Meristics is an area of

ichthyology Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish ( Chondrichthyes), and jawless fish ( Agnatha). According to FishBase, 33,400 species of fish had been described as of Oct ...

and

herpetology Herpetology (from Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians ( gymnophiona)) and ...

which relates to counting quantitative features of

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

and

reptiles Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchoceph ...

, such as the number of fins or scales. A meristic (countable trait) can be used to describe a particular

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of fish, or used to identify an unknown species. Meristic traits are often described in a shorthand notation called a ''meristic formula''. Meristic characters are the countable structures occurring in series (e.g.

myomere Myomeres are blocks of skeletal muscle tissue arranged in sequence, commonly found in aquatic chordates. Myomeres are separated from adjacent myomeres by connective fascia (myosepta) and most easily seen in larval fishes or in the olm. Myomere c ...

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

fin ray Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

s) in fish. These characters are among the characters most commonly used for differentiation of

and

populations Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...

. In the

salmonids Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whit ...

, scale counts have been most widely used for the differentiation of populations within species. In

rainbow A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...

and

steelhead Steelhead, or occasionally steelhead trout, is the common name of the anadromous form of the coastal rainbow trout or redband trout (O. m. gairdneri). Steelhead are native to cold-water tributaries of the Pacific basin in Northeast Asia and ...

trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...

the most notable differences among populations occur in counts of scales. Meristic characters are used in many other fields, such as in

botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...

or in

zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, an ...

. Meristic comparison is used in

phenetic In biology, phenetics ( el, phainein – to appear) , also known as taximetrics, is an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary re ...

and

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analysis.

Meristic analysis

A meristic study is often a difficult task, as counting the features of a fish is not as easy as it may appear. Many meristic analyses are performed on dead fish that have been preserved in alcohol. Meristic traits are less easily observed on living fish, though it is possible. On very small fish, a microscope may be required. Ichthyologists follow a basic set of rules when performing a meristic analysis, to remove as much ambiguity as possible. The specific practice, however, may vary depending on the type of fish. The methodology for counting meristic traits should be described by the specialist who performs the analysis.

Meristic formula

A meristic formula is a shorthand method of describing the way the bones (rays) of a

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartil ...

fins A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

are arranged. It is comparable to the

floral formula A Floral formula is a notation for representing the structure of particular types of flowers. Such notations use numbers, letters and various symbols to convey significant information in a compact form. They may represent the floral form of a part ...

for flowers. Spine counts are given in Roman numerals, e.g. XI-XIV. Ray counts are given in Arabic numerals, e.g. 11–14. The meristic formula of the dusky spinefoot (''Siganus luridus'') is: D, XIV+10; A, VII+8-9; P, 16–17; V, I+3+I; GR, 18-22 This means the fish has 14 spiny rays (bones) in the first part of its

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

(D), followed by 10 soft rays. A is the anal fin, P represents the

pectoral fins Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

(near the gills and eyes), V represents the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two ...

s, and C is the caudal fin or tail (not indicated in this example). GR means gill raker count (see below).

Vertebral counts

The number of bones in the backbone is a feature which can also be used to classify fish species. Usually all the

are counted. Vertebral counts may be split into abdominal (those associated with the body cavity) and caudal (tail) vertebrae. If there are sutures in the urostyle, components are counted, otherwise the urostyle is usually counted as one vertebra.

Gill raker counts

The number of gill rakers on the first

gill arch Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...

can also be used to identify a fish species. Rakers are counted for the upper and lower limbs of the gill arch, and a raker at the joint of the upper and lower limbs is counted as of the lower. Counts for the upper and lower limbs are separated by a + sign and ranges are bracketed, e.g., GR: 3 + (4-5).

References

External links