| Pencil fish | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Lebiasinidae |
| Genus: | Nannostomus Günther, 1872 |
Nannostomus (from the Greek: nanno = small, stomus = mouth) is a genus of fish belonging to the Lebiasinidae family of Characins. All of the species in this genus are known as Pencil Fish or Pencilfish, several of which have become popular aquarium fish due to their attractive coloration, unique shape and interesting demeanor.
Contents |
The genus, Nannostomus, was first erected by Günther in 1872 with the type species, Nannostomus beckfordi. In 1876, Steindachner described three more species, Nannostomus unifasciatus, Nannostomus eques (pictured below) and Nannostomus trifasciatus (pictured above). In 1909 Eigenmann described Nannostomus marginatus and Nannostomus harrisoni. These first six species to be described have been popular with aquarists since the early twentieth century, in part due to enthusiastic articles written about them, and compelling photographs taken of them, by William T. Innes that were published as early as 1933. Over the years, the genus was split by subsequent authors into other genera including Poecilobrycon and Nannobrycon. After nearly a century of debate on the subject, Dr. Stanley H. Weitzman and Dr. J. Stanley Cobb restored earlier taxonomy and expanded upon it, unifying all species under Nannostomus in 1975. This comprehensive revision of the genus has now been widely accepted. Dr. Weitzman is also responsible for the description of five of the more recently introduced species, Nannostomus marilynae, Nannostomus limatus, Nannostomus nitidus, Nannostomus britskii and Nannostomus anduzei. Eighteen species are now known to science, Most of which are also known to aquarists. Several other unidentified Nannostomus have been imported over the years, many found as bycatch with other small characins, but their taxonomic status is yet to be determined.
Most species are slender, pencil-shaped fish ranging in size from under 1" to approximately 2" in length. N. marginatus, N. rubrocaudatus and N. mortenthaleri possess a shortened, blockier outline reminiscent of pencil stubs. All but one species, Nannostomus espei, possess one to five horizontal black or brown stripes with gold or silver iridescence appearing dorsal to the primary stripe. Most also display red, orange or maroon highlights in their fins, and many have flashes of these colors on their flanks as well. The recently described species, N. mortenthaleri and N. rubrocaudatus, are especially vividly colored. For N. espei alone, horizontal stripes are only weakly present and are supplanted by five dark comma-shaped blotches. This pattern is assumed by other species at night, but only N. espei displays the pattern permanently and in daylight. The adipose fin is present in some species and absent in others, while in certain species, Nannostomus eques for example, it may be present or absent within the species. All swim in a horizontal attitude except Nannostomus unifasciatus and Nannostomus eques, which assume an oblique, 'snout-up' posture. There is a range of sexual dimorphism in the genus, it being clearly evident in several species with males being more brilliantly colored, especially with regard to color present in the fins, and far less evident in other species. However, a reliable indicator of gender for most of the species rests in the anal fin of adult males which is enlarged and elongated (as in N. espei, N. eques et al.) and/or the anal fin of males is more colorful (as in N. harrisoni, N. marginatus et al.). The popular aquarium species, Nannostomus trifasciatus, is an exception in this regard.
The genus has a vast distribution in South America, from Colombia, Venezuela and the Guyanas in the north, to the southern Amazon basin and Bolivia in the south, to Peru in the west and Belem, Brazil in the east. Several of the individual species have a distribution nearly as vast. As a result, many of the species are polymorphic and manifest marked color variations depending on the population. Over the years, some of these color variants have been erroneously described as separate species. Such names as 'Nannostomus ocellatus', 'Nannostomus anomalus' and 'Nannostomus auratus', among many others, are now known to be junior synonyms to the various species. To date, only two species, Nannostomus beckfordi and Nannostomus harrisoni, have been commercially raised for the aquarium trade in fisheries, mostly in Asia. All of the remaining species that find their way to home aquaria are wild-caught from South American waters.
Nannostomus thrive in home aquaria when provided with soft, moderately acidic water, low nitrate levels and temperatures in the range of 72F to 82F. The addition of aquatic plants, including floating varieties, is recommended. The latter will reduce the likelihood of the fish jumping, which is a common occurrence for some of the species, especially N. espei and N. unifasciatus. They should be kept in schools of at least six. If kept in a community aquarium, the best tankmates are other species of Nannostomus, small peaceful characins and corydoras. Aquaria with strong water current, large tankmates, or swift-moving species are contraindicated. If kept in a thickly planted single-species aquarium with the above water parameters, most species will spawn, eggs will not be eaten, and the fry will be found among the floating plants. Baby brine shrimp, live or frozen, and other small-sized foods are required for both fry and adults. Nannostomus are also avid biofilm grazers and, for most of the species, algae is an under-reported staple of their diet. In most species the males will establish small territories and defend them. Their defensive actions are usually harmless but, in two species, N. mortenthaleri and N. trifasciatus, antagonistic behavior directed at conspecifics can have deleterious results if sufficient space and plant cover are not provided. Once acclimated to the aquarium, and provided with conditions to their liking, Nannostomus are hardy and have a firm grasp on life, often living for five or more years.