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Chapter 10Chapter 10Marine FishesMarine Fishes

Fishes and Other Vertebrates• Fishes are vertebrates—animals that

possess vertebrae, a series of bones or cartilages that surround the spinal cord and help support the body

• Primitive fishes lacked paired fins and jaws

• Adaptation of jaws and paired fins allowed fish to more efficiently obtain food ultimately replacing all but a few jawless forms.

Jawless Fishes

• Hagfish - lampreys• Lack both jaws and paired appendages• Have skeletons of cartilage (no bone)• Lack scales• Hagfish also lack vertebrae

Hagfishes

• Bottom dwelling “slime eels”

• Skins are used to make leather goods

• Slime glands produce abundant milky, gelatinous fluid for protection if hagfish is disturbed

Lampreys• Have oral disk and rasping tongue covered with

horny dentacles to grasp prey, rasp hole in the body and suck out tissue and fluid.

Cartilaginous Fishes

• Class Chondrichthyes– e.g. sharks, skates, rays, chimaeras

• Skeleton of cartilage

• Possess jaws and paired fins

• Placoid scales cover skin

Sharks• Top predators of ocean’s food webs• Excellent swimmers with streamlined

bodies– swim with powerful, sideways sweeps of the

caudal fin (tail)– heterocercal tail: caudal fin in which the dorsal

lobe is longer than the ventral

• Males have claspers—modified pelvic fins which transfer sperm from the male to the female

Caudal fin

Clasper Pelvicfin

Rectalgland Spleen

Cloaca

Dorsal fin

Intestine

KidneySpine

Stomach Testis Gill slits

Mouth

PharynxHeart

Pectoral fin

Liver

Pancreas

Placoidscales

Stepped Art

Fig. 10-3, p. 266

Sharks

• Ventral mouth with multiple rows of teeth which are constantly replaced

• Found in all oceans with the greatest numbers in temperate and tropical waters

• Humans exploit shark populations for fins, meat, oil, leather, cartilage and sport

Skates and Rays• Have flattened bodies adapted to a bottom

existence• Greatly enlarged pectoral fins that attach to the

head• Reduced dorsal and caudal fins• Eyes and spiracles (openings for the passage of

water) on top of the head• Gill slits on the ventral side• Lack anal fin• Specialized teeth are used to crush prey (e.g.

benthic invertebrates)

• Electric rays have electric organs that can deliver up to 220 V

• Stingrays have hollow barbs connected to poison glands– treatment for stingray wounds: submerge in hot water to

break down protein toxin

• Sawfishes and guitarfishes have a series of (non-venomous) barbs along their pointed rostrums

• Fished commercially for food, many are considered threatened

Skates and Rays

Lobefins

• Coelacanths – classified as lobefins due to presence of rod-shaped bones surrounded by thick muscle in the pelvic and pectoral fins

• Only known as fossils until discovery of living specimen in 1938

Lobefins• Live in Indian Ocean at depths of 150 to 250

meters• Skeleton made of bone and cartilage (vertebral

column is cartilage)• Rostral organ in head detects weak electrical

currents, may aid in prey detection• Life span is 60 years, reach sexual maturity at ~ 20

years, produce 5 to 26 live young• Considered to be in danger of extinction

Ray-Finned Fishes• Possess unpaired and paired fins,

providing better control of movements• 1 or more dorsal fins, caudal fin, and

usually anal fin– help maintain stability while swimming

• Paired fins consist of pectoral and pelvic fins– both used in steering– pectoral fins also help to stabilize the fish

The Biology of Fishes: Body Shape

• Shape of body determined by characteristics of habitat

• Fusiform body shape: streamlined shape with a very high and narrow tail– efficient movement for active swimmers

Body Shape• Laterally

compressed or deep body– allows

navigation through

complex habitat, e.g., grass or corals

Body Shape

• Depressed or flattened bodies– bottom-dwelling fishes

Body Shape

• Globular bodies, enlarged pectoral fins– appropriate for sedentary lifestyle

Body Shape

• Long, snake-like bodies, absent or reduced pelvic and pectoral fins– useful for burrowing, living in tight spaces

Fish Coloration and Patterning

• Countershading is seen in open ocean fish– when viewed from above, dark color blends in

with surrounding water; when viewed from below, white belly blends in with lit surface waters

• Disruptive coloration—background color of the body is usually interrupted by vertical lines; may be a dark dot (“eyespot”) present in tail area– more difficult for predators to see the fish

Fish Coloration and Patterning

• Poster colors: bright, showy color patterns– may advertise territorial ownership, aid

foraging individuals to keep in contact, or be important in sexual displays

– warning coloration: bright coloration to warn predators that the fish is too venomous or spiny to eat

Fish Coloration and Patterning

• Cryptic coloration: coloration which blends with the environment– used for camouflage

Locomotion – muscles contract alternately from one side of

the body to the other

Locomotion

• Fish with different body forms swim in different ways– elongate fish undulate the entire body– swift swimmers flex only the posterior portion of

the body– other fish are somewhere in between– fish with a dermal skeleton can only flex the area

before the caudal fin– some fish swim using their fins alone without

body flexure

The Biology of FishesRespiration and Osmoregulation

• Gills often used to extract O2, eliminate CO2, and aid in salt balance

– gill filaments: highly vascularized, rod-like structures which compose the gills

Gillrakers

Gillfilaments

Operculum (gill cover)

