Icthologystudy of fish

Phylum Chordata• Subphylum Vertebrata

– Superclass Agnatha (jawless)• Class mixini – hagfish• Class cephalaspidomorphi – lamprey

HAGFISH LAMPREY

• Subphylum Vertebrata

– Superclass Gnathostomata (jaw mouth)

• Class Chondrichthyes – cartilage fish

–Subclass Elasmobranchi – sharks, rays, skate

• Class Osteoichthyes – bony fish

SKATE

SUPER CLSS AGNATHA

• Superclass Agnatha – 70 speciesGeneral Characteristics

1. Body – long, cylindrical (eel like)

2. No scales, jaws, or paired fins

3. Two chambered heart

4. 3-16 pairs of gills

5. poikilothermic – having a body temperature that varies with the temperature of its surroundings

– Hagfish • Marine, feed on dead or dying organisms (not

parasitic) • When caught, secretes enormous quantities of

slimy mucus• Enters body of an animal through gills, mouth, or

anus and eats the contents of the body leaving a sack of bones and skin

– Lamprey• 40 species, fresh and marine water, parasitic

• Reproduction (Hagfish and Lamprey)– Both ovaries and testes present, but only one is

functional– Males build nests in spring and fertilization is external

(2-65,000 eggs)– Adults die after spawning– Eggs hatch into larvae and burrow into sand or mud– Emerge at night to feed, blind and toothless– Larval form for 3-7 years– Metamorphosis into adult takes about 4-11 months

• Economic importance– Fish bait– Lamprey is food for humans

• FYI…• Portuguese and Spanish diners prize sea lamprey as a

gourmet treat for which they're willing to pay up to $25 a pound. European fishers harvested local lamprey so much that populations on that side of the Atlantic are crashing, allowing demand for this prehistoric boneless fish to exceed supplies.

• So what does lamprey taste like? "I would have to say it tastes like lamprey," says Chef Bob Bennett, "because it does not have a flavor that you can associate with anything else."

• When pushed further, he volunteered that "its taste is not offensive. A lot of delicacies that I've been introduced to over the course of my career are a lot less palatable - such as the sea urchin."

– Hagfish will damage fish caught in net or line

Some differences between sharks and fish

Sharks Fish

Made of cartilage Made of bones and cartilage

Can only swim forward Can swim forwards and backwards

Uses oil for buoyancy Uses gas-filled swim bladder for buoyancy

Eggs fertilized in females body Eggs fertilized in water

Skin is rough like sandpaper Slippery scales on skin

CLASS CHONDRICHTHYES

• External features– Head, trunk, tail

– Dorsal fins – keep upright– Caudal fins – forward thrust

• Heterocercal - dorsal lobe is larger than ventral• Homocercal – dorsal and ventral lobes are the same

size

– Pectoral and pelvic fins – steering

• Clasper – (male) on pelvic fin used in mating

They use one at a timeAfter communicating its intentions to a receptive female shark through ritualized swimming and gentle 'love nips' along her back or flanks, the male grasps one of her pectoral fins and docks next to her. If the male happened to dock along the left side of the female, he flexes his right clasper across the mid-line of his body and inserts it into her vent (genital opening).

MALE FEMALE

• Mouth – ventral • Eyes – lower lids to cover eye when feeding• Gill slits – 5-7 pairs; used for water to exit• Spiracle – modified gill slit on top of head

– Purpose: provide oxygenated blood directly to the eye and brain through a separate blood vessel.

– Absent or reduced in many sharks, especially the fast swimming sharks and is usually larger and present in bottom dwelling sharks. 

– In the rays, the spiracle is much larger and more developed and is used to actively pump water over the gills to allow the ray to breathe while buried in the sand.

• Vent- opening to cloaca; analogous to anus– Latin: “sewer”– Cloaca - common chamber that intestinal,

urinary, and genital tracts open. • FYI: It is present in amphibians, reptiles, birds,

sharks, and monotremes. A cloaca is not present in placental mammals or in most bony fishes.

Lateral line – sensory system detecting and locating objects

• Made of cells called Nematocysts (sensitive gel filled cells that transmit signals to nerves)

• Sensitive to vibrations and currents

• Ampullae of Lorenzini – gel-filled pores on face– sense bioelectric fields– A biolelectric field surrounds all animals. Sharks can

even detect animals under the sand!– It looks like a 5 o’clock shadow

• Placoid scales – backward pointing spine covered by enamel

• Skeleton – cartilage– Axial – skull and vertebral column– Appendicular – pectoral girdle (front fins) and pelvic

girdle (pelvic fins)

• Digestive system

– Mouth– Teeth -replaced throughout life of fish– Tongue -immobile– Esophagus -short– Stomach -J shaped– Pylorus -valve– Intestine -spiral valve– Cloaca -common chamber– Vent -anus– Liver -very large, oily, purifies blood– Gall bladder -near top of liver, stores bile collected from

liver and passes bile to intestines through bile duct– Pancreas – between stomach and intestine, secretes

digestive enzymes that are released into intestine– Rectal gland – located near most posterior part of

abdominal cavity; regulates excess salt received from food and water

• Coelom– Peritoneum – lining the abdominal cavity

• Made of layers– Outer layer - parietal peritoneum, is attached

to the abdominal wall– Inner layer - visceral peritoneum, is wrapped

around the internal organs located in inside the abdominal cavity

• Mesenteries – membranes that attach organs to the abdominal wall, hold intestine in place

• Circulatory System– Sharks have a two-chambered heart, with an atrium (aka

auricle) and a ventricle. – Heart is covered by a visceral pericardium– The heart is S-shaped– ventral aorta transports blood to the gills – dorsal aorta takes blood back to the heart

– Vessels• Carotids – carry blood to and from head• Subclavians – carry blood to and from pectoral fins

» Meaning “subclavical”, under the clavical• Renal – carry blood to and from kidneys

» Have you ever heard of renal failure in cats? Renal is from the Latin word renes which means kidneys

• Iliacs – carry blood to and from pelvic fins» From the Latin word ilia describing the bones that make

up the pelvis

Some Review

1. Sketch a shark: LABEL the Anterior dorsal finPosterior dorsal finHomocercal caudal finPelvic finPectoral fin

2. What is the function of the spiracle?

3. What is the function of the ampullae of lorenzini?

4. Why do sharks have a large liver?

5. What is the function of the clasper?

6. What is the function of the cloaca?

9. What kind of fish eats out the insides of a dead organism?

10. What class do sharks belong to?

11. What class do bony fish belong to?

12. What shape is the sharks stomach?

13. How many chambers are in a sharks heart?

1. Sketch a shark: LABEL the Anterior dorsal fin

Posterior dorsal fin

Homocercal caudal fin

Pelvic fin

Pectoral fin

2. What is the function of the spiracle?Provide oxygenated blood directly to eyes and brain

3. What is the function of the ampullae of lorenzini? Sense bioelectric field

4. Why do sharks have a large liver? Produces oil

5. What is the function of the clasper? Reproduction (male part)

6. What is the function of the cloaca? Common chamber for intestines, urinary, and genitial

9. What kind of fish eats out the insides of a dead organism?

hagfish

10. What class do sharks belong to? Chondrichthyes

11. What class do bony fish belong to? Osteoichthyes

12. What shape is the sharks stomach? J

13. How many chambers are in a sharks heart? two