Characins have teeth & an adipose fin behind the dorsal fin. The fish have a number bones going between the inner ear to the swim bladder. The point of this is their increased ability to hear. As you will see below, one fish has eyes that are covered but fortunately to them, they are able to navigate.
Black Neon Tetra (Hyphessobrycon herbertaxelrodi) is from Brazil & can grow to 4cm (c. 1.5") whereas in the tank, they reach only 2.5cm (1"). Due to their colour, the fish are best seen in a tank with dark substrate. They enjoying swimming & therefore are better with others of their own. If the fish feels unwell, their colour drops.
As its name says, Blind Cave Fish (Astyanax fasciatus mexicanus) is blind! They live in caves at Texas, Mexico (as their name suggests) and through to Panama & they cannot use their eyes. They use the lateral line, which creates a highly developed sensory system. In the wild they can grow to 10cm (4") but in a tank 5cm (2").
Cardinal Tetra (Paracheirodon axelrodi) is in River Negro & its tributaries, which are in Brazil & last up to 3 years. They can grow to 5cm (2"), but in a tank slightly more than 2.5cm (1"). These equally show well in tank with a dark substrate & also not too much lighting. Reproduction in a tank is very difficult. As they can cope with tap water, they prefer soft water.
Sadly, I have not got a picture of a Diamond Neon Tetra & equally not too much knowledge. I know they are the same as Neon Tetra however the colour blue only covers the top of the head. They are smaller than the Neon Tetra & unfortunately, they were eaten within a few weeks.
Flame Tetra (Hyphessobrycon flammeus) comes from around Rio de Janeiro, Brazil. They grow to 4cm (c. 1.5") but in a tank it is less than 2.5cm (1"). They are happy with well lit tanks. It is true that their colours are not shown too well in a shop. Once I bought mine & placed them in the tank, an hour later, they were showing their colours.
Glowlight Tetra (Hemigrammus erythrozonus) is fantastic in a dark substrate, especially if males display their luminous orange band. Their natural habitat is the Essequibo River in Guyana & their size is 4cm (c. 1.5"), their size in a tank is 2.5cm (1"). They, like other tetras, eat flakes, frozen food & such things as bloodworms & grindal worms.
Due to its shape, Marbled Hatchet Fish (Carnegiella strigata) lives just under the surface. They do jump & sadly without me not closing the lid, they jumped & landed out of the water. The jumping is done through well-developed pectoral fins. They are sociable & in the wild live in Peru & Guyana. Their size in wild can be 5cm (2") but 2.5cm (1") with mine.
Neon Tetra (Paracheirodon innesi) is probably one of the best-sold fish. Once I read they can survive for 10 years, but on further investigation, they live 4 years in the wild, which is Eastern Peru. Another thing I have read is about putting them in with such things as Angels. When Neon Tetra is small & Angels large, they will be eaten.
Rummy Nose Tetra (Hemigrammus rhodostomus) come from lower Amazon & can reach 5cm (2"), yet less so in a tank. Out of the tetras, these are slightly more difficult to keep than the others, however I have not had any problems. The only notice I have seen was the colour of the head by it dropping the red. I suspect that was fear for them, as the colour came back after a while.
Like nearly all the Characins, Silver Tip Tetra (Hasemania nana) needs to be kept in shoals. Shoals, to them, equals safety & as they are friendly fish, it keeps them happy. The habitat is Brazilian rivers & also countries near Brazil. The rivers tend to be darken water with the colour coming from rotting vegetates. Their natural size is 5cm (2") with their colours being brighter in males but females are plumper in size.
X-ray Tetra (Pristella riddlei) is often called Pristella Tetra. The body of the fish has a transparent body & this means that the spine can be seen but the internal organs being covered by a silvery sac. Like all tetras, the female is plumper than the male however breeding is difficult in tanks. In the lower Amazon, they can grow to 5cm (2").
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