Description Of Fish

Introduction

Identification of fish is an important aspect of the hobby.
This is series of 2 articles.
The first article describes the various body parts,
Body Parts of Fish , which can be used to identify the fish.
This second part of the article describes the process by which these body parts are used to describe the fish.

A fish is described by :

• Description of shape of various body parts.
• Description of measurements of various body parts also called Morphometric characters.
• Description of counts of various parts of body also called Meristic characters.

Morphometric characters

Many measurements are used to describe a fish, they are mostly represented as precentage((%) of either Standard Length or Total Length.

Some of the common terms used are:

Standard length

Standard length is the straight-line measurement taken from tip of snout to the last vertebra which supports the tail fin of the fish

Standard Length of a Fish
Image Credit: Sandeep Raghuvanshi

Total Length

Total Length is straight-line measurement taken from tip of snout to the end of caudal (tail) fin.

Total Length of a Fish
Image Credit: Sandeep Raghuvanshi

Fork length

Fork Length of a fish measured from the tip of the snout to the posterior end of the middle caudal(tail) rays.
This measurement is used in fish where it is difficult to ascertain the end of vertebral column.

Fork Length of a Fish
Image Credit: Sandeep Raghuvanshi

Pre-orbital length

The straight-line measurement taken from front of snout to anterior of eye.

Pre orbital Length of a Fish
Image Credit: Sandeep Raghuvanshi

Pre-pectoral length

The straight-line measurement taken from front of snout to origin of pectoral fin.

Pre Pectoral Length of a Fish
Image Credit: Sandeep Raghuvanshi

Head Length

The straight-line measurement taken from front of snout to the back of operculum(bony gill cover).

Head Length of a Fish
Image Credit: Sandeep Raghuvanshi

Pre-pelvic Length

The straight-line measurement taken from front of snout to insertion point of pelvic fin.

Pre Pelvic Length of a Fish
Image Credit: Sandeep Raghuvanshi

Pre-anal length :- The straight-line measurement taken from tip of snout to posterior edge of the anus. Body depth :- The vertical distance from the dorsal (upper) margin of the body to the ventral(lower) margin of the body measured at the base of the pectoral fin where it attaches to the body. Fins or fin bases are not included in the measurement. Caudal peduncle length :- The straight-line measurement taken from insertion of the anal fin and the caudal flexure. Pre dorsal length :- The straight-line measurement taken from front of snout to the insertion of first ray of dorsal fin. Eye- diameter :- Diameter of eye. Interorbital :- The space between the eyes, on top of the head; bones on the roof of the skull between the eyes. Nape :- The part of the back that extends from the margin of the skull to the dorsal-fin origin; also, the region of the head above and behind the eyes.

Fins

Meristic characters :- An accurate count of various body parts of fish form a important way to differentiate between various various species. Some of counts used are, counts of fin rays, scales, serration, teeth, color bands. Some of these are discussed below:- Ray Counts:- As already discussed in part 1 , fins are made of thin mobile filaments attached to body of fish and are covered with thin membranes. Conventional abbreviations for the various fins in the reporting of numbers of fin rays are: D-dorsal A-anal C-caudal p-pectoral P 2- pelvic There are two basic types of fin rays, true spines and soft rays. Spines:- Spines are single, median structures that are un branched and lack joints. Spines normally occur in the anterior part of a single fin or in the anterior of two separate fins. All true spines (simple, un branched, un segmented fin rays) are designated by upper Roman numerals whether they are stiff or flexible.(I, II, III, IV...) Rays:- Rays comprise two longitudinal supports, jointed and typically branched. Soft rays which are simple( not branched) are designated by lower case roman numerals (i,ii,iii,iv...) Soft rays which are branched are designated by Arabic numerals (1,2,3,4). Direction of Count :- Dorsal Fin rays are counted back to front, .i.e the posterior most ray is counted as first ray and count is done towards anterior (front). Anal Fin rays are counted front to back just reverse of dorsal fin rays. The anterior most ray is counted as first ray and count is done towards posterior. Caudal(tail) Fin rays are counted from outermost to inner most ray. Scales:- Nearly all bony fish (Osteichthyes) have scales except catfish. These may be cycloid, ctenoid. They may be embedded in pockets in the skin and may be easily shed or firmly attached. Some important counts are Lateral Line Scale Count :- This count is the number of scales with perforations along the lateral line up to the caudal(tail) base. The scales wholly on the tail fin base or beyond this point are excluded. If the lateral line is divided like in case of Cichlids, then all scales on both portions are counted. However in case of lower line the first scale is the scale which is directly below the last scale on upper line. They are referred to as L.L and L.I in fin formula. Scale Count From Dorsal Fin to Lateral Line :- This count is made from the insertion of the first dorsal fin downwards and backwards following the natural scale row to the lateral line. The scales on the lateral line itself are excluded. Scale Count from Lateral line to Pelvic fin base :- This count is made from the insertion of the pelvic fin base to the lateral line. The scales are counted upward and forward. The scales on the lateral line itself are excluded. Pre-Dorsal Scale Count :- This count is made from the origin of the first dorsal to the last scale on the head. It is indicated by P.D.S in fin formula. Pre-Anal Scale Count :- This count is made from the anterior most origin of anal fin to the last scale on the head. Circumpeduncular Scales :- They are counted around the least depth of the caudal peduncle. Gill rakers :- Gill rakers are thin filament like structures on gill arches. For count purposes the rakers on first gill arch are taken. Pharyngeal teeth :- Pharyngeal or throat teeth are found in fish like cichlids and Cyprinids. In these fish the fifth gill arch is modified and each has either 2-3 rows of teeth. The teeth in each row are counted and indicated from left to right. The teeth formula 3,5 -4,3 will mean that there are 3 teeth on the left side in the outer row and five in the inner. The right side has 4 teeth on the outer row and 3 in the inner row.