Water+

CO2

Deoxygenatedblood

enteringgill

Oxygenatedblood leaving gill

Waterand O2

Waterand CO2

Gillfilament

Bloodcapillaries

Water+O2

Deoxygenatedblood entering

gill

Bloodflow

Stepped Art

Fig. 10-21, p. 278

Respiration and Osmoregulation

• Water must be continuously moved past the gills to keep blood oxygenated– most ray-finned fishes ventilate gills by

pumping water across them using gill pumps– very active fishes, e.g., sharks, tuna, and

swordfish use ram ventilation—continuously swimming forward at high velocity with the mouth open

Respiration and Osmoregulation

• Osmoregulation refers to process by which organisms maintain proper concentration of solutes and water in body fluids

• Blood’s salt concentration is about 1/3 that of seawater, so water is lost

• Fish drink seawater to compensate

Drinkssalt water Small volume of

isotonic urine

Water loss by osmosis

Water gain by osmosis

Somesalt waterswallowedwith food

Large volume ofhypotonic urine

Salts diffuse inthrough gills

Kidney withlarge glomeruli—reabsorbs urea

Salt-excretinggland

Kidney with smallor no glomeruli

Gains saltsby diffusion

Salt excretedthrough gills

Stepped Art

Fig. 10-22, p. 279

The Biology of FishesCardiovascular System

• Consists of heart, arteries, veins, and capillaries

Cardiovascular System– maintain body-core temperature at 2-10oC

above seawater, increasing efficiency of swimming muscles

The Biology of FishesBuoyancy Regulation

• Maintaining buoyancy– sharks sink if they stop swimming– large livers produce squalene—an oily material

with a density less than seawater

Buoyancy Regulation

• Most fish use a swim bladder—a gas-filled sac that helps offset the density of the body and regulates buoyancy– the fish can adjust the amount of gas in the

swim bladder to maintain depth

Buoyancy Regulation• Active swimmers do not have swim

bladders, and must swim to avoid sinking• Bottom dwelling fish lack swim bladder, do

not need to maintain buoyancy in water column

The Biology of FishesNervous System and Senses

• Nervous system consists of: brain, spinal cord, peripheral nerves, and various sensory receptors

• Olfaction and Taste– olfactory receptors in sharks (“swimming noses”)

well developed– ray-finned fishes have olfactory pits—blind sacs

opening to the external environment that contain olfactory receptors

– taste receptors may be located on the surface of the head, jaws, tongue, mouth and barbels (whisker-like processes about the mouth)

Nervous System and Senses

• Lateral line system and hearing– ray-finned fishes have a lateral line system for

detecting movement in the water – aids in locating prey and avoiding predators

– lateral lines consist of canals running along the length of the fish’s body and over the head

Nervous System and Senses

• Lateral line system and hearing– ears are internal and have a detection range

of 200 to 13,000 hertz• human range = 20 to 20,000 hertz

Nervous System and Senses

• Vision– no eyelids (or poorly developed)– usually don’t need to adjust pupil size

because of the low quantity of light– eyes are usually set on the sides of the head– shallow-water species can perceive color

Nervous System and Senses

• Ampullae of Lorenzini– organs scattered over the top and sides of

shark (and relatives) head – sense electrical currents in water

The Biology of Fishes: Digestion

• Digestive system consists of mouth, pharynx, esophagus, stomach and intestine

Digestion

• All cartilaginous fish are carnivores

• Ray-finned fishes exploit all food resources and can be carnivores, herbivores or omnivores

• Prey of carnivorous fish is swallowed whole, chewing would block water flow past gills

• Filter feeding fish (e.g., basking sharks) use gill rakers to filter plankton

The Biology of FishesAdaptations to Avoid Predation

• Many exhibit elaborate camouflage

• Pufferfishes and porcupinefish inflate their bodies to deter predators

• Flying fishes use enlarged pectoral fins to glide through the air and escape

• Parrotfish secrete a mucus cocoon

• Surgeonfish are armed with razor-sharp spines

Adaptations to Avoid Predation

• Clingfishes use a sucker to attach to rocks so predators can’t dislodge it

• Triggerfish projects spines to deter predators or wedge itself into cracks

• Scorpionfish and stonefish have venom glands for self-protection

The Biology of Fishes: Reproduction

• Sexes are typically separate• Sperm and eggs pass to the outside through

ducts

Reproduction • Three reproductive modes:• Oviparity – eggs are shed into the water column

and embryo develops outside the mother’s body– common in ray-finned fishes

• Ovoviviparity – fertilization is internal and eggs hatch within mother’s uterus, where they are nourished by yolk stored in egg– common in sharks

• Viviparity – young attach directly to mother’s uterine wall or uterus produces “uterine milk” that is absorbed by embryo– occurs in some sharks and some ray-finned fishes

• Hermaphroditism: individuals have both testes and ovaries at some time in their lives– occurs in at least 14 bony fish families– synchronous: possessing functional gonads of

both sexes at one time– sequential: changing from one sex to another

Reproductive Strategies

The Biology of Fishes: Schooling

• School of fish = group of individuals that operates in a polarized, synchronized fashion

• Reasons for schooling:- more eyes increases food finding abilities and

predator avoidance- predators can’t focus on an individual

The Biology of Fishes: Fish Migrations

• Daily migrations usually associated with feeding and predator avoidance

• Seasonal migrations usually associated with spawning, changing temperatures or feeding

• Migrations may occur within seawater or between seawater and fresh water to spawn