Chapter 41: Fishes

41-1 Introduction to Vertebrates

41-2 Jawless Fishes, Sharks, and Rays

41-3 Bony Fishes

I. Characteristics of Vertebrates (evolved ~ 550 m.y.a.)• Possess VERTEBRAE (protect DORSAL nerve cord), a CRANIUM (skull), and ENDOSKELETON (bone or cartilage)

41-1 Introduction to Vertebrates

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(1) Vertebrate Column• Spinal column or BACKBONE that protects spinal cord.

(2) Cranium• Skull encases and protects the BRAIN.

(A) Classification (~ 45,000 species vertebrates, MOST are fishes)• SEVEN classes occupying TERRESTRIAL and AQUATIC habitats.

(1) Lampreys and Hagfishes (~ 80 species)• Elongated, eel-like cartilaginous bodies LACKING jaws, paired fins, and bone.

(2) Sharks, Rays, and Skates (~ 800 species)• Predatory fishes have JAWS, PAIRED FINS, skeletons of CARTILAGE, and a unique type of SCALE (integument).

(3) Bony Fishes (~ 23,000 species)• Jaws, BONY skeleton; TWO bony fish lineages—(1) RAY-Finned Fishes (most species), (2) LOBE-Finned Fishes.

(4) Amphibians (~ 4,500 species)• Thin, MOIST skin permeable to GAS exchange; LAY eggs IN WATER and pass through an aquatic LARVAL stage.

(5) Reptiles (~6,000 species)• Dry, SCALY skin with leathery eggs laid ON LAND, protected against desiccation.

(6) Birds (~ 10,000 species)• Adaptations from reptiles allowing FLIGHT include feathers, HOLLOW bones, and unique RESPIRATORY system.

(7) Mammals (~ 4,400 species)• Presence of INSULATING hair or fur and OFFSPRING are nursed with MILK from mammary glands.

II. Evolution (~ Evolution from Acanthodians, Chordates 550 m.y.a.)• EARLIEST appeared shortly after 1st chordates; ~ early JAWLESS fishes had HEAVY, bony scales; (i.e., Class Agnatha)

(A) Origin of Jaws (evolved ~ 440 m.y.a., out-competing jawless ancestors)• Evolved from GILL ARCHES as an adaptation favoring IMPROVED methods of obtaining nutrition (i.e., improved PREDATION)

(1) Gill Arches (1st pair evolved into JAWS)• Skeletal elements SUPPORT pharynx and evolved into first JAWS.

I. Life in the Water (adaptations)• Streamlined, muscular tail, paired AND unpaired fins, MUCUS coating, air bladder, and vascular GILLS.

41-2 Jawless Fish, Sharks, and Rays

(1) Many species of fishes that live deep in the ocean, where there is little or no light, are luminescent. What might be the advantages and disadvantages of such an adaptation?

Critical Thinking

(A) Homeostasis (freshwater VS. marine species of fish, osmosis)• KIDNEYS and GILLS filter blood, regulate ION concentrations (Na, K), and RELEASE wastes.

(2) Saltwater fishes drink more water and produce much less urine than freshwater fishes do. How could you account for this difference?

Critical Thinking

(B) Sensory Functions (vary by species)• Detect VIBRATIONS, and developed senses of SMELL, sight, hearing, and ELECTRICAL currents.

(1) Lateral Line System (detects VIBRATIONS in the water)• A row of SENSORY organs run length of body on EACH SIDE connected by NERVES to BRAIN.

II. Class Agnatha (~ 80 species)• Jawless fish LACKING vertebrae freshwater AND marine habitats.

(A) Hagfishes (LACK vertebrae, retain notochord ~ cold, marine waters)• Burrow into body of a DEAD or DYING fish through gills, skin, or anus and EAT internal organs. (i.e., NON-parasitic)

(B) Lampreys (all breed in freshwater, BUT may inhabit marine waters)• PARASITIC require HOST to draw BLOOD from an inflicted WOUND.

(3) When sea lampreys invaded the Great Lakes, they devastated populations of their hosts. In lakes where sea lampreys have lived for a long time, host populations have NOT declined. Using what you understand about co-evolution, explain why this disparity may exist.

Critical Thinking

(1) External Fertilization• NEST is dug out of gravel and EGGS are released (fertilized by sperm, hatching into LARVAE resembling lancelets, develop into ADULTS).

II. Class Chondrichthyes (~ 800 marine species)• CARTILAGINOUS fishes ~ sharks, skates, and rays with JAWS, skeletons, and paired FINS.

(1) Cartilage• A flexible, LIGHT-WEIGHT material made of cells surrounded by tough fibers of PROTEIN.

