Fishes

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

Movement & Response Endoskeleton Fins Swim bladder 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

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

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

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

Reproduction External fertilization Sharks, skates, & rays 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

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

Hagfish

Lamprey

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

Whale Shark

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