Chordates and Fish

–Members of the phylum Chordata are called chordates.

• a dorsal, hollow nerve cord

• a notochord

• pharyngeal pouches

• tail that extends beyond the anus.

​–A chordate is an animal that has, for at least some stage of its life:

​The Hollow nerve cord is a bundle of long strands of nerves that eventually develops into the spinal cord.

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•The notochord is a long supporting rod that runs through the body just below the nerve cord. This eventuall becomes the vertebrae in vertebrate animals.

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•Pharyngeal pouches are paired structures in the throat (pharynx) region.

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• ​Later in development they become:

  • Lungs in mammals, reptiles, and amphibians

  • Gills in bony fish and sharks

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•The tail can contains bone and muscle and is used for swimming by many aquatic species.

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• About 96 percent of all chordate species are vertebrates.

• Most vertebrates have a vertebral column, or backbone.

• In vertebrates, the dorsal, hollow nerve cord is called the spinal cord.

  • As a vertebrate embryo develops, the front end of the spinal cord grows into a brain.

• The notochord develops into the vertebrae​ (backbone)

  • The backbone is made of individual segments called vertebrae.

  • In addition to support, vertebrae enclose and protect the spinal cord.

• The two groups of invertebrate chordates are: tunicates and lancelets.

  • Similarities in anatomy and embryological development indicate that vertebrates and nonvertebrate chordates evolved from a common ancestor.

  • Both tunicates and lancelets are soft-bodied marine organisms.

What are the basic characteristics of fishes?

• Fishes are aquatic vertebrates.

• Most fishes have paired fins, scales, and gills.

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What were the important developments during the evolution of fishes?

• Fishes and invertebrate chordates probably evolved from common invertebrate ancestors.

• Jaws and paired fins were important developments during the rise of fishes.

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​Evolution of Fishes

The First Fishes

• The earliest fishes to appear in the fossil record lived about 510 million years ago.

• These fishes were jawless and had bodies covered with bony plates.

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​Evolution of Fishes

The Arrival of Jaws and Paired Fins

• Jaws with muscles and teeth made it possible for fish to eat a wider variety of foods.

• Animals with jaws can also defend themselves by biting.

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​Evolution of Fishes

The Arrival of Jaws and Paired Fins​

• Fishes evolved paired pectoral (anterior) and pelvic (posterior) fins.

• These fins were attached to girdles—structures of cartilage or bone that support the fins.

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​Evolution of Fishes

 Cartilage -is a strong, dense connective tissue that supports the body and is softer and more flexible than bone.

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​Evolution of Fishes

The Arrival of Jaws and Paired Fins​

• Paired fins gave fishes more control of body movement.

• Tail fins and powerful muscles gave fishes greater thrust when swimming.

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​Evolution of Fishes

• Early jawed fish soon disappeared, but left behind two major groups that continued to evolve and still survive today.

  • One group

    • the ancestors of modern sharks and rays—evolved a skeleton made of strong, resilient cartilage.

  • The other group

    • evolved skeletons made of true bone.

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The Rise of Modern Fishes

How are fishes adapted to life in water?

• Adaptations to aquatic life include:

  • various modes of feeding,

  • specialized structures for gas exchange,

  • and paired fins for locomotion.

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Form and Function in Fishes

​Feeding

• Every mode of feeding is seen in fishes.

  • herbivore, carnivore, detritovore, filter feeding,​ etc.

• A single fish may exhibit several modes of feeding, depending on the type of food available.

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Form and Function in Fishes

•Food passes through the mouth and esophagus, into the stomach.

•In the stomach, the food is partially broken down.

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Digestive system

• food is further processed in fingerlike pouches called pyloric ceca.

•The pyloric ceca secretes digestive enzymes and absorbs nutrients from the digested food.

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Digestive system

• The liver adds bile to help break down fats

• The pancreas the adds insulin to help break down sugars

• They both add other digestive chemicals to the food as it moves through the digestive tract.

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Digestive system

• The intestine completes the process of digestion and nutrient absorption.

• Undigested material is eliminated through the anus in the form of feces.

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Digestive system

•Most fishes exchange gases using gills located on either side of the pharynx.

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Respiratory system

• ​Fishes use their gills to exchange gases by pulling oxygen-rich water in through their mouths,

• pumping it over their gill filaments,

• and pushing oxygen-poor water out through openings in the sides of the pharynx.

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Respiratory system

Respiratory system

• Fishes have a

  • closed circulatory systems

  • a two chambered heart

  • that pumps blood around the body in a single loop

    • from the heart to the gills,

    • from the gills to the rest of the body,

    • and then back to the heart.

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Circulatory system

• ​In most fishes, the heart has four parts:

  • the sinus venosus

  • the atrium (first chamber)

  • the ventricle (second chamber)

  • the bulbus arteriosis

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Circulatory system

• Oxygen-poor blood from the veins collects in the sinus venosus, ​from the sinus venosus blood travels to the atrium.

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• The atrium is a large muscular chamber that serves as a one-way compartment for blood that is about to enter the ventricle.

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• Blood enters the atrium and flows to the ventricle.

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• The, ventricle is a thick-walled muscular chamber that is the actual pumping portion of the heart.

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• The ventricle pumps blood into the bulbus arteriosus.

