Characins
The group of characins is much more diverse than most people think. Tetras are not the only characins, there are lots of them. Characins and catfish are the only fish that have an adipose fin, a small fleshy fin behind the dorsal fin.
An adipose fin on a corydoras. Not a great picture.
Smaller Tetras
These fish are all under 3 in. Tetras are all schooling fish. They like warmer temperatures and a ph that is slightly acidic. Tetras are great fish for community aquariums. The neon tetra is probably the most popular aquarium fish. Cardinal tetras are extremely similar to neon tetras. The black neon tetra and the glowlight tetras are like a neon tetras but a different colors. The serpea,pristella,black widow,ember, bleeding heart,lemon,black phantom, red phantom, and emporor tetras are all a little over 2 inches long. The columbian blue tetra is a relatively new discovery, and it gets 3 in. long. Penguin tetras are 3 inch fish that swim at an odd angle. I will add some more tetras soon.
The top ones are Neon Tetras. The bottom one is a bad picture of a pristella tetra but a good picture of the catfish in the back.
Larger Tetras.
These tetras like the same water conditions as the smaller tetras. Larger tetras are just as peaceful as their smaller relatives. Be sure to keep them in a school. All of these tetras are harder to find and more expensive than most tetras, but most of them are worth tracking down. These fish can get 4 in. or more in length. The easiest one to find is probably the red eye tetra. This hardy fish can get up to 4 inches, but it rarely gets that big. The congo tetra is another 4 inch tetra you might see for sale. Red congos are a more attractive but harder to find version of the congo tetra. The blind cave tetra is a 4in. and pale white tetra with no visible eyes. The 6in. bucktooth tetra is not a community fish because it eats the scales of other fish.Those are the only large tetras you will see in stores.
Hatchetfish
Hatchetfish are very strangely shaped. They look like a handleless hatchet. Hatchets are mostly peaceful and hardy fish. They like the same water conditions as tetras. These fish are amazing jumpers, so keep their tank well covered. Some hatchetfish prefer being in a small school. There are a few different species. The most common hatchet is the silver hatchetfish, which can get to 3 in. The slightly less common but more attractive marbled hatchet only gets to 2in. The transparent glass hatchetfish is the smallest, at only 1 inch. Spotted hatchets are the rarest hatchets, and are about 2 in. long. You won't find any other hatchetfish in stores.
My hard to photograph marbled hatchetfish.
Pencilfish
These are some of the most peaceful aquarium fish. They enjoy warm and slightly acidic water. Most pencilfish like to be in a small school of about 3 fish. All of these fish are under 3 inches. Diptail penilfish, also known as harisson's pencilfish, are the largest pencilfish, at 2.5 in. The dwarf pencilfish is the smallest pencilfish, with a length of only 1.5 inches. Three lined pencilfish are 2 in. fish with beautiful red splotches. Those are about all of the pencilfish usually seen in stores.
A diptail pencilfish. Its only an inch long.
Piranha
As most people think, these are NOT a community fish. They like warm and acidic water. These are hardy fish, and they are often breed in aquariums. Live feeder fish are not needed because these fish will eat frozen meat. Watch your fingers at feeding time. Piranhas can get large and are active and sometimes schooling fish, so they need a large tank. There are 2 species on general sale. DO NOT CONFUSE PIRANHAS WITH PACUS!!!. The red pirahna can get to 10 in. long, and it is probably more attractive than the black piranhas. Black piranhas are the same size as reds but you can tell the difference because the blacks have spots. That is some info on piranhas.
Pacus and Silver Dollars
These are all active, large,schooling fish. They like the same water conditions as piranhas. Pacus and silver dollars are similar to piranhas but they are mostly vegetarians. The pacu needs a huge aquarium because it can get over 2 feet long and 2 feet high. It likes to eat nuts and vegetables. There are a few different kinds of silver dollars, but they all can get 6 inches long and are schoolers. The different kinds are normal silver dollars, red hook silver dollars, and barred silver dollars. That is some info on pacus and silver dollars.
The not often seen barred silver dollar.
Headstanders
These fish are mostly attractive fish, but some get large and aggressive. They like warm acidic water. Most headstanders are very hardy. They swim with their heads pointed downward.One of the smallest and most peaceful headstander species is the 5 inch spotted headstander. The glass headstander looks very mean, but it is actually a very peaceful 5 inch fish. Striped headstanders can get to 7inches but they rarely get that big. The largest headstander is the 12 inch banded leporinus, which is often very aggressive. Marbled headstanders are rarely seen 6 in. fish.
A marbled headstander almost headstanding.
Distichodus
Distichodus are peaceful and attractive fish, but they get very large. They like warm water and the ph doesn't matter as long as you avoid the extremes. There are 2 species on general sale. The short nosed distichodus is the largest, at almost 3 feet. The long nosed distichodus is much more manageable, at only 16 inches.
Pike and Gar characins
These are the main predators of the characin world. They're not community fish. The water these fish like is the same as the tetras. The gar characin is the largest one, at 33 in. The rocket gar is much smaller, at only 10 inches. Asian needlenose gars are 7 inches when full grown. They may not be characins but they fit in this category. Pike characins are a foot long, a somewhat small size for pike characins. Striped fin eaters are 8 in fish that like to eat the scales and fins of other fish. Those are all of the pike and gar characins.
