# Meristics

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Area of zoology and botany

**Meristics** is an area of [zoology](/source/Zoology) and [botany](/source/Botany) which relates to counting quantitative features of animals and plants, such as the number of fins or scales in [fish](/source/Fish). A **meristic** (countable trait) can be used to describe a particular [species](/source/Species), 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. [myomeres](/source/Myomere), [vertebrae](/source/Vertebrae), [fin rays](/source/Fin_ray)). These characters are among the characters most commonly used for differentiation of species and [populations](/source/Population_(biology)). In the [salmonids](/source/Salmonids), scale counts have been most widely used for the differentiation of populations within species. In [rainbow](/source/Rainbow_trout) and [steelhead trout](/source/Steelhead_trout) the most notable differences among populations occur in counts of scales. Meristic comparison is used in [phenetic](/source/Phenetic) and [cladistic](/source/Cladistic) analysis.

## Meristic analysis

A meristic study is often a difficult task. For example, 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](/source/Fixation_(histology)) 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](/source/Ichthyologist) 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](/source/Bony_fish)'s [fins](/source/Fish_fin) are arranged. It is comparable to the [floral formula](/source/Flower#Floral_formula) for flowers.

Spine counts are given in Roman numerals, e.g. XI-XIV. Ray counts are given in Arabic numerals, e.g. 11–14.[1]

The meristic formula of the [dusky spinefoot](/source/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](/source/Dorsal_fin) (D), followed by 10 soft rays. A is the anal fin, P represents the [pectoral fins](/source/Pectoral_fins) (near the gills and eyes), V represents the [ventral](/source/Ventral_fin) or [pelvic fins](/source/Pelvic_fin), 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 [vertebrae](/source/Vertebrae) 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](https://en.wikipedia.org/w/index.php?title=Urostyle&action=edit&redlink=1), components are counted, otherwise the urostyle is usually counted as one vertebra.[2]

## Gill raker counts

The number of gill rakers on the first [gill arch](/source/Gill_arch) 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).[3]

## See also

- [Morphometrics](/source/Morphometrics)

## References

1. **[^](#cite_ref-1)** ["System glossary: ray"](http://www.fishbase.org/Glossary/Glossary.php?q=ray&language=english&sc=is). *Fishbase*. Retrieved 16 May 2016.

1. **[^](#cite_ref-2)** ["System glossary: Vertebral counts"](http://www.fishbase.org/glossary/Glossary.php?q=vertebral+counts). *Fishbase*. Retrieved 16 May 2016.

1. **[^](#cite_ref-3)** ["System glossary: Gill raker counts"](http://www.fishbase.org/Glossary/Glossary.php?q=gill+raker+counts&sc=is). *Fishbase*. Retrieved 16 May 2016.

## External links

- Chase, P. D. (2014) ["Meristics"](https://books.google.com/books?id=tYZqAAAAQBAJ&dq=Meristics&pg=PA171). In: Steven X. Cadrin, Lisa A. Kerr and Stefano Mariani (Eds) *Stock Identification Methods: Applications in Fishery Science*, second edition, pp. 171–184. Academic Press. [ISBN](/source/ISBN_(identifier)) [9780123972583](https://en.wikipedia.org/wiki/Special:BookSources/9780123972583).

- [Fish identification using meristics](https://web.archive.org/web/20110708043845/http://www.practicalfishkeeping.co.uk/content.php?sid=3063) *Practical fishkeeping*. 26 July 2010.

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