CLASSIFICATION OF FISH OR AQUATIC ANIMALS

CLASSIFICATION

A system of classification provides the means for resolving the problem of the origin and evolution of life. Classification involves scientific philosophy that uses inductive procedures.

Primary function of classification is to create order out of chaos by leading to accurate identification of individuals and to their ranking or arrangement into various taxa since it is impossible to discuss or think about organisms. The modern systematist utilizes information from a great variety of disciplines – genetics, ecology, paleontology, comparative physiology, animal behavior, cytology, zoogeography, biochemistry, biometrics and related fields. Background information from such discipline is essential for the solution of many taxonomic problems. Systematics has become the focal point of many fields of biology since it deals with organic diversity, a major integral branch of biology.

To know the correct name of a fish is of great importance if one is to take advantage of the work already done by others and thus save a lot of unnecessary expense and effort. Only the use of the scientific names of fish will permit this, they are the same in all languages, whether Japanese, Arabic or English.

Any group of fish, or of any other animal for that members are similar in structure and appearance and are capable of breeding among themselves, are said to belong to the same specie. The singular is usually abbreviated sp. and the plural spp. If specimens form a certain locality show minor differences from others found elsewhere, they are refereed to as a sub- species or variety.

A group of species which  closely resemble one another in  structure but which  do  not interbreed, are said to constitute a genus (plural genera). For the correct name of a fish, both the generic and specific names must be given, and sub-specific or variety names are added if they exits. The generic name should always begin with a capital letter and the others with lower case letters. The names are usually printed in Italics, or in typing they are underlined.

Despise this, confusion sometimes arises as a result of different authors mistakenly using different names for the same species. Thus it is customary in more detailed work to add the name of the person who first described the species, and sometimes also the date that his description was first published. Thus “ Clarotes macrocephalus Daget 1954” indicates that this species was first described by Daget in his publication of that year and such name should be used only for the species intended by the author. Bracket around the author’s name

indicates that, although the original description is still accepted as correct, for some technical reason the name fist given by the author is no longer valid and has been changed. Thus” Hepsetus odoe (Bloch)’ means that this species, first described by Bloch as Sarcodaces odoe, was in fact a member of the genus Hepsetus.

Genera in turn fall into larger groups known as families, and these into sub-order and so on. But for general fisheries work it is sufficient to trace the fish back only as far as its family.

When writing about fish it is customary to put the families into ascending order, according to their place in the evolutionary ladder. This is determined on the basis of knowledge gained from studying fossil and the degree of advancement of structure in modern fish. Thus Protopterus and Polypterrus, belonging as they do to separate sub- classes which evolved long  before other  fishes, take precedence over  Pellonula (a clupeid), or the slightly more advanced osteoglossid, heterotis, and so on until one comes to the Cichilds and Cyprinodonts which are reckoned to be more recently evolved and advance in structure.

To track down the correct name of a fish by examining their visible eternal features, but this is not always so and exact identification sometimes requires a detailed examination of such parts as gill rakers, air-bladder or the skeleton.

REASONS FOR CLASSIFICATION

1. To create order out of confusion by making accurate identification of every
2. To serve as guide on relationship between
3. To identify the differences out of different Since the categories in classification are based on the degree of similarities so that the more closely related organism or group of organism are, the more on factors or characteristics they shared together.
4. Because of varying shapes, sizes, physical and physiological diversities fishes possess, there is reason that fishes must be classified and

MEHODS OF STUDYING TAXONOMY OF FISHES

1. MERISTIC CHARACTERS: there are feature on fish which can be counted g. spines and rays of a particular fin. In many fish, some of the rays, especially of the dorsal fin, are replaced by strong and sharp spines; these are counted separately when describing a fish. Roman numerals are customarily used for spine counts. In Tilapia zilli, DXIV- XVI, 11-13; A111, 7-10, are fin counts. These indicate that T .zilli has from 14-16 spines and 11-13 rays on the dorsal fin; 3 spines and 7-10 rays on the anal fin.
2. MORPHOMETRIC CHARACTERS: They are characters that represent the They are always measurable characters e.g body depth, fork length, standard length, total length, front length etc. In using these morphometric characters for identification, the ratio of these lengths are used which are peculiar to a certain species within a certain range. E.g. BD      0.4 –0.6 TL There is disadvantage in using the total length (TL) because caudal fins may be damage before measuring it. Hence, it may give inaccurate measurement and may even be difficult to measure.
3. ELECTROPHORETIC METHOD: This involves the analysis of component proteins in the blood or tissue in identifying A jot of the fish blood or extract from the ground muscle is taken and chromatographed. In the process, component protein in the extract travel at different velocity hence separated apart. The distance at which the proteins are after settlement to each other is relevant and peculiar to that specie of fish.

