Styx Fish

MEMORY: This isn't a big issue. Very few fish have good learning skills. Most cannot learn to avoid lures that look nothing like what they see in nature. If learning to avoid neon colored objects on the water's surface that hooks you more than once says anything about their memory, then Styx fish would not need to have memory. Studies on fish learning show that most can learn to avoid an object with an appropriate danger stimulus. (Learning to swim to a safe side of a tank to avoid a shock that comes with a cork hitting the water.) The Yellow perch cannot even learn that. So Styx fish do not need memory skills.

SURVIVAL AND SENSES: If you feel the pollution of the Styx with corpses, blood, planar waste (from blood war weapons factories and failed magic potions), and various other lower planar filth is too much for the Styx fish to see, let alone survive in. You are mistaken. Like some species of catfish, Styx fish can survive high toxicity levels. In the worst places Styx fish can gasp air like lungfish. Styx fish in Acheron (where the Styx doesn't stay in a riverbed, but instead flows sideways over the cube until the river changes course further upstream) can get stranded without water. These fish can burrow into the scant river sediments (dried blood and such) until it turns metal, orcs/goblins dig them up, or the river returns. Some of these Styx fish cannot be petrified in the more detrimental parts of the plane; instead they lurk in the metal/stone until the water returns. Then they secrete an enzyme that eats through the metal/stone until they are free. Styx fish can have up to as many as seven senses.

SIGHT: Sight is the least important, because in most places the Styx's water is so murky that light doesn't make much of a difference. Those rare places that are relatively clear have visually acute fish. Some of which, like the archer fish, have eyes that can compensate for water/air distortion and accurately attack prey/victims that are not in the water. In the worst stretches of the Styx fish either develops bright lights, or lose sight entirely. Some species are completely eyeless. Others have light amplifying eyes like the walleye, dual (above the water/below the water) pupils like the four eyed fish, and eyes with phosphorescent patches behind them like the flashlight fish. Some say that a few Styx fish have unique eyes unlike those of fish on the prime such as raised or stalked eyes.

SMELL AND TASTE: To some catfish these are the most important senses. Sharks also rely heavily on smell. They can detect as little as one drop of blood per (I forgot the amount, it's been so long since shark week) drops of water. Many Styx fish, like some catfish, have tastebuds on their skin. In regions where non-toxic (to the fish) organic substances are abundant (near the mouth of the river of blood for example); Styx fish swim with their mouths open feeding on the ambient nutrients. Again, like catfish, Styx fish are sometimes drawn to scents that repulse humans (blood, rotting meat, etc.).

HEARING: Since sound travels better through water, Styx fish have excellent hearing.

TOUCH: Some Styx fish feel with barbels on their face.

ELECTROSENSE: Sharks can detect the electrical impulses from their prey. Some fish on the Amazon River can create their own electric guidance systems. Other species can detect this electric guidance and feed on them (one species of electric fish feeds almost exclusively upon the tails of other electric fish. They can regenerate their tails so it's a renewable resource.), the electric eel and torpedo ray go as far as to use their current as a defense/hunting weapon as well as guidance.

VIBROSENSE: Almost all fish have a lateral line running down their sides. This line detects vibrations in the water. The fish that feel these vibrations then act upon them (defense responses, attacking prey, etc.).

FEEDING STRATEGIES

FILTER FEEDERS: Instead of filtering plankton, some Styx fish filter blood and other organics from the river.

PREDATORS: Many Styx fish hunt down their prey with lethal precision. They often use built in luring methods such as, "fishing pole appendages", lights, fins that look like fish, and appearing as something of value (such as a portal key). Other Styx fish wait in ambush for their prey, or follow the bloodway armies.

HERBIVORES AND OMNIVORES: Since plants are either rare or dangerous in the lower planes, the herbivores tend to be rare (and often dangerous). The omnivores have the best of both worlds. These are most often encountered, as fish that don't care what they eat, not fish that eat both meat and plants (since plants are rare in many lower planes).

SCAVENGERS: The corpses of dead fiends feed many a fish.

PARASITES AND OTHER FEEDING TYPES: Lampreys and other bloodsuckers occur more often than one would think (especially with rivers of blood and bleeding dead fiends ending up in the Styx). Other fish are like the cookie cutter shark which uses it's unique mouth to cut out a nice circular slice from its victim.

CAMOFLAGE: Styx fish usually have protective coloration (those that don't tend to be toxic). Often looking weedy or rocky. Others change color like a chameleon due to chromatopores. Some blend in perfectly with the bottom, yet have toxic spines clueless people can step on.

BREEDING: Depending on the species Styx fish may or may not migrate to breed, lay eggs, change gender, or build nests. Any prime fish-breeding behavior is found in the Styx and a few extra ones with evil twists exist as well.