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Biology of Fish

Fish belong to the group Chordata

Includes around 52,000 species including fish, mammals, reptiles, etc.

Characteristics of ChordatesChordates: named for the notochord structure

found in all chordate embryos. ◦Notochord: flexible rod that extends through the

length of the body

Diversity of FishFish were the 1st jawed vertebratesMake up 30,000 of the +52,000 species

of vertebratesTwo main groups of fish:

1. Cartilaginous fish: skeleton made of cartilage

• Ex. sharks and rays• One class: Chondrichthyes

2. Bony fish: skeletons contain bone hardened by calcium compounds

Ex. ray finned fish, coelacanths, and lungfish Three classes: Actinopterygii, Actinistia, Dipnoi

Chondricthyes (Sharks, rays, and ratfishes)• 850 species• Bony skeleton replaced with

flexible cartilage for buoyancy• no swim bladder• exposed gill slits• have well developed sensory

organs

Actinopterigii (ray-finned fish)• Flexible rays support fins• Operculum flap protects and ventilates gills• Air-filled swim bladder regulates buoyancy• Skin contains bony scales and lateral line pits• Most are oviparous (lay eggs) with external fertilization,

but many reproductive strategies can be found in this group including hermaphrodites capable of cloning themselves and species who give birth to live young

operculum

swim bladder lateral line

gills

Actinistia (lobe-finned fish)• Includes the coelacanth and tetrapod lineages • Thick muscles of pectoral and pelvic fins surround rod-

shaped bones

• Coelacanths were thought to be extinct until 1938 when they were discovered of the coast of east Africa. Since then a second population has been found in Indonesia

Dipnoi (Lungfish)

Found only in Southern Hemisphere

Adaptation to Air Sac that can function as lungs during periods of drought.

Also have gills to obtain oxygen from water.

What do fish need?Clean Water: Good pH, low ammonia, no harmful

chemicals

Oxygen: Take in oxygen dissolved in water

Food: Need high amount of protein

Proper Temperature: Fish are cold-blooded, so metabolism slows in cold temps

Proper Salinity: Depends on freshwater or saltwater

Fish AnatomyLateral line: sensory organs running along the

body help sense changes in water pressure (feel other animals)

Gills: extract oxygen from the surrounding waterSwim Bladder: aids in “hearing” for many fish

and transmits vibrations to sensory organs (sharks use electromagnetic fields), the lungfish use these as a respiratory organ to breath air

Fins: swimming and defense

Fish External Anatomy - Fins

Caudal fin - used for forward propulsion of the fish.

Soft dorsal fin - may be used for forward propulsion and as a rutter to change direction.

Spiny dorsal fin - used as a keel to maintain fish balance and stay upright. Can be lowered to increase streamlining of fish (increase swimming speed)

Pectoral fin - used for steering (braking and turning) and may be used for forward propulsion.

Pelvic fin - prevents fish from floating upward when fish brakes (with pectoral fins)

Anal fin - acts as a rudder for balance when turning, may be used for forward propulsion.

Fish External Anatomy - Fins

Fish Internal Anatomy

The digestive system is similar to other animals.

Size and shape of each component of the system will vary with the type of fish and its diet.

Carnivores◦Fish that eats meat.◦Have a large stomach and short intestines.

What are the parts of the fish digestive system?

Parts include:◦Mouth Teeth Tongue Branchiospines

◦Esophagus◦Stomach◦ Intestines◦Anus

What are the parts of the fish digestive system?

Mouth◦Entry point of system.

Carnivores mouth◦Have many teeth that point

inwards.◦Not used for chewing.◦Used to capture and hold prey.

Other fish◦Few or no teeth.

What are the parts of the fish digestive system?

Tongue◦Helps move food around in the

mouth.Branchiospines◦Act as filters to capture small food

from water as the fish swims.◦Part of the gill structure that

helps fish swim.Esophagus◦Short tube that connects mouth

to stomach.

What are the parts of the fish digestive system?

Stomach◦Organ where digestion begins.◦Some stomachs will expand greatly. Allows them to eat large quantities of

food.◦Other stomachs are small that will

accommodate small amounts of food.◦Some fish have almost no stomach. Esophagus connects directly to

intestines.

What are the parts of the fish digestive system?

Intestines◦Site of food digestion and nutrient absorption.

Anus◦Exterior opening of system.◦Unused food and wasted material is exited.

What are the parts of the fish digestive system?

Nervous System Relatively simple system Central Nervous System◦ Brain and Spinal Cord

Peripheral Nervous System◦ Cranial Nerves and Spinal Nerves

Muscular SystemMuscle segments in the shape of “W”Muscle is the edible part of the fish

Nervous/Muscular System

Heart and Blood Vessels2 chambered heart: distributes O2 in the body ◦ Atria-collects blood from body◦ Ventricle-sends blood to the gills◦ Humans have a 4 chambered heart – fish need less 02

Circulatory/Respiratory System

• Arteries: carry blood away from the heart• Veins carry blood back to the heartGills• Blood-filled membranes that exchange oxygen and carbon dioxide• Like the lungs in a human

EXIT SLIPWrite Name and Date on Top of half sheet1. What is one difference between

Cartilaginous Fish and Bony Fish?2. What are the three groups of Bony Fish?3. How does a fish’s heart differ from

humans?4. What type of Bony fish is a Tilapia?5. What organ allows a fish to stay

motionless in the water without sinking?