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Astyanax mexicanus

Astyanax mexicanus
Blind Cave Tetra
The Mexican tetra or Blind Cave Fish (Astyanax mexicanus) is a freshwater fish of the characin family (family Characidae) of order Characiformes. The type species of its genus, it is native to the Nearctic ecozone, originating in the lower Rio Grande and the Neueces and Pecos Rivers in Texas as well as the central and eastern parts of Mexico.
Growing to a maximum overall length of 12 cm, the Mexican tetra is of typical characin shape, with unremarkable, drab coloration. Its blind cave form, however, is notable for having no eyes and being albino, that is, completely devoid of pigmentation; it has a pinkish-white color to its body.
This fish, especially the blind variant, is reasonably popular among aquarists.
A. mexicanus is a peaceful species that spends most of its time in the mid-level of the water above the rocky and sandy bottoms of pools and backwaters of creeks and rivers of its native environment. Coming from a subtropical climate, it prefers water with 6.0–7.5 pH, a hardness of up to 20 dGH, and a temperature range of 22 to 28 °C. In the winter it migrates to warmer waters. Its natural diet consists of crustaceans, insects, and annelids, although in captivity it is omnivorous. A. mexicanus is famous for its blind cave form, which is known by such names as blind cave tetra, blind tetra, and blind cavefish. Some thirty distinct populations of Mexican tetras live in deep caves and have lost the power of sight and even their eyes. These fish can still, however, find their way around by means of their lateral lines, which are highly sensitive to fluctuating water pressure.
The eyed and eyeless forms of A. mexicanus, being members of the same species, are closely related and can interbreed. Astyanax jordani, however, is another blind cave fish, independently and recently evolved from the sighted surface form, which is sometimes confused with the cave form of A. mexicanus. However, when born, the cave dwelling form of A. mexicanus has eyes. As they grow older, skin just grows over them and the eyes degenerate completely, because there is no need for sight in the pitch-black world of a cave. A. mexicanus only grows to a length of 12 cm in the recommended minimum of 30 US gallons. The blind cave tetra is a fairly hardy species. They are not picky on food, as they will eat anything from standard flakes to sinking carnivore pellets. Their lack of sight does not hinder their ability to get any and all food before it hits the bottom. They prefer subdued lighting with a rocky substrate, like gravel. It is recommended that the tank mimic their natural environment, so artificial or natural rock is highly appreciated. They become semi-aggressive as they age, but are by nature schooling fish, and a group of at least three is a good idea. However, it isn't imperative, as they can be kept as a single specimen. As stated earlier, they can get to their food rather swiftly, even more so than fish with the ability to see, so they aren't really good for a community, but one is OK for a semi-aggressive community. They are also incredibly fast, so catching them with the net is a chore in itself while conducting maintenance.

盲鱼在分类学上隶属于脂鲤科、墨西哥盲眼鱼属。它是一种非常美丽的观赏鱼,体长大约为12厘米,身披亮银色鳞片,所有的鳍部均呈奶油色。大约在数万年前,盲鱼的祖先被水流带到了只有很少光线或完全没有光线的地下洞穴内,随着漫长的岁月流逝,它的眼睛因无用武之地而退化,变成了今天的盲鱼。对于一般动物来说,没有眼睛简直是不能生活的,但盲鱼的眼睛虽然失去了它应有的作用,却能够依靠其它器官的特殊感觉来进行正常的生活。盲鱼在分类学上隶属于脂鲤科、墨西哥盲眼鱼属。它是一种非常美丽的观赏鱼,体长大约为8厘米,身披亮银色鳞片,所有的鳍部均呈奶油色。大约在数万年前,盲鱼的祖先被水流带到了只有很少光线或完全没有光线的地下洞穴内,随着漫长的岁月流逝,它的眼睛因无用武之地而退化,变成了今天的盲鱼。对于一般动物来说,没有眼睛简直是不能生活的,但盲鱼的眼睛虽然失去了它应有的作用,却能够依靠其它器官的特殊感觉来进行正常的生活。它是一种游速很快的鱼,能够自由自在地在水中游动,不会在游动撞上水草、石块或其它的鱼。也就是说,眼睛的退化并没有给它的生活带来什么不利的影响。 盲鱼又名无眼鱼、墨西哥盲鱼。鱼体呈长形,稍侧扁,尾鳍叉形,体长约 12 厘米。盲鱼体色呈乳白色,各鳍与体色一致并透明。这是热带鱼中体色最具个性的鱼。由于它在地下山洞中生活,眼睛退化,其他感觉器却特别发达。盲鱼刚孵出的幼鱼是有眼睛的,当幼鱼长到 2 个月左右,眼睛才逐步退化。盲鱼虽然没有眼睛,但在水中不会撞到其他物体,而且捕食能力一点不差,只要投入食物,盲鱼就立即发现,并游过来吃。