Danionin
The danionins are a group of small, minnow-type fish belonging to the family Cyprinidae. Members of this group are mostly in the genera "Danio", "Devario", and "Rasbora". They are primarily native to the fresh waters of South and Southeast Asia, with fewer species in Africa. Many species are brightly coloured and are available as aquarium fish worldwide. "Danio" species tend to have horizontal stripes, rows of spots, or vertical bars, and often have long barbels. "Devario" species tend to have vertical or horizontal bars, and short, rudimentary barbels, if present at all. All danionins are egg scatterers, and  breed in the rainy season in the wild. They are carnivores, living on insects and small crustaceans. Taxonomy. The grouping of fish now deemed danionins has been the subject of constant research and speculation throughout the 20th century. Nearly all the fish classed within the genera "Danio" and "Devario" were originally placed in the genus "Danio" upon discovery. However, in the first part of the 20th century, George S. Myers split them into three genera, "Danio", "Brachydanio", and "Daniops". The sole species within Myers' "Daniops", "D. myersi", has long ago been found to be a synonym of "Devario laoensis", but  his genus "Brachydanio" lasted for much longer, as it included most of the fish now classed as "Danio", whereas "Danio" included most of the fish now classed as "Devario". However, "Danio dangila" and "Danio feegradei", both of which had most of the characteristics of the "Brachydanio" (with the exception that they were much larger than "Brachydanio" species) were placed within "Danios". (Due to this and other misplacing, both "Danio" and "Brachydanio" were found to be paraphyletic by Fang Fang in 2003.). In 1941, H.M. Smith attempted to unite all the "Brachydanios" and "Danios" species into one genus on the basis  of a fish from Thailand, which was supposed to bridge the gap. He downgraded both "Danio" and "Brachydanio" into subgenera and erected a new subgenus of "Allodanio" with one member, "Allodanio ponticulus", but Myers later pointed out that "A. ponticulus" was actually a member of the genus "Barilius". The danionin group was thought to include "Parabarilius", "Danio", "Brachydanio", and "Danionella". In this scheme, danionins were distinguished from other cyprinids by the uniquely shared character of the "danionin notch", a large and peculiarly shaped indentation in the medial margin of the mandibles; this feature is not noted in rasborins, esomins, bariliins , or chelins. However, all of these categories at that time were informal. "Microrasbora" was not considered to be a part of the danionins, nor even closely related to "Danionella", a part of the danionins as understood at that time. In the late 1980s and 1990s, doubts grew about the validity of "Brachydanio", with species being referred to their original naming of "Danio", and Fang Fang determined that the genus "Danio", recognized up to that point, was paraphyletic. Fang Fang restricted "Danio" to the species in the ""D. dangila" species group", which at the time comprised nine species, including "D. dangila , D. rerio", "D. nigrofasciatus", and "D. albolineatus"; the remaining "Danio" species were moved to "Devario", which at this time included "D. malabaricus", "D. kakhienensis", "D. devario", "D. chrysotaeniatus", "D. maetaengensis", "D. interruptus", and "D. apogon". The only "Danio" species to have been consistently called "Danio" were "D. dangila" and "D. feegradei". As "D. dangila" was the first discovered "Danio" (or type) the name "Danio" had to remain with "D. dangila", which is why the vast majority of species were moved to "Devario". Also, the sister group to "Devario" was deemed to be a clade formed by "Inlecypris" and "Chela", and  more controversially, "Esomus" was found to be the sister group of "Danio". The relationships of "Sundadanio", "Danionella", and "Microrasbora" remained unresolved. The danionin notch was found to not supported to be a danionin synapomorphy. In another paper, "Celestichthys margaritatus" was described as a new species of the Danioninae. Apparently, it is most closely related to "Microrasbora erythromicron"; the other "Microrasbora" species differ significantly from "Celestichthys". The genus is identified as a danionin due specializations of its lower jaw and its numerous anal fin rays. Though it lacks a danionin notch, "Celestichthys" exhibits the "danionin mandibular knob", a bony process on  the side of the mandible behind the danionin notch or where the notch should be; it is perhaps diagnostic of danionins. This knob is better developed in males than females. The fish of Rasborinae almost invariably have anal fins with three spines and five rays. "Celestichthys" has three anal fin spines and 8-10 anal fin rays. Also, rasborins have the generalized cyprinid principal caudal fin ray count of 10/9, while all Asian cyprinids with fewer than 10/9 principal caudal fin rays are all diminutive species of Danioninae, including "Celestichthys", "M. erythromicron", "Danionella", and "Paedocypris". In 2007, an analysis of  the phylogenetic relationships of the recently described genus "Paedocypris" was published, placing it as the sister taxon to "Sundadanio". The clade formed by these two genera was found to be sister to a clade including many danionin genera, as well as some rasborin genera such as "Rasbora", "Trigonostigma", and "Boraras", making the danionin group paraphyletic without these rasborin genera based on these results. This paper considered the danionin genera to be within a larger Rasborinae. Also in 2007, another study analyzed the relationships of "Danio". These authors considered Rasborinae to have priority over Danioninae, suggesting that they have the same  meaning. Also, "Danio" was found to be the sister group of a clade including "Chela", "Microrasbora", "Devario", and "Inlecypris", rather than in a clade exclusively with either "Devario" or "Esomus" as in previous studies. This paper supported the close relationship of ""Microrasbora" erythromicron" to "Danio" species; however, this study did not include "Celestichthys", which was noted by Roberts as being likely to include "Erythromicron", but with further research needed. "Tanichthys" is often regarded as a danionin by aquarists and grouped as such in some older aquatic publications, but no scientific basis exists for this, a fact stated on numerous occasions  by Brittan and others. It is more closely related to the "Rasbora" species. The danionins can be classed as a subfamily Danioninae which is increasingly gaining credibility as a subfamily distinct from the Rasboriniae within the family Cyprinidae. However, in Nelson, 2006, Danioninae was listed as a synonym of Rasborinae. However, neither inter- nor intrarelationships among the "rasborins" has as yet been thoroughly analyzed. A number of the species have only been recently discovered, in remote inland areas of Laos and Myanmar, and do not yet have scientific names. They are listed as "Danio" or "Devario" sp "xxxx" within the  relevant genera and disambiguation pages. In the aquarium. They are generally active swimmers, occupying the top half of a tank and eat just about any type of aquarium food. They will not, however, generally eat plants or algae. Although boisterous and liable to chase each other and other fish, they are good community fish and do not generally attack each other or other fish, although they occasionally nip fins, and like most fish, eat eggs and any fish small enough to fit into their mouths. These fish are easily stressed by flowing water and bright light. They occur in stagnant  water with pH values between 3 and 5 caused by peat, which accumulates from a dense canopy. Generally, this also results in them being subtropical with temperatures of often being fine; they are good jumpers, so a tight-fitting lid is recommended. Common names given to danionin species. Since 2004, many new danionins have been discovered, which do not yet have scientific names and many other species, previously known only to the scientific fraternity, have become available in aquarist shops. This has predictably led to total confusion as to the naming of some fish, with some species having up to  five different common names in use and some common names being used for up to four different species. Danionin species scientific names. Individual danionin species are listed within the relevant pages for each genus, but many danionin species have been changed into different genera over the last decades, in some cases repeatedly; similarly, some species have been synonymised with other species and in some cases later unsynonymised, all of which has caused confusion.