of Otocinclus: (O. affinis, O. flexilis, O. mimulus and O. xakriaba) are considered to be Batesian mimics of certain Corydoras species (C. diphyes, C. garbei, C. nattereri and C. paleatus, respectively). These species have bony plates of armor and strong, frequently venomous spines as defenses, making them less palatable; by mimicking these species in size and coloration, Otocinclus avoid predation. A unique form of insemination has been described in Corydoras aeneus. When these fish reproduce, the male will present his abdomen to the female. The female will attach her mouth to the male's genital opening, creating the well-known "T-position" many Corydoras exhibit during courtship. The female will then drink the sperm. The sperm rapidly moves through her intestines and is discharged together with her eggs into a pouch formed by her pelvic fins. The female can then swim away and deposit the pouch somewhere else alone. Because the T-position is exhibited in other species than just C. aeneus, it is likely that this behavior is common in the genus. In the aquarium The genus is well known among aquarists for its many ornamental species. They are well suited to tropical freshwater community aquariums, as they get along well with other species and are not aggressive. Corydoras are quite timid and peaceful and are recommended to be kept in shoals of four to six or more. Corydoras are mostly bottom feeders, so they should be offered sinking pellets as well as supplements of live and frozen foods. If flake foods are used, care should be taken to prevent all food from being eaten by faster moving fish at the higher levels of the tank. Most Corydoras prefer soft, acidic water. They can, however, tolerate a wide range of water conditions, including temperatures that are cooler than tropical. They do not do well in fish tanks with high nitrate levels. This ion leads to the infection of the barbels, which will shorten and become useless. The barbels may also be affected by constant contact with a sharp substrate. Contrary to popular belief, these fish can be kept in a tank with gravel, as long as there are no sharp edges on the gravel without affecting their barbels, although they do prefer sand substrate. They are more likely to thrive if there is an open area of substrate on the bottom of the tank where they can obtain submerged food. It is a