Fishes

1. Fishes

2. Characteristics • Most ancient vertebrates • Endoskeleton • Gills – gas exchange • Closed-loop circulation • Kidneys

3. Movement & Response • Endoskeleton • Made of either cartilage or bone • Fins • Increase stability; help turn, dive, or climb rapidly • Swim bladder • Gas-fill sac that allows them to regulate their vertical position in water • Variety of sensory organs • Sense light, smell, taste, sound, water vibrations • Lateral line (sense organ) • System of small canals lined with sensitive cells that detect vibrations in water

4. Respiration & Circulation • Gill – major respiratory organ • Made up of rows of filaments • Fingerlike projections through which gases enter & leave the blood • Hang between a fish’s mouth & cheeks • Gill slit • Opening at rear of a fish’s cheek • Countercurrent flow • Water passes over the gills in one direction as blood flows in the opposite direction through the gill’s capillaries • Allows oxygen to diffuse into the blood over the entire length of capillaries • Can extract up to 85% of the dissolved oxygen in the water passing over the gills

6. Respiration & Circulation • Single-Loop Blood Circulation • Simple chamber-pump heart • Blood collects in the atrium. • Heart’s ventricle pumps the blood back to the gills, completing a single loop • All fishes, except lungfishes, have single-loop circulation

7. Excretion • Gills and kidneys remove nitrogenous waste • Kidney – regulates body’s salt & water balance & removes wastes from the blood • Osmosis causes movement of water through membranes (such as gills & skin) toward regions of higher ion concentration. • Marine fishes lose water to their environment through osmosis • Ion (salt) concentration of sea water is 3 times that of most marine fishes’ tissues • Freshwater fishes have the opposite problem; their bodies contain more salt than surrounding water; taking in water by osmosis, diluting their body salts • Marine fishes excrete only a small amount of urine that has high salt concentration • Freshwater fishes excrete large amounts of dilute urine

8. Reproduction • External fertilization • Spawning • Male & female gametes released near one another in the water • May occur between two individuals or in large groups of males and females • Sharks, skates, & rays • Internal fertilization • Claspers • Male organs used to insert sperm into the female

9. Groups of Fishes • Jawless Fishes • Skeletons made of cartilage • Retain their notochord into adulthood • Only modern vertebrates without a backbone • Hagfish • Scavengers, predators that live at great depths • Lampreys • Parasitic, uses suction-cuplike mouth to attach to host

10. Hagfish

11. Lamprey

12. Groups of Fishes • Cartilaginous Fishes • Skeletons made of cartilage, strengthened by calcium carbonate • Sharks, skates, rays, ratfishes • Sharks • Teeth are modified scales, triangular in shape, arranged in 6-10 rows • Most are predators • Except whale shark (largest shark) consumes plankton • Skates & Rays • Flattened bodies adapted to life on the sea floor • Flattened teeth used to crush their prey

14. Whale Shark

16. Groups of Fishes • Bony Fishes • Strong endoskeleton made completely of bone • Structural adaptations • Lateral lines • Awareness of surroundings & detect objects in its environment • Opercula • Hard plate that covers the gills • Allows fish to move water over gills while remaining in one place • Swim bladder • Adjust the gas content to regulate buoyancy • Maintain or change its depth • Rays • Fins that are supported by bony structures