(2) Placoid Scales (a.k.a., “denticles”)• Small, tooth-like scales (sandpaper) REDUCES friction of water during swimming. (BUT limits diffusion through skin)

(4) Sharks have a large corkscrew-shaped structure in the intestine called a “spiral valve”. How do you suppose this organ might function in digestion?

Critical Thinking

(A) Sharks (use smell, lateral lines, vision, and electrical fields to hunt)• Predatory (tiger shark, bull shark) or filter-feeders (whale shark, basking shark) with senses (LARGEST brains of all fish) and REPLACEABLE teeth.

(5) In a famous set of experiments, A. J. Kalmijn studied the ability of sharks to find prey. He showed that a shark could locate and capture a stationary fish buried in the sand at the bottom of a tank. When the fish was enclosed in electrical insulation and then buried, however, the shark could not locate it. From this information alone, can you conclude that the shark is using only its electrical sense to locate the buried fish? Explain your answer.

Critical Thinking

(1) Pectoral Fins (increased stability AND maneuverability of fish)

• PAIRED fins behind head on VENTRAL side used for BALANCING.

(2) Olfactory Bulbs (pick up SCENTs)• Connect brain to nerve cells within NOSTRILS on snout monitor CHEMICALS in water, especially URINE and BLOOD.

                                                                                                         

TOP BOTTOM

(B) Rays and Skates (BOTTOM dwellers feed on mollusks and crustaceans)• Flattened bodies with paired WING-like PECTORAL fins, and in some cases, WHIP-like tails.

(C) Adaptations of Cartilaginous Fishes• Gills and spiracles CONVERT ammonia to urea (less toxic, storable, no need to drink as OAS levels are matched—body = ocean);

• Breathe by SWIMMING (spiracles) OR just by EXPANDING and CONTRACTING their mouth cavity (gills).

(1) Rectal Gland• Removes EXCESS ions from blood and RELEASES them into rectum.

NOTE: BUOYANCY is maintained via SWIMMING (generates upward LIFT) and low-density LIPID storage in the LIVER (oil FLOATS in water), REDUCING body density (an NRG saver).

(D) Reproduction of Cartilaginous Fishes• DIFFER from jawless fish in that fertilization is INTERNAL in female.

(NOTE: Yolky egg can be LAID or RETAINED—live birth)

(1) Internal Fertilization• Females lay large, yolky eggs after fertilization; young develop within egg (nourished by yolk) AND hatch as juveniles. (NO parental care given)

(2) Claspers (ONLY found in MALES)• During MATING, male transfers sperm INTO female’s body with MODIFIED PELVIC fins and may BITE the fin to HOLD ON.

I. Characteristics of Bony Fishes (~ 24,000 species, 2 groups)• Inhabit freshwater AND marine habitats; ~ 3 key features.

41-3 Bony Fishes

(6) Cod and many other ocean fishes lay eggs near the surface of the water. The male largemouth bass scoops out a nest in a lake or river bottom and waits for a female to deposit her eggs. What hypothesis would you make regarding the relative number of cod and bass eggs? Explain your answer.

Critical Thinking

(1) Bone (calcified)• Harder AND heavier than cartilage; ENDOSKELETON.

(2) Lungs (early bony fishes) or Swim Bladder (gas filled sac)• Gas exchange in a few LUNG fishes; MOST use bladder for BUOYANCY (i.e., modified lung)

(7) Bottom-dwelling fish often lack a swim bladder. Explain the adaptive advantage of this adaptation.

Critical Thinking

(3) Scales• Protect AND reduce water FRICTION while swimming.

(A) Lobe-Finned Fishes (~ 6 species of lungfish, 1 species of coelacanth)• Fleshy fins supported by bone; (NOTE: Lobe-finned fishes are believed to be ANCESTORS of amphibians and all other terrestrial vertebrates).

(B) Ray-Finned Fishes (~ MAJORITY of bony fishes)• Fins supported by long, flexible BONY rays;

(Fins do NOT have a central bony axis)

II. External Anatomy• Yellow PERCH is ~ bony fish; head, trunk and tail regions.

(1) Operculum (located on EACH side of the head)• Hard COVERING opens at rear and PROTECTS gills.

(A) Fins (FOUR types)• For swimming (propulsion, steering, and balance).

(1) Caudal Fin (tail fin)• Moves from side to side PROPELS the body.

(2) Dorsal Fins (back fins)• Keeps fish UPRIGHT and moving in a STRAIGHT line.

(3) Anal Fin• Ventral fin works with dorsal fins for BALANCE.

(4) Pelvic Fins• Paired with PECTORAL fins to steer, stop, move up/down, and back up.

(B) Skin (covered with scales)• Thin, round disks of a bone-like material grow from pockets in skin.