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• The bulbus arteriosus moves blood into the ventral aorta and toward the gills.

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• ​Fishes eliminate nitrogenous wastes in the form of ammonia.

• Some wastes diffuse through the gills into the surrounding water.

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Excretory system

• ​​Others wastes are removed by kidneys.

  • The kidneys of marine fishes concentrate wastes and return water to the body.

  • The kidneys of freshwater fishes pump out dilute urine.

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Excretory system​

Fishes have well-developed nervous systems organized around a brain.

• ​The olfactory bulbs are involved with the sense of smell, or olfaction.

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Nervous System

• In most vertebrates, the cerebrum is responsible for all the voluntary activities of the body.

• In fishes, however, the cerebrum primarily processes the sense of smell.

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• The optic lobes process information from the eyes.

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• The cerebellum coordinates body movements.

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• The medulla oblongata controls the functioning of many internal organs.

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• Almost all fishes that are active in daylight have well-developed eyes and color vision.

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• Many fishes have extraordinary senses of taste and smell.

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• ​Most fishes have ears but may not hear sounds well.

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Nervous system​

• Fishes use the lateral line system to sense the motion and vibrations of other fishes or prey swimming nearby.

• Some fishes can detect low levels of electric current.

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Nervous system​

• Many bony fishes have an internal, gas-filled organ called a swim bladder that adjusts their buoyancy.

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Nervous system​

• Most fishes move by contracting paired sets of muscles on either side of the backbone.

• A series of S-shaped curves move down the fish’s body.

• The force and the action of the caudal fins propels the fish forward.

• The pelvic, pectoral, and anal fins of fishes are used to keep on course and adjust direction.

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Movement​

Movement​

• The eggs of fishes are fertilized either externally or internally, depending on the species.

• Fish can be oviparous or ovoviviparous.

  • ovi (ovo) - egg

  • vivi - live birth

  • parous - to produce young by ​

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Reproduction​

• In oviparous species the embryos develop inside of the eggs and hatch outside the mother's body  

  • The young are laid as eggs

  • The embryos obtain food from the yolk in the egg.

  • The babies hatch from the eggs

    • oviparous species include: most insects, fish, amphibians, reptiles & birds

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Reproduction​

• In ovoviviparous species, the eggs stay in the mother's body after internal fertilization.

  • Each embryo develops inside its egg, using the yolk for nourishment, no umbilical connection

    • The young are “born alive”. (some sharks, reptiles)

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Reproduction​

• In viviparous animals, the embryos stay in the mother's body after internal fertilization.

  • These embryos obtain the substances they need from the mother's body (not from material in an egg).

  • The young of viviparous species are “born alive.”

    • Viviparous animals include: (Placental mammals: Humans, elephants, lion, dogs etc.)

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Reproduction​

• All living fishes can be classified into three groups:

  • Agnatha (a-no, Gnatha –Jaw) - jawless fishes,

  • Chondrichthyes: (Chondro- cartilage, ichtyes – fish) cartilaginous fishes

  • Osteichthyes: (oseto- bone, icthyes – fish) bony fishes.

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Groups of Fishes ​

Class: Agnatha - Jawless Fishes

• Jawless fishes have no true teeth or jaws.

• Their skeletons are made of fibers and cartilage.

• They lack vertebrae, and keep their notochords as adults.

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Groups of Fishes ​

Class: Agnatha - Jawless Fishes​

• Modern jawless fishes are divided into two families:

• Petromyzontida: (Petro- stone, myzontida – sucking) lampreys

• Myxini: (myxa-slime) hagfishes.

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Groups of Fishes ​

​Class Chondrichthyes - cartilaginous fish

• contains sharks, rays, skates, sawfishes, and chimaeras.

• The skeletons of these fishes are built entirely of cartilage.

• Many sharks have thousands of teeth arranged in several rows.

• Most species of sharks do not attack people.

Groups of Fishes ​

​Class Chondrichthyes - cartilaginous fish​

• Some skates and rays feed on bottom-dwelling invertebrates.

• The largest rays eat floating plankton.

• Skates and rays glide through the sea with their large, wing like pectoral fins.

• Many skates and rays cover themselves with sand and rest on the ocean floor.

Groups of Fishes ​

Class Osteichthyes - Bony fishes

• Their skeletons are made of bone.

• Almost all living bony fishes are ray-finned fishes.

• “Ray-finned” refers to the slender bony spines, or rays, that are connected by a thin layer of skin to form the fins.

Groups of Fishes ​

Class Osteichthyes - Bony fishes​

• Only seven living species of bony fishes are not classified as ray-finned fishes.

• These are the lobe-finned fishes, a subclass that includes lungfishes and the coelacanth.

• The fleshy fins of lobe-finned fishes have support bones.

• Some of these bones are jointed.

Groups of Fishes ​

• ​Most fish have to remain in either fresh or saltwater for their entire lives – they cannot tolerate the other type of water

  • Some fishes spend most of their lives in the ocean but migrate to fresh water to breed. These fish are called anadromous.

    • EX: Salmon

Ecology of Fishes ​

• ​Most fish have to remain in either fresh or saltwater for their entire lives – they cannot tolerate the other type of water

  • Some fish spend most of the lives in fresh water but migrate to the ocean to breed.  These fish are called catadromous.

    • EX: European eels

Ecology of Fishes ​