WildNothos
THE NOTHOBRANCHIUS SITE
INTRO - DISCOVERY & EARLY HISTORY - DISTRIBUTION & BIOGEOGRAPHY - ECOLOGY & BIOTOPE - LIFE HISTORY & REPRODUCTION - MAINTENANCE & BREEDING - TAXONOMY & SYSTEMATICS
Taxonomy and Systematics of Nothobranchius Fishes
Taxonomy is as old as the language skill of mankind. It has always been essential to know the names of edible plants or dangerous animals, in order to communicate acquired experiences to other members of the family and the tribe.
Species are individuals in the nature, they participate in natural processes, they change over time, they have origin and may give rise to other species through speciation and they will have an end in form of extinction. However, it has not always been seen like this…
In Western scientific taxonomy, already the ancient Greeks have been interested in the questions around origin and evolution. Thales stated that all things originated from water and Anaximenes declared the air as the principle of all things. The philosopher Aristotle believed in spontaneous generation, meaning that all living things arose from non-living sources. Aristotle classified all living organisms hierarchically in his great scala naturae with plants at the bottom, animals and humans on the top of creation, each becoming progressively more perfect in form.
Darwin’s Theory of Evolution represented a major milestone when in 1859 he published 'The Origin of Species' which theorised that all animals evolved by a process of natural selection from more basic life forms. According to his theory, adaptations or traits occur naturally in a population due to mutation. Evolution occurs as the more successful adaptations become dominant, and former traits are abandoned by the natural selection process. The groundwork for his study was certainly supported by analyses of fossils, which are remains of organisms from the past and usually having somewhat different from currently known species.
Taxonomy is the theory and practice of classifying the orderliness of nature in a worded system. Species that should be recognized as taxonomically distinct, can be described by following the rules set out in the Code by the International Commission on Zoological Nomenclature. A description has to be published in a permanent, duplicable form that is available to others, it has to be clearly stated as a new name, it has to be published within the context of the binominal nomenclature system, and it must be established on a type specimen that is the name-bearing key reference specimen. This museum specimen, called holotype, is designated to forever serve the standard of reference for the new species. In the system of binomial nomenclature formalized by Linnaeus, the italicized name of a species consists of the capitalized name of the genus it is placed in, plus the lowercase species epithet.
Several approaches can be used to study the distinctions and relationships among fishes, which include morphometrics, meristics, anatomical traits, colour patterns, karyotypes, molecular methods, etc.
Morphometrics and Meristic traits
When attempting identifications or conducting taxonomic studies on fishes it is often necessary to conduct certain measurements of body parts and counts in order to compile descriptive or analytical data or make choices in a taxonomic key. Morphometrics is the assignment of quantities to biologic shapes, so it is the empirical fusion of geometry with biology. Morphometric characters refer to measurable structures such as standard length, head length, fin length, or ratios between such measurements. Locations for making these counts and measurements are illustrated in the Figure below. By convention, these are made on the left side of the fish whenever possible.
Morphometric measurements used for my studies on Nothobranchius:
1, standard length; 2, predorsal length; 3, head length; 4, snout to eye end length; 5, postorbital length; 6, snout length; 7, vertical eye diameter; 8, suborbital depth; 9, head depth from the occiput to the lower head surface; 10, body depth at anterior base of pelvic fins; 11, dorsal fin base length; 12, smallest caudal peduncle depth; 13, utmost caudal fin length; 14, caudal peduncle length; 15, anal fin base length; 16, prepectoral length; 17, prepelvic length; 18, preanal length; 19, total length; 20, interorbital width; and 21, head width.
Horizontal measurements are typically made from the tip of the snout. Standard length is measured to the posterior edge of the hypural plate.
Meristics:
Meristic characters include almost any countable structure, including scales, fin rays, gill rakers, and more. The number of scales count in the mid-longitudinal series is defined as the number of scales between the upper attachment point of the opercular membrane and the base of the caudal fin. Excluded are the small scales posterior to the hypural junction. The number of transverse scale count is the number of scales in a diagonal scale row, starting ventrally in the front of the anal fin and reaching up to, but not including, dorsally the scale on the dorsal midline in the middorsal row. The number of circumpedunclar scales is counted around the caudal peduncle at the narrowest level of the caudal peduncle. The visible rays of dorsal and anal fins are counted.
Sense Organs
The sensory systems of fishes are necessarily quite different from those of terrestrial vertebrates. The cephalic lateralis system is instrumental in detection of sound or vibrations. The canals of the head and lateral line are equipped with cells called neuromasts which have hairlike cilia oriented in such a way as to detect directionality of vibrations. This information is transmitted directly to the brain via nerves which lie in proximity to the canals.
Frontal squamation pattern and cephalic sensory system
Dorsal view of head: an, anterior neuromasts; ap, anterior preorbital level; as, anterior supraorbital level; n, nostril; pp, posterior preorbital level; ps, posterior supraorbital level; A-G, frontal scales.
Skeleton
Fish swims and maneuvers by the mechanics of associated bones and muscles. Adaptive variation in bone form among species bears important taxonomic characters for fish identification and systematics. These characteristics include vertebral number, position and compositions of fins, jaw structure, etc.
Small fish specimens, such as Nothobranchius, can have skeletons prepared via clearing and staining. This process renders the flesh and muscle tissues invisible and the bone red. Cartilage can be stained blue. The general methods follow Taylor and van Dyke (1985); a specimen here beside stained for bones only.
Systematics
Fish systematics is the formal description and organisation of fish taxa into systems. It is complex and still evolving. Nothobranchius fishes belong to Teleosts, one of three infraclasses in class Actinopterygii or ray-finned fishes, and which is the overwhelmingly dominant infraclass of fishes with nearly 30,000 species, covering about 96 percent of all extant fish species. They are further organized in the order of Cyprinodontiformes, which comprises mostly small, freshwater fish, many of them popular aquarium fish, such as killifish and live-bearers.
The name Nothobranchius is composed of the Greek words νόθος (nothos = false-) and βράγχιος (branchion; gill), and refers as false gills to the open preopercular neuromast system which gives the impression of an additional gill opening. The genus Nothobranchius includes more than 90 species whereas a number of populations are under preparation for description. Furthermore, new species are often found during collecting trips, so the number of species is expected to be increased in the future.
The species are currently organized in different sub genera or species groups, such as Adiniops Myers, 1924; Zononothobranchius Radda, 1969; Aphyobranchius Wildekamp, 1977; and Paranothobranchius Seegers, 1985, or the N. brieni species-group, N. neumanni species-group, etc. These taxa have traditionally been defined on the basis of shared elements of male colour patterns and morphological characters. Several molecular studies, that have been published lately or are under preparation, will serve for supporting or modifying the current classification.
Figure: Phylogenetic tree based on sequences of the protein-coding ND2 mitochondrial gene and Bayesian analysis. Support values are posterior probabilities.
originally published in:
Nagy, B., F. P. D. Cotterill & D. U. Bellstedt. 2016. Nothobranchius sainthousei, a new species of annual killifish from the Luapula River drainage in northern Zambia (Teleostei: Cyprinodontiformes). Ichthyological Exploration of Freshwaters, 27 (3): 233–254.
I found it and I named it, being versed
in taxonomic Latin; thus became
godfather to an insect and its first
describer — and I want no other fame.
Vladimir Nabokov - On Discovering A Butterfly. The New Yorker, May 15, 1943 P. 26