VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

NORMAL ANATOMY OF FINFISH

 

FINS AND THEIR FUNCTIONS

Fins of fishes are made up of stiff rays covered by skin. Some may be jointed and some separate near the edge of the fin. In certain fishes, some of the rays supporting the fin are bony, stiff and unjointed. They are referred to as spines. The number of rays in the fin is also used in classification.

Type of fin	Functions
Dorsal fin	Stability in swimming.
Ventral fin	Helps to provide stability in swimming
Caudal fin	Helps in propulsion
Anal fin	Stability in swimming
Pectoral fins	Locomotion and side to side movement
Adipose fin	Stability in swimming

SKIN AND SCALES

 

Skin

• The skin of fish is divided into two layers, the epidermis (outer) layer and the dermis. The epidermis is made up of epithelial cells, arranged one above the other. These cells are constantly shed and replaced with new ones. The dermis lies under the epidermis

Scales

• The deeper place drmis of the skin is made up of connective fbroblasts, collagen and blood vessels. The scales of a fish lie in pockets in the dermis and come out of the connective tissue. The scales overlap and so form a protective flexible armour capable of withstanding blows and bumping.

Type of scale	Description
Placoid	Placoid scales are made of dentin covered by enamel. Present in sharks and rays.
Ganoid	Ganoid scales are flat, basal-looking, seen on the skin with little overlapping. Present in gar fish
Cycloid	Small oval-shaped scales with growth rings. Present in carps
Ctenoid	Look like cycloid scales but have spines covering one edge. Cichlids possess this type of scales

Cycloid scales	Ganoid scales	Placoid scale	Ctenoid scale

GILLS AND LATERAL LINE

Gills

• Gills help in the respiration. It is located under the gill covers. The walls of the pharynx is perforated by five slit-like openings. The tissue between the slits is called the gill arch. On each side of the fish there are five gill slits and four gill arches. On the gill arches are mounted the actual gills, a delicate system of blood vessels covered by a very thin epithelium through which the gaseous exchange takes place.

Lateral line

• The lateral line consists of a series of scales, each modified by a pore, which connects with a system of canals containing sensory cells and nerve fibers. It runs in a semi line from the gills to the tail fin. It can be easily seen in fish as a band of darker looking scales running along the side. The lateral line has shown to be a very important sensory organ in fish. It can detect minute electrical currents in water. It can also function as a kind of echo location process that helps the fish identify its surroundings.