Category: Biology Second Paper

Fish scales that are round or oval, with growth lines and smooth edges are called cycloid scales. The inner part of the rib is called the anterior part, the outer part is called the posterior part and the two side parts are called the lateral parts. The tip has longitudinal grooves or radii. For example – Labeo rohita. Dr. Siddiq Publications

If two segments of the caudal fin of a fish are equal, it is called homocircular. Fishes of the class Actinoterygii have homocercles. For example – Ilisha (Tenualosa ilisha).

Those fishes that have barbs around their mouth like cat’s whiskers are called cat fish. Catfish belong to the class Actinopterygii. For example, horn fish, magur fish etc. Dr. Siddiq Publications

Ilisha- Tenualosa ilisha
Roe – Labeo rohita
Catla- Catla catla
Taki fish – Channa punctatus
Magur fish – Clarias batrachus
Boal- Wallago attu
Queen fish – Botia dario
Tuna fish – Thunnus albacares
Where fish- Anabas testudineus
Chital fish- Notopterus chitala
Pangasius fish – Pangasius pangasius
Cirrhinus cirrhosus
Bombay Dak/Lytra fish- Harpadon nehereus
Sturgeon fish – Acipenser oxyrhynchus
Paddle fish – Polyodon spathula
Horn fish – Heteropneustis fossilis
Sunfish – Mola mola

1. Their endoskeleton is made up of bones.
2. Body covered with cycloid, tinoid and ganoid scales. Some fish do not have scales. Such as- horn, Magur etc. Dr. Siddiq Publications
3. All body fins are bony and have dermal rays (lepidotrachea).
4. Their gills are covered with kanko.
5. Caudal fin homocircular type. That is, the tail fin is divided into two equal parts.
6. Their mouth is located at the tip.
7. Their brain consists of cerebellum, optic lobe and cerebrum.
8. There are 10 pairs of carotid nerves in the body.
9. The reproductive organs consist of four pairs of gills. On both sides of the head, there is a flower opening. Dr. Siddiq Publications
10. Air sacs are present in the body.
11. They breathe and float with the help of crackers.
12. Their heart is two-chambered and known as the venus heart.
13. They are unisexual animals. Excretion occurs. Direct and indirect effusion is observed.
[key words to remember features: endoskeleton, cycloid, tenoid, ganoid, cutaneous ray, conch, homocercal, pore, brain, carotid nerve, gill, air sac, heart]

The word Actinopterygii is formed from the Greek word actis meaning rays, pteryx meaning fin. Actinopterygii means ray-finned. Ray-finned fishes are known as Actinopterygii. About 96% of living fish belong to this category. They are 10 mm to 4 m long and weigh 1500 kg. Their number of species is 31,045. 12 classes, 48 tribes and 253 species of this class have been identified in the fresh water of Bangladesh.

The word Chondrichthyes is formed from the Greek word chondros meaning cartilage and ichthys meaning fish. Cartilaginous fishes belong to the class Chondrichthyes. They are marine and carnivorous animals. Their number of species is 1,207.

Characteristics of Chondrichthys
1. Their body is flat or mace-shaped. They are jawed animals.
2. Their endoskeleton is made of cartilage.
3. Their body skin is hard and tough.
4. Body covered by placoid scales.
5. There are 5-7 pairs of gill slits on both sides of the head.
6. They do not have horns.
7. The mouth and nostrils are located at the base of the digit. There are numerous rows of placoid teeth in the jaws. Siddiq Publications
8. The body does not have air sacs or sacs.
9. The digestive system consists of a J-shaped stomach, a spiral-shaped intestine, and a fatty liver.
10. Their heart is two-chambered and known as the venus heart.
11. Caudal fin heterocercal type. That is, the caudal fin is divided into two unequal parts.
12. In male fish the pelvic fins are modified to form copulatory organ clusters.
13. They are unisexual animals. Fertilization occurs. Direct exposure. They are ovaries, ovaries or uterus. Dr. Siddiq Publications

[KEY WORDS TO REMEMBER CHARACTERISTICS: flattened, cartilaginous, placoid, pharynx, concho, cracker, heterocercal, clasper]

Some animals of the Chondrichthyes
Shark- Scoliodon sorrakowah
Thutree shark- Scoliodon laticaudus
Hammerhead shark- Eusphyra blochii
Saw fish – Pristis pectinata
Ratfish- Hydrologus collei
Guitar fish – Rhinobatos rhinobatos
Raja – Raja raja
Sting Ray – Plesiobatis daviesi
Electric fish – Torpedo torpedo
White skates- Rostroraja alba
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Placoid scale
Microscopic scales present in the skin of cartilaginous fish are called placoid scales. It is a triangular plate formed from the skin. It has three sharp spines. For example – Scoliodon laticaudus. Dr. Siddiq Publications

Heterocercal
If the caudal fin segments of fish are not equal then it is called heterocercal. Chondrichthys fishes have heterocercles. For example, Scoliodon laticaudus.

Dog fish
The fish whose mouth is shaped like a dog’s mouth are called dog fish or dog fish. Their jaws have sharp teeth. Dogfish belong to the Chondrichthyes class. For example – Scoliodon laticaudus. Dr. Siddiq Publications

Sow fish
Those fishes which have a long tip like a saw at the front of their body are called saw fish or saw fish. They belong to the Chondrichthyes class. For example – Pristis pectinata.

Those fishes which have a long tip like a saw at the front of their body are called saw fish or saw fish. They belong to the Chondrichthyes class. For example – Pristis pectinata.

The fish whose mouth is shaped like a dog’s mouth are called dog fish or dog fish. Their jaws have sharp teeth. Dogfish belong to the Chondrichthyes class. For example – Scoliodon laticaudus. Dr. Siddiq Publications

If the caudal fin segments of fish are not equal then it is called heterocercal. Chondrichthys fishes have heterocercles. For example, Scoliodon laticaudus.