Fishes Today, we will talk and learn about: Where fish fit in the Animal Kingdom. The different “classes” of fish. External structure. Internal structure. Do fishes have “senses”? A little about fish behavior.

Agnatha - “Jawless” Fishes Lamprey and Hagfish Closest relative to the first fishes that appeared 400 to 500 million years ago. 60 species alive today. Eel-shaped, no jaws, fins are smaller and reduced. Mouth modified for sucking – parasites.

Chondrichthyes - Cartilaginous Fishes Flexible skeleton of cartilage rather than bone. About 750 species living today. Well developed lower jaws, true bony teeth on both jaws. Sharks, skates, rays, ratfish. Scales similar to teeth – placoid scales.

Southern Stingray and Flounder at Gulf Specimens Marine Lab in Panacea, Florida. Can you find the eyes, the spiracles (for breathing), and the tail (where the spine is)?

Countershading

Osteichthyes - Bony Fishes Bony skeleton. More than 30,000 species of bony fishes. Flattened bony scales cover the surface of the body. Swim bladder: Air sac that helps the fish to change vertical position in the water. Some lay eggs, some have live births.

Spanish Mackerel Bay Anchovy Lookdown

This flounder can change its color to match its home This flounder can change its color to match its home! Why do you think that flounders do this?

This Gulf Flounder was not happy to be pulled up in a net This Gulf Flounder was not happy to be pulled up in a net! Where do you think that you would find this fish?

Things to Think About: What is the shape of the fish? What does the shape tell you about where the fish lives in the ocean? What kind of color pattern does the fish have? Camouflage? Countershading?

Body shape is related to the “lifestyle” of the fish! Flat=bottom Thin=rocks & vegetation Torpedo=open ocean & fast!

Examples of countershading in fishes, mammals, and birds.

Survey of Southeastern Fishes Fishes collected on the Georgia coast and the Florida Gulf coast.

Trumpet Fish

“Play dead” when alarmed (float motionless) mimicking floating leaves Batfish “Play dead” when alarmed (float motionless) mimicking floating leaves

Lion Fish

External Features Fins: Dorsal fin(s) Pectoral fins Pelvic fins Anal fins Caudal fin Shape and arrangement of fins is related to the “lifestyle” of the fish.

External Features (2) Lateral line: specialized cells that give the fish information about its position relative to other objects. The lateral line is well developed in schooling fish; it helps the fish swim together in a group without swimming into one another.

External Features (3) Operculum (gill cover) Gills Mouth Barbel (think about catfish & koi!) Eye Scales

Internal Anatomy Here are some of the things that you will find inside a fish: Gills (beneath the operculum) Swim Bladder Liver Stomach Intestine Gonad

Internal features of a bony fish compared with that of a cartilaginous fish. See any differences?

What do these things do inside a fish? Gills: Extract oxygen from the water. Swim Bladder: Allow the fish to change position in the water column, absent in sharks and rays. Liver: Filters toxins from the blood. Stomach: Digests food. Intestine: Absorbs digested food. Gonads: Make eggs or sperm in mature adults.

Fish Behavior In some fishes, males and females look different! The males are brightly colored while the females are drab. Why do you think that this happens? Fancy term for this: sexual dimorphism

Female Stoplight Parrot Fish Male Stoplight Parrot Fish Notice any differences?

Fish Behavior (2) In some fishes, the fish changes its sex as it gets older. Example: Black Sea Bass It is female first. This means that there are lots of small females to lay a lot of eggs. This means more bass! It becomes male toward the end of its life. The males are larger. Fewer males are needed because one male can fertilize a lot of eggs!

Fish Behavior (3) In seahorses, the female seahorse lays its eggs in the pouch on the male’s abdomen. The male seahorse actually incubates the eggs until they hatch.

Egg Pouch

Leafy Sea Dragon male carrying eggs

Fish Behavior (4) Some fish can dramatically increase their size when threatened. Puffer and spiny box fishes. Why do you think that the fish does this?

Fish Behavior (5) Some fish are very territorial. They guard their area and defend it by chasing off all intruders. Can you name a fish that does this? Why do you think that the fish behaves this way?

A Sailfin Goby uses large dorsal fin to scare off trespassers

What did you learn today? Where are fishes in the animal kingdom? Answer: vertebrates Name the three groups of fishes. Answer: jawless, cartilaginous, and bony