Fish Taxonomy and Systematics

Lecture 1:

Taxonomic systems

Our planet, earth, is occupied by diverse kinds of living organisms.

They live in various environments.

The world is estimated to have 5 - 30 million species of living organisms.

At present, about 2.5 million species of living organisms have been given scientific names.

Introduction

Over 1.5 million of them are animal species and out of which 750,000 belong to insect species alone.

Over 350,000 species of plants include algae, fungi, mosses and higher forms of plants.

Thus, the existence of different forms of a species or genus and diverse adaptations for, varied surroundings are referred to as “biodiversity”.

Introduction

Since the world has a vast range of organisms, identifying the useful, as well as harmful living beings is a need.

Differentiating, grouping and giving names to living things has been an ancient activity of every human culture.

Without proper classification it would be impossible to deal with enormous diversity of life forms.

Introduction

The initiation for evolving taxonomic systems was provided by Aristotle (384-322 BC) ‘father of biological classification’.

He emphasized that animals can be classified according to their way of living, actions, habits and body parts.

He observed insects, fishes, birds and whales.

The insect orders like Coleoptera, Diptera were created by him.

Introduction

For modern taxonomy, the first work was carried out by John Ray (1627 - 1705) of England.

He divided animals into those with blood and those without blood, gills, lungs, claws, teeth and other structures.

He provided the first good definition of the species as ‘a reproducing unit’.

Introduction

The great Swedish naturalist Linnaeus (Caroli Linnaei) (1707 - 1778) ‘father of taxonomy’.

He first introduced the hierarchic system, both in animal and plant kingdoms.

He followed four categories namely class, order, genus & species for the animal world.

His greatest contribution to taxonomy was the use of binomial nomenclature for all species of animals and plants.

Introduction

Michael Adamson (1727 - 1806), a French botanist, helped to develop a new type of taxonomy called ‘Numerical Taxonomy’.

Lamarck (1744 - 1829) arranged animals according to evolution.He displayed the groups of animals in the form of a branching tree.It was the beginning of the use of phylogeny in systematics.

Introduction

Cuvier (1769 - 1832) insisted that extinct fossil forms should be included in the table of classification.

He divided animals into four branches:

1.Vertebrata-fishes to mammals,2.Mollusca-mollusca and barnacles,3.Articulata-annelids, crustaceans, insects and spiders, and4.Radiata-echinoderms, nematodes and coelenterates.

Introduction

Charles Darwin in 1859, published his famous work ‘Origin of species’.

Due to the influence of evolutionary ideas, taxonomy was studied as an important evidence in favour of evolution.

The taxonomists were encouraged to learn that evolution theory of Darwin gave meaning to their classifying activities.

A large number of species were discovered and described.

Introduction

E. Mayr (1942) considered species as “groups of interbreeding natural populations”.

His book ‘New Systematics’ became a landmark in the history of taxonomy.

Morphological characters were studied along with other characters as behaviour, sound, ecology, genetics, zoogeography, physiology and biochemistry.

Thus taxonomy was transformed into ‘biological taxonomy’.

Introduction

Fish Taxonomy is basically the science of correctly naming fish species.

The term has often been confused with fish identification, which basically refers to the use of the latest taxonomic information to identify fishes.

The job of the Fish Taxonomist is to name and classify species in a way that makes it easier for fisheries scientists, and other “users”, to correctly identify fish species during their work.

Fish Taxonomy

All fishes (and other animals and plants) are therefore given unique names.

These names are divided into two components derived from the classical old European languages Latin or Greek.

The first part of a scientific name is called the generic name and the second is the species name.

Every fish, therefore, belongs first to a genus and second has its own unique species name. A genus is a group of very similar and closely related species.

The name of a person and year appearing after the species name refer to the name of the taxonomist who first officially described and named the species and the year of publication of the description (the comma between these is optional).

Conventionally, taxonomists are forbidden to change the species name once it has been published (unless it is accidentally the same as a prior existing name).

However, species names can be declared invalid in cases where the species is later considered to be the same as another previously described species.

In cases where taxonomists are unsure whether a fish is different enough from others to warrant it being called a different species they can declare (name) it a subspecies or variety of an existing species.

By convention the species name (i.e., genus + species) is always written in italics, with an initial upper-case letter for the genus and all lower case letters for the species name, to signify it is the recognized scientific name.

The family, order, class etc. should never be in italics.

With animal names the author name is always followed by a year; with plants, the author name or abbreviation is given alone.

Animals:Emydura signata Ahl, 1932

Macrotis lagotis (Reid, 1937)

(the bracket indicates that Reid ascribed the species to a different genus)

Plants:Melaleuca nervosa (Lindley) Cheel

synonym: Callistemon nervosus Lindley

(Lindley originally described it as a Callistemon; Cheel later transferred it to the genus Melaleuca).

What are the Tools of Taxonomy?

The taxonomist uses several characteristics or identification parameters. These can be divided into four main groups:

1.Parameters that can be measured: eg. standard length, snout length, fin length, and eye diameter.

Because fish differ in size these parameters are often expressed in relation to each other.

For example, the head length of a species may be stated as a percentage of its body length (as part of a description of its overall shape).

2. Anatomical parts that can be counted: eg. vertebrae, fin-rays, spines, teeth and scales. The absence of any of these from the fish can be

equally as important.

2. The appearance and position of body structures: e.g. the lateral line, teeth and scales and the coloration (of live fish).

3. Chromosome numbers and genetic parameters such as DNA sequences (requiring sophisticated measuring techniques).

Important anatomical terms used in fish taxonomy and identification and how they are used:

Important anatomical terms used in fish taxonomy and identification and how they are used:1. Mouth: Size and position of mouth. Mouth

protrusible or not protrusible. Mouth with teeth or without teeth, position of teeth in the mouth.

2. Teeth: Number, size, shape and kind of teeth.

3. Barbels: Number of barbels, their size and position.

4. Snout: Snout length.

5. Operculum: Operculum present or not, with or without spine(s).

6. Eye: Eye diameter, eye color in fresh specimens, position of eyes. Distance between eyes (interorbital space) in relation to eye diameter or snout length.

7. Head: Head shape. Head length in relation to standard length, eye diameter or barbel length

8. Predorsal scales: Number of scales from head to dorsal fin.

9. Dorsal fin: Number of dorsal fins, length of the fin(s), number of fin rays, with or without spine(s).

10. Pelvic fins: Position in relation to dorsal and pectoral fins, number of fin rays, united or not united into a disc.

11. Pectoral fins: Present or absent, with or without spines, position in relation to pelvic fins, length of the fins.

12. Anal fin: Length of the fin, number of fin rays.

13. Caudal fin: Present or absent. Caudal fin separate or continuous with dorsal and anal fin.

14. Dorsal fin spines: Present or absent. Number of spines. Smooth or with serrations. If serrated number of serrations.

15. Adipose fin: Present or absent. Size of the fin.

16. Lateral line: Complete or incomplete. The number of lateral line scales.

17. Caudal peduncle: Number of scales around caudal peduncle.

18. Scales: Present or absent. Scale shape and type.