fish

ectothermic

ectothermic (cold-blooded) aquatic organisms with backbones

Jellyfish

A jellyfish - is a cnidarian - does not have a backbone - does not have gills

Lobsters

A lobster - is a crustacean - has an endoskeleton (an external protective layer) - has legs

Sea snakes

A sea snake - is a reptile - can come on land - does not have gills

A Cartilage Skeleton (cartilaginous fish)

A skeleton made of cartilage is the major trait that defines a fish as a cartilaginous fish. Cartilage skeletons are a result of not having the necessary gene to turn the cartilage into bone.

Whales

A whale - is a mammal - does not have gills - must come to the surface to breathe

What is an example of a ray-finned fish?

Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish)

Backbone

All fish have backbones. A backbone is a structure unique to all vertebrates that protects nerves that run along the dorsal (back) region.

Aquatic Lifestyle

All fish live in the water. Some may be able to come on land briefly, but even they must return to the water to survive.

External Fertilization

Although some reproduce through internal fertilization, the majority reproduce by external fertilization. These fish release gametes (sperm and egg cells) into the surrounding water, allowing them to combine.

Bilaterally Flattened

Bony fish are flattened on both the left and right sides, forming mirror images on their two sides. Most cartilaginous fish are flattened on the bottom, creating two distinct sides - a flat white bottom, where the gills are, and a top with color, where the fins and eyes are.

3-5 Pairs of Gill Slits

Bony fishes typically have 3-5 gill slits (for breathing) that are protected by an operculum. An operculum is a protective flap of skin.

Absence of Swim Bladders (cartilaginous fish)

Cartilaginous fish do not have swim bladders. The swim bladder is an internal gas-filled organ that helps a fish control buoyancy (the ability to float on water) by allowing the fish to take in more air, becoming lighter, or expelling air, becoming heavier. Some cartilaginous fish store large amounts of oil in their livers to help with buoyancy.

Internal Fertilization (cartilaginous fish)

Cartilaginous fish reproduce by internal fertilization. That is, the female's eggs are fertilized within the female body after sexual intercourse takes place. Many other fish reproduce through external fertilization, by releasing gametes (sex cells) into the water. This image shows fertilized eggs with offspring developing inside.

Sarcopterygii

Characteristics and examples of lobe-fin fish include: - fleshy fins attached to the body by a single bone - two dorsal fins - the coelacanth (shown) and the lungfish

Actinopterygii

Characteristics and examples of ray-fin fish include: - fins that have skin stretched over several spines - a single dorsal fin - sunfish, salmon, and pufferfish

What type of fish are chimaeras most closely related to?

Chimaeras are most closely related to sharks.

Presence of Dermal Denticles (cartilaginous fish)

Dermal denticles, which are tooth-like scales, cover the skin of cartilaginous fish. Other fish have flat scales, making them different.

Gills

Fish breathe using gills. Oxygen is absorbed from water through gills.

Vocal Cords

Fish do not have the ability to produce sounds with vocal cords, because they do not have vocal cords. Fish do produce sounds through other methods, though.

Name the traits that help define fish.

Fish have gills, are mostly ectothermic, don't have vocal cords, are aquatic, and have backbones.

What does it mean to be cartilaginous?

It means that the skeleton is made up of cartilage rather than bone.

Jawed Fish

Jawed fish came about shortly after jawless fish. They evolved around 430 million years ago and included a group known as the placoderms. Placoderms were jawed fishes with armored scales. An example of an early placoderm, Bothriolepis candensis, is shown here as a fossil. They fossilized easily because their armored scales were very hard and dense. Jawed fish were the first organisms to evolve jaws. What advantage did having a jaw provide to these fish? Having a jaw allowed these fish to prey upon more types of organisms. In effect, a jaw gave these fish a weapon to use on prey.

Jawless Fish

Jawless fish were the first fish to evolve. They were also the first vertebrates. None of them had jaws and all fed by filtering the water around them. They evolved nearly 530 million years ago. An example of a jawless fish is the lamprey, shown here.

What is one reason why a jellyfish is not a fish?

Jellyfish do not have backbones or gills, which are required characteristics of fish.

