Fish

From Myxini to Dipnoi

Jennifer Zhang & Larry Wang

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Phylum

• Phylum Chordata• Major clades:

– Myxini (hagfishes)– Cephalaspidomorphi (lampreys)– Chondrichthyes (sharks, rays)– Actinopterygii (ray-finned fishes)– Actinistia (coelacanths)– Dipnoi (lungfishes)

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Sample Species

• Hagfish• Sea lamprey• Great white shark, sting ray• Clownfish, sea horse, angel fish, tuna• Coelacanth• Lungfish

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Lamprey (Cephalaspidomorphi)

Hagfish (Myxini) Angelfish (Actinopterygii)

Sting ray (Chondrichthyes)

Coelacanths (Actinistia)

Lungfish (Dipnoi)

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Body Cavity

• All phyla are coelomates

• Fluid filled body cavity called a coelom

• Complete lining developed from the mesoderm

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Body Symmetry:

Bilateral

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Nervous System

• Well developed nervous system• Possess central nervous system

consisting of brain and spinal cord• CNS functions to control muscle

movements and maintain homeostasis

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Sensory

• Possess highly developed sensory organs• Possess specialized chemoreceptors

resulting in good sense of smell and taste• Many have eyes with color vision• Lateral line system (microscopic organs)

allows fish to detect vibrations and currents• Some fish can detect electric currents

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• Gills located on either side of pharynx

• Made up of filaments which are networks of capillaries that allow gas exchange

• Blood in the capillaries flows in the opposite direction of the water

• Push oxygen poor water out of gills

• Some fish have lungs and can breathe air

Respiratory System

Circulatory System • Closed circulatory system (+open for myxini)

– Blood closed to within vessels at all times

• Blood travels: heart gills rest of body heart. • Blood flows to gills through the aorta • Two chambered heart, four parts:

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• Food is ingested through mouth• Digestion begins in esophagus • Stomach breaks down food further• Many fishes have pouches called cyloric

caeca to further aid in digestion• Intestine completes the process

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Digestive System

Excretory System

• Release nitrogenous wastes as ammonia• Wastes can diffuse through the gills into

surroundings • Kidneys also control the amount of ammonia

in their bodies• Saltwater fish lose water due to osmosis.

– Kidneys concentrate wastes returning as much water as possible back to the body

• Freshwater fish gain water continuously– Kidneys pump out large amounts of dilute urine

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Musculature/Locomotion• Possess muscles that

function in locomotion• Swim by exerting force

against water• Contract sets of muscles on

sides of body alternately• Generate S-shaped waves of

flexion that move down the body

• Move forward to force exerted backwards

• Swimmer bladders (gases) and liver (oil helps keep fish afloat)

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Skeletal Type

• Three main components:– spine– the skull– Appendicular skeleton

• Notocord: flexible rod that provides skeletal support throughout body/ provides muscles something to work against when swimming

• Composition includes cartilage

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Reproduction

• Sexual reproduction-lay eggs! • Some are hermaphrodites• Have ovaries and testes • Larval stage (except myxini) • Oviparous

– Eggs released outside mother’s body • Ovoviviparous

– Fertilized eggs are retained in oviduct • Viviparous

– Young develop in the uterus

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Miscellaneous

• In the world of molecular systematics there is no such thing as fish (some are genetically more related to mammals than other scaled aquatic chordates)

• Most lampreys are parasitic and feed off live fish by clamping on to them with their jawless mouth.

• Sharks don’t have ear drums but sound reaches them through water

• About 15,000 fish haven't even been identified yet!

Quiz• What do hagfishes lack that all other fish

have?– Vertebrae

• What nitrogenous chemical do fish secrete?– Ammonia

• What organ system allows fish to detect vibrations?– Lateral Line System