What is a Fish?• Fishes are aquatic vertebrates. Most fishes
have paired fins, scales, and gills.
Feeding and Digestion• Every mode of feeding is seen in fish –
herbivores, carnivores, parasites, filter feeders, and detritivores
Feeding and Digestion continued
• Complete Digestive Tract
– Food passes through the mouth and esophagus to stomach where digestion begins
Feeding and Digestion continued
• The pyloric ceca (cecum - singular)(fingerlike pouches) secretes digestive enzymes and absorbs nutrients from the digested food
Feeding and Digestion continued
• The liver secretes bile which helps break down fat
• The pancreas releases digestive enzymes into intestine
• The gallbladder stores bile and releases it to the intestine Gallbladder
• These are accessory organs, NOT part of the digestive tract
Feeding and Digestion continued
• The intestine completes the process of digestion and nutrient absorption
Feeding and Digestion continued
• Undigested material is eliminated through the anus
• Digestive Tract: M>E>S>I>A (write the words out) Accessory organs are not included.
Respiration• Most fishes exchanges gases with gills located
on either side of the pharynx
• Oxygen-rich water moves into the mouth and is pumped over gill filaments
• Oxygen-poor water is pushed out through openings in the sides of the pharynx
Circulation• Closed system – consists of heart, blood
vessels, and blood (duh)
• Delivers oxygen and nutrients to body cells
• Single-loop
– Heart pumps blood to gills where it picks up oxygen and releases carbon dioxide
– Blood moves to all body tissues then back to heart through veins
Circulation continued
• Most Fish hearts have 4 parts:
– Sinus venosus
– Atrium
– Ventricle
– Bulbus arteriosis
Sinus Venosus Atrium
VentricleBulbus arteriosus
Circulation continued
• Oxygen-poor blood from the veins collects in the sinus venosus
• Blood enters the atrium (one-way compartment) and flows to the ventricle
• The ventricle pumps blood into the bulbusarteriosus
• The bulbus arteriosus moves blood into the ventral aorta and toward the gills
Excretion• Kidneys filter chemical wastes from the blood
• Urine is formed in the kidneys and carried to urinary bladder where it is stored and later expelled
Urinary bladder
Excretion continued
• Kidneys help maintain homeostasis by varying the amount of water and salts in urine
– Saltwater fish – excrete very little urine but it is highly concentrated (little water)
– Freshwater fish – excrete large amounts of diluted urine (a lot of water)
Response/Nervous• Fishes have well-developed nervous systems
organized around a brain
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• The olfactory bulbs are involved with the sense of smell
• The cerebrum is responsible for the voluntary activities of the body – primarily processes sense of smell
• The optic lobes process information from the eyes
Optic lobe
Cerebrum
Response/Nervous continued
• The cerebellumcoordinates body movements
• The medulla oblongatacontrols the functioning of many internal organs
Cerebellum
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• Most have well-developed eyes and good color vision
• Good sense of taste and smell; may not hear sounds well
• Lateral line system allows fishes to sense vibrations in the water
• Some fishes can detect low levels of electric current
Movement• Most fishes move by contracting paired sets of
muscles on either side of backbone
• Force and action of the fins propel fish forward
• Fins are used to keep on course and adjust direction
Reproduction • Separate sexes; most show external fertilization
• Spawning (reproductive behavior) varies among different species
• Most lay large numbers of eggs to ensure some will be fertilized and survive
• Most fish are oviparous (lay eggs that hatch outside of body) ex. salmon
• Some species are ovoviviparous (eggs stay in mother’s body after internal fertilization) ex. guppies
• Some species are viviparous (give birth to live young) ex. sharks
Taxonomic Classification of Fishes
• Kingdom Animalia
• Phylum Chordata
• Subphylum Vertebrata
–Class Agnatha – jawless fishes
–Class Chondrichthyes – cartilaginous fishes
–Class Osteichthyes – bony fishes
Class Agnatha• “without jaws”
• Most primitive class of fish
• Lack jaws, paired fins, and scales
• Skeleton is made of cartilage
• Retains notochord as adults
• External fertilization
• Only has 2 living members: hagfish and lamprey
Hagfish
• Body Plan:
– Pinkish-grey
– wormlike bodies
– 4 or 6 short tentacles around mouths
• Found only in oceans (bottom dwellers)
• Detritivores – use a toothed tongue to scrape a hole in the dead or dying fish’s side
• Lack eyes but they have light-detecting sensors scattered around their bodies
Lamprey• Found in fresh
water and salt water
• Feeding
– Filter feeders as larvae
–Parasites as adults - suck up tissues and body fluids of hosts
• They have small eyes beneath skin
Class Chondrichthyes• “cartilage fish”
• Sharks, skates, rays
• Have jaws, paired fins, and cartilage skeleton
• Most are covered with placoid scales – feels like sandpaper
• Almost all live in saltwater
• Diverse feeding methods – most are carnivores; some are detritivores or filter-feeders
Skates and Rays• Flat body with paired pectoral fins behind heads
• Flat shape and coloration provide camouflage
• Mainly bottom dwellers
• Feed primarily on mollusks and crustaceans
• Largest rays are filter-feeders
Sharks• Teeth are replaced throughout their lives
–Go through as many as 20,000 in a lifetime
• Use several senses to locate prey
– Smell chemicals in the water
– Sharp vision in little light
–Well-developed lateral line system detects vibrations in water
• Most are carnivores, but larger species filter-feed
• Do not have swim bladders to control buoyancy (floating)
–Must keep moving (requires a lot of energy) OR
– Store lipids in liver to reduce density and provide buoyancy
• Internal fertilization
–Male uses claspers (modified pelvic fins) to transfer sperm to female
–Most are oviparous but some are ovoviviparous or viviparous
Sharks continued
Class Osteichthyes• “bony fish”
• Catfish, salmon, perch, bass
• Have jaws, paired fins, and skeletons of bone
• 3 key features
– Skeleton of bone – harder and heavier than cartilage
– Swim bladder – used to control buoyancy
– Scales – cover most bony fish; protects and helps reduce friction
• Largest class of fish (also largest class of vertebrates)
2 Groups of Bony Fish• Lobe-finned
– Fins are fleshy (like earlobes)
–Only 7 species exist today
– Includes lungfish
2 Groups of Bony Fish• Ray-finned
– Fins are supported by long, flexible bony structures (rays)
– Very diverse group
– Includes most familiar fish – eel, perch, bass, salmon
External Anatomy• Operculum – covers and protects gills
• Fins – increase stability and movement through water– Caudal fin (tail) – moves from side to side – helps
swim
– 2 dorsal fins and anal fin – keep fish upright and moving in straight line
– Pelvic and pectoral fins – used to navigate, stop, move up and down
• Skin – Most are covered with scales – minimize friction as
they swim
– Scales grow throughout life