Lobe-fin Fish

Lobe-fin fish have fins that are fleshy and extend from the body on a single stalk (not several spines or bones). They evolved close to 419 million years ago. The lungfish, shown here, is a present-day example.

How many dorsal fins do lobe-fin fish and ray-fin fish have?

Lobe-fin fish have two dorsal fins, while ray-fin fish only have one.

What is an example of a lobe-finned fish?

Lobe-fin fish included the coelacanth and the lungfish.

Presence of Spiracles (cartilaginous fish)

Many cartilaginous fish have spiracles. Spiracles are positioned on top of the heads of all rays and skates and some sharks. They allow the fish to breathe while resting on the ocean bottom, when their gills may be blocked.

Mostly Ectothermic

Most fish are cold blooded. They rely on external sources to regulate their body temperature. Some fish are endothermic (create their own body heat), but the majority are not.

What is one type of cartilaginous fish?

One type of cartilaginous fish is a shark. Other types include rays, skates, and chimaeras.

Ray-fin Fish

Ray-fin fish are called this because their fins are webs of skin stretched over bony spines, as opposed to fleshy, lobed fins. Ray-fin fish comprise nearly 99 percent of all fish alive today. Ray-fin fish evolved just over 359 million years. The ocean sunfish shown is an example that swims the oceans today.

How are ray-fin and lobe-fin fish different?

Ray-fin fish have fins with skin stretched over several spines, while lobe-fin fish have fleshy fins joined to the body by a single bone.

How are rays and skates different?

Rays give birth to live offspring, and skates lay eggs.

Rays

Rays have flattened bodies and gills on their ventral (bottom) side. Rays, like skates, are related to sharks and evolved around 150 million years ago. The major difference between rays and skates is that rays give birth to live offspring (they do not lay eggs).

Smooth Scales

Scales in bony fish tend to be smooth and overlapping. Conversely, most cartilaginous fish have spiny scales.

Sharks

Sharks are aquatic fish with tooth-like scales and cartilaginous skeletons. The earliest known sharks evolved more 420 million years ago, but modern day sharks (like this great white shark) evolved around 35 million years ago. This group also contains the largest fish in the world--the whale shark.

Which group of cartilaginous fish contains the largest fish in the world?

Sharks contain the largest fish in the world, the whale shark.

If rays, skates, and chimaeras are all most closely related to sharks, what does it mean about the age of sharks?

Since rays, skates, and chimaeras are most closely related to sharks, they must have all evolved from early shark species. Sharks must have evolved before rays, skates, and chimaeras did. This means that sharks are some of the oldest cartilaginous fish on earth.

Skates

Skates are very similar to rays, having a similar body shape, evolving around the same time, and being related to sharks. The major difference between skates and rays is that rays give birth to live offspring, while skates lay eggs.

What are the two classes of bony fish?

Some common ray-fin fish are the salmon, the sunfish, and the pufferfish.

Spiny Sharks

Spiny sharks were a group of fish superficially similar to sharks of today, but differing in several ways, including having tiny scales covering their skin. They resembled small sharks and shared features of a couple different types of fish. Spiny sharks evolved close to 420 million years ago, but went extinct nearly 250 million years ago. Here, you can see several illustrated examples of extinct spiny sharks:(from top down) Mesacanthus pusillus, Parexus falcatus, and Ishnacanthus gracilis.

Chimaeras

The chimaeras' closest living relatives are sharks, even though they branched off from them nearly 400 million years ago. Chimaeras live in water depths deeper than 200 meters, have smooth skin, and have a venomous spine in front of their dorsal (top, back) fin.

Swim Bladder

The majority of bony fish have swim bladders. Swim bladders are organs that can be filled with air to balance buoyancy.

Bones

The skeletons of bony fish are composed of bones that protect internal organs and nerves. In cartilaginous fish, the skeletons are composed of cartilage.

Why have some of the first fish to evolve--jawless fish and lobe-fin fish--survived and still exist today?

These fish have lasted so long because they have very beneficial adaptations that have helped them to survive the changing world. Their body structures and feeding habits have kept them successful while competing with new organisms in the oceans.

bony vertebrates

vertebrates with skeletons composed of bone