Meristics is an area of

zoology Zoology ( , ) is the scientific study of animals. Its studies include the anatomy, structure, embryology, Biological classification, classification, Ethology, habits, and distribution of all animals, both living and extinction, extinct, and ...

and

botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

which relates to counting quantitative features of animals and plants, such as the number of fins or scales in

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

. A meristic (countable trait) can be used to describe a particular

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, 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,

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

, fin rays). These characters are among the characters most commonly used for differentiation of species and populations. In the salmonids, scale counts have been most widely used for the differentiation of populations within species. In rainbow and steelhead trout the most notable differences among populations occur in counts of scales. Meristic comparison is used in phenetic and

cladistic Cladistics ( ; from Ancient Greek 'branch') 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 ...

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 in alcohol. Meristic traits are less easily observed on living fish, though it is possible. On very small fish, a microscope may be required.

Ichthyologist 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, 35,800 species of fish had been described as of March 2 ...

s 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 ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

's fins 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 (D), followed by 10 soft rays. A is the anal fin, P represents the pectoral fins (near the gills and eyes), V represents the ventral or

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

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 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