III. Internal Anatomy• Protected by skeleton—skull, spinal column (vertebrae with cartilage pads), pectoral girdle, pelvic girdle, and ribs.

(1) Pectoral and Pelvic Girdles (fin support)• Attachment points for FINS in to skeleton.

(A) Digestive System• Jaws are designed to GRIP and TEAR prey.

(1) Esophagus• CONNECTS mouth to stomach.

(2) Stomach• Secretes acid AND digestive enzymes.

(3) Intestine• Nutrients ABSORBED into bloodstream.

(4) Liver• Makes and secretes BILE into gall bladder.

(5) Gall Bladder• Stores AND releases BILE into intestine for lipid digestion

(emulsifies fats).

(6) Pancreas• Makes AND releases digestive enzymes into intestine.

(7) Anus• Eliminates undigested food material FROM intestines.

(B) Circulatory System

• Carries O2, CO2, nutrients, NH4 throughout body (e.g., consists of 4-pseudo-chambered heart)

(1) Arteries (AWAY from heart)• Carry blood pumped FROM heart to capillaries.

(2) Capillaries (SITES of exchange)• Thin-walled TINY vessels where GAS EXCHANGE occurs.

(3) Veins (TOWARD the heart)• Returns blood from the body back TO heart.

(5) Atrium (Chamber 2—TRUE CHAMBER)• FORCES blood into muscular VENTRICLE, main pumping chamber.

(6) Ventricle (Chamber 3—TRUE CHAMBER)• FORCES blood THROUGH GILLS and BODY with GREAT pressure.

(7) Conus Arteriosus (Pseudo-Chamber 4)

• Uses valves to PREVENT blood from flowing BACKWARD into ventricle; (smoothes flow of blood from heart).

(4) Sinus Venosus (Pseudo-Chamber 1)• Receives d-Blood from body.

(C) Respiratory (gills AND gill rakers) and Excretory System• Water pulled into mouth AND pumped OVER gills, before EXITING behind operculum.

(1) Countercurrent Flow (water flows away from head, blood toward head)• Blood in capillaries AND water flow in OPPOSITE directions (i.e., This optimizes the diffusion of oxygen INTO the blood)

(2) Urine (made from kidneys filtering blood)

• CONTAINS NH4, ions, and water.

(3) Urinary Bladder• Stores urine UNTIL it is excreted.

(D) Swim Bladder• GAS in this thin-walled abdominal SAC, enabling RISING or SINKING.

(E) Nervous System• Brain, spinal cord, peripheral nerves connecting to SENSORY organs.

(1) Cranial Nerves• Connect SENSORY organs with brain through FORAMEN in the skull.

(2) Cerebrum (part of the FOREBRAIN)• Integrates sensory data from OTHER parts of brain.

(3) Optic Tectum (dominates midbrain)• Receives & processes info—visual, auditory, and lateral line systems.

(4) Cerebellum (part of the HINDBRAIN)• Helps to coordinate fish’s motor output (locomotion AND balance)

(5) Medulla Oblongata• Regulates body functions AND relay station for senses.

(6) Spinal Nerves• Connect SPINAL CORD with organs, muscles, and senses.

(F) Reproduction (an “egg-layer” is described as being “OVIPAROUS”)• Majority ~ EXTERNAL fertilization with eggs laid OUTSIDE body.

(1) Spawning (with EXTERNAL fertilization)

• Reproductive EGG-LAYING behavior influenced by NESTING sites.

Extra Slides AND Answers for Critical Thinking Questions

(1) Fishes that have lived a long time with lampreys have evolved ways to protect themselves. The Great Lakes fishes had not yet done so.(2) The spiral valve probably increases the surface area available for the absorption of nutrients.

(3) The experiment does not exclude the possibility that sharks are finding their prey by smell. Although the insulating material would block electrical signals from the prey fish, it might also block the fish’s odor. (In fact, Kalmijn conducted further experiments to demonstrate that sharks could detect the fish by its electrical discharges only. (4) The body fluids of a freshwater fish have a higher concentration of ions than does fresh water. Thus, freshwater fishes gain water and rid themselves of this water by producing large amounts of urine. They do not need to drink. Saltwater fishes, by contrast, have lower ionic concentrations than sea water, so they lose water. They must drink to replace this water, and they conserve water by producing little urine.

(5) Because swim bladders help fishes float, a bottom dweller would be disadvantaged if it did float.

(6) It probably attracts desirable prey.

(7) It is likely that the bass would produce fewer eggs for two reasons. First, because it provides some protection for its eggs, their mortality likely will be lower. Fewer eggs will be lost and need to be replaced. Second, because the bass invests more in each egg, it does not have the resources to produce as many eggs.