Characteristics of Bony Fish

The Osteichthyes are popularly called the bony fishes. They are the most successful of all aquatic forms. This is attested by the fact that they outnumber all other vertebrates combined together in the number of their species as well as in population.

The bony fishes show the following characters:

1. Body Form:

Body is usually spindle – shaped, being streamlined for active movement through water.


2. Appendages:

Both median and paired fins are present. These are supported by cartilaginous or bony fin rays (lepidotrichia) in the distal part. Pectoral fins do not act as elevators. Pelvic fins are more forwardly placed and lack claspers in both the sexes. Caudal fin is usually homocercal. There is generally a single dorsal fin.


3. Skin:

Skin has many mucous glands in the epidermis and usually contains dermal scales embedded in the dermis. The scales are ganoid, cycloid or ctenoid. Ganoid scales are diamond – shaped and have a covering of hard, enamel – like ganoin. Cycloid scales have smooth margin. Ctenoid scales have rough or spiny posterior margin.


4. Muscles:

Muscels of the trunk and tail are arranged in Z -shaped myomeres.

5. Endoskeleton:

Endoskeleton is partly or wholly bony. This represents a primitve condition. Vertebrae are numerous. Notochord often persists in a greatly reduced form. Pelvic girdle is often absent.


6. Coelom:

Coelom is divided by a septum transeversum into an anterior small
pericardial cavity that contains the heart and a posterior spacious
peritoneal cavity which has all other viscera in it. . B

7. Digestive System:

Mouth is usually terminal (anterior) and often bears numerous teeth. Jaws are well – developed and articulated to the skull (autostylic). Alimentary canal leads to the exterior by anus, there being no cloaca.


8. Respiratory System:

Respiratory system includes 4 pairs of gills. The gills are filamen­tous and are borne on bony gill arches. They are covered by oper­cular folds, which are supported by bony elements, spiracles are mostly lacking.

9. Air Bladder:

An air or swim bladder is often present. In some cases it leads by a duct to the pharynx.

10. Circulatory System :

Heart is 2 – chambered, having only one auricle and one ventricle. Sinus venosus and conus arteriosus are present. Heart contains only venous blood. There are 4 pairs of aortic arches. Red blood corpuscles are oval and nucleated.

11. Nervous System :

Brain has relatively small olfactory lobes and a small cerebellum. There are 10 pairs of cranial nerves.

12. Sense Organs:

Olfactory sacs are paired and dorsal. They communicate with the mouth cavity in lung fishes. Ear consists only of membranous labryinth, which bears 3 semicircular ducts. Lateral line organs are well – developed.

13. Endocrine Glands:

Endocrine glands almost confine to the general vertebrate plan.

14. Excretory System :

Kidneys are mesonephric. Waste matter is mainly ammonia.

15. Reproductive System in bony fishes:

Sexes are separate. Gonads are paired. Reproductive ducts lead directly to the exterior. Fertilization is generally external. Most forms are oviparous, some are ovoviviparous or even viviparous.

16. Development:

Eggs measure upto 12 mm. and contain variable amount of yolk, segmentation is usualy meroblastic. No embryonic membranes are formed. Larvae may differ greatly from the adults.

17. Body Temperature:

Body temperature is variable (poikilothermous).

18. Habit and Habitat of Bony fish:

Bony fishes occur in all sorts of water, fresh, brackish (saltish), warm and cold. They vary greatly in size Some are less than 10 mm. while sword fish may grow over 4m. Average size is 30 to 90 cm. There are about 30, 000 species of bony fishes.

Examples of Bony Fish: Exocoetus, Hippocampus, Echeneis cyanoglossus.



Evolution of Bony Fish

The bony fishes show advancement over the cartilaginous fishes in having a symmetrical or homocercal tail, an autostylic jaw sus­pension, a hydrostatic swim bladder, fili form gills capable of absorb­ing four-fifth of oxygen content of the respiratory water, and a better developed brain.





Bony fishes are beneficial to man in the following ways :

They provide products of commercial value. Fish oil, fish meal and liquid glue are important fish products.

i. Fish Oil: Liver of cods yields oil. This oil, in its crude form, is used in paints and insecticide sprays, and, in refined form, is taken as a source of vitamins A and D.

II. Fish Meal: Scraps from canneries and entire fishes of some species are dried and ground into a meal, which is used as an ingredient in the poultry feeds and as a fertilizer.

iii. Liquid Glue: Liquid glue is obtained from heads and trimmings of certain fishes.

Differences be­tween cartilage fishes and bony fishes.

Comparison of Cartilaginous fish and Bony Fishes





Mostly marine

Both fresh – water and marine.


placoid scales. Teeth are modified placoid scales

Scales are ganoid, cycloid or ctenoid.



Mostly, bony

Jaw suspen­sion, caudal fin, claspers

Hyostylic, heterocercal. claspers present to inject sperm into genital tracts of female

Mostly amphistylic homocercal or diphycercal. Claspers absent.


It is situated ventrally. It is subterminal

Mouth terminal


In majority, spiracles are found behind the eyes

Spiracles absent


In majority five pairs of gill- openings.

Gill openings covered by operculum are present.


Short, with spiral valve

Long, without spiral valve








Females lay large eggs or are viviparous i.e., give birth to young ones.

Females lay large and several eggs

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