Class Agnatha

•80 species of hagfishes and lampreys•Skin lacks scales and plates•Cartilaginous skeleton, unpaired fins•Notochord remains throughout life•Some are parasitic•Hagfishes are marine; most lampreyslive permanently in fresh water•All lampreys reproduce in fresh water

Figure 34.8 A hagfish

Figure 34.9 A sea lamprey

Class Chondrichthyes

Includes:SharksRaysSkates

Figure 34.11 Cartilaginous fishes (class Chondrichthyes): Great white shark (top left), silky shark (top right), southern stingray (bottom left), blue spotted stingray

(bottom right)

Class Chondrichthyes

•Skeletons are made of cartilage•Skin is covered with placoid scales

Sharks•Mouth contains 6-20 rows ofteeth that point inward; when they break or wear down, the others move forward

•Paired nostrils on the snout have specialized nerve cells that connect with olfactory bulbs of the brain

•Largest brain of all fish

Adaptations of Cartilaginous Fish•Most pump water over their gillsby expanding and contracting their mouth cavity and pharynx

•Rays and skates have spiracles located behind their eyes

•Ammonia is converted to urea, which is much less toxic

•Swimming generates lift and many cartilaginous fish can store large amounts of low-density lipids in their livers to maintain buoyancy

Reproduction in ChondrichthyesFertilization is internal, a male transfers sperm using a modified pelvic fin called a clasper.

Sensory Functions•The lateral line system is present in nearly all fish, which is a row of sensory structures that runs the length of the fish to detect vibrations in the water

Class Osteichthyes – Bony FishCharacteristics:•Bones•Lungs or Swim Bladder

Lungfishes have gills and lungs

** All bony fish have an operculuma hard plate that opens at the rearand covers and protects the gills•Scales

Lobe-Finned Fishes

•Have fleshy fins that are supported by a series of bones•7 species of lungfishes and one species of coelocanth exist today

• The lungfish resembles a short bodied eel. The base color of the fish is brown with small spots all over.

• They are carnivores. The dorsal and anal fins are long-based.

Figure 34.14 A coelocanth (Latimeria), the only extant lobe-finned genus

Ray-Finned Fishes

•Have fins that are supportedby long, segmented, flexiblebony elements called rays.•includes eels, perch, salmon, guppies, bass

Figure 34.13 Anatomy of a trout, a representative ray-finned fish

Figure 34.12a Ray-finned fishes (class Actinopterygii): yellow perch

Respiratory and Circulatory Systems

•Water flows away from the head and the blood flows toward the head. This countercurrent flow allows more oxygen to diffuse into the gills•Fish regulate their overall density by adjusting the amount of gas in their swim bladders•There are four chambers in the heart

Buoyancy in Fish

Squalene (liver oil)

Buoyancy in Fish

Buoyancy in Fish

Physoclistous bladder

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Respiration in Fish

Respiration in Fish

Osmoregulation in Fish

Reproduction

•Fertilization in most species is external

•If internal fertilization occurs, the maleinserts his sperm into the female usinga modified anal fin; the female carries the eggs inside her until the young are born

Diadromous - fish that make “two runs” in their life to live and reproduce

Anadromous - fish that “run up” - salmon

Catadromous - fish that “run down” - eels

Parthenogenesis - no males required, females produce diploid eggs - Amazon molly

Fish Reproductive Adaptations