the catfish uses to search for food on the bottom. Catfishes also lack scales, although some of them may have protection in the form of head armor. Siluriforms are found all over the world except Antarctica.
This order is made of the knifefishes, eel-like fishes that lack pelvic fins and have an anal fin that extends from below the head, alllllll the way to the tip of the tail. The anal fin is the main source of propulsion, allowing the fish to move both forwards and backwards. The anal opening is placed under the head or pectoral fins, because it must be forward of the anteriorly placed anal fin. The most interesting feature is the presence of electric organs, which are derived from muscle cells in most species but nerve cells in Aperonotids. Each species generates its own unique signal, which is thought to be used to navigate its environment, find food, and communicate. One species (discussed more below) uses its electric-generating capacity for other things as well.