Racial study: it involves separation into different racial stocks. This is only relevant to a particular species of fish. The third name of a fish reflects its race. The past for this study is the salinity and temperature which affect the features seen in fishes even though they are the same specie.

METHODS OF CLASSFICATION

Generally, seven standard categories forms the internationally accepted groups of classification for all living organisms. These standard categories are:

1. Kingdom
2. Phylum (phyla)
3. Class
4. Order
5. Family
6. Genus ( Genera)
7. Species (species)

 

 

The complexity and diversity increase downward; from kingdom to specie. Therefore, we find fish names existing in the genera and species levels. In a attempt to make the classification table more meaningful and to give room for major dissimilarities we have within the seven major divisions sub-divisions e.g. sub- phylum, super class, sub order etc. and of recent, varieties have just being recognized in the taxonomic hierarchy just after specie level.

RULE OF CLASSFICATION

1. Internationally, consensus has been reached that in biological classification Latin scientific names should be used any where in the Reason being that vernacular names tend to be different even within thesame locality.
2. In genera, generic name must always begin with capital letter while the specific name must begin with small E.g. Lates niloticus note “L” and “n” the generic  and  specific  name  must always  be underlined g. Clarias gariepinus, Oreoochrosiis niloticus or italiased
3. The followings have been internationally agreed upon is ending for their corresponding

The naming system comprising of specific and generic name is called BINOMIAL SYSTEM OF CLASSIFICATION.

CHARACTERTISTICS OF CHORDATES

1. The presence of notochord which runs longitudinally, from the anterior to the posterior end of the
2. The possession of a nerve cord which is dorsally oriented except in the primitive
3. The possession of holes in the pharynge (throat) called silts or

CHARACTERTISTICS OF VERTEBRATES

1. They possess some form of
2. They possess some trace of vertebral
3. The front end of the nervous system is differentiated into an elaborate brain, associated with special receptors like eyes, nose
4. The meter organisation of the body allows the performance of delicate movements to suit the situations that the receptors
5. Presence of heart, at least 3 chambers, assisting in circulation of
6. The presence of haemoglobin in the red corpuscles as an act of carrying oxygen in the
7. The excretory system consists of meso-dermal funnel (kidney) which functions as osmo-

CHARACTERISTICS OF ELASMOBRANCHII

1. They are
2. They possess 5-7 gill slits
3. They have
4. When scales are present, they are the placoid
5. They also have cloaca (unrinogenital) which has intermittent organ called

CHARACTERISTICS OF CHONDRICHTHYES

1. They possess constricted notochord
2. They all have jaws
3. The skeletons are cartilaginous
4. They have the paired and unpaired fins
5. Nostrils are in pairs
6. They have three semi-circular canals in the ear
7. The cranium is not totally fussed to the arch (not joined by connective tissues).
8. They possess placoid scales
9. Mouths are inferior

CHARACTERISTICS OF OSTEICHTHYES

1. They have bony jaws, skull and skeleton
2. Gills are usually 4 pairs, in number
3. They possess operculum
4. The scales are bony either cycloid ctenoid or ganoid
5. Most are oviparous (egg layers) with external fertilization and high fecundity
6. Most of them posses air bladder
7. Respiration is by pumping by buccal/opercular

TAXONOMIC HIERACHY

 

The external features of a scaleless fish.

1. Operculum Lateral line
2. Cephalo- muchal shield Pelvic fin
3. Dorsal spine
4. Pectoral spine
5. Dorsal filament
6. Pectoral fin
7. Dorsal fin
8. Humeral process
9. Adipose fin
10. Maxillary barbel
11. Caudal pedunle
12. Outer mandibular barbel
13. Caudal fin
14. Inner mandibular barbel
15. Anal fin

The external feature of a scaly fish.

1. Dorsal fin
2. Lateral line
3. Adipose fin
4. Pelvic fin
5. Dorsal spine
6. Pectorial fin
7. Caudal peduncle
8. Operculum
9. Anal fin