1. Fish Notes Sharks

2. Characteristics • Placoid scales – have a pointed tip which faces backwards. (denticles) • Heterocercal tail – upper lobe is longer than the lower lobe. • 3. Gill slits not covered by an operculum (5-7 gill slits) • Class: Chondrichthyes – skeleton made of cartilage & tooth-like scales covering their skin.

3. Characteristics, cont’d 4. Can’t swim backwards 5. Sharks have no swim bladder so they sink – to compensate they have a very oily liver – it can be up to 25% of their body mass. 6.Sharks vary greatly in size 7.Smallest –dwarf shark 6-8 inches Largest – whale shark 60 feet

4. Senses Teeth • some species can go through 20,000 teeth in a lifetime. • Broken teeth are replaced from those behind – like a conveyor belt.

5. Senses Ampullae of Lorenzini – hundreds of tiny holes in the face of a shark which helps them pick up electrical impulses given off by living prey items. Hearing – best sense – can hear prey in the water from 3,000 feet away. Lateral line – detects differences in water pressure to help fish detect obstacles in their path.

6. Senses Smell – well developed. They can detect 1 part blood per 100 million parts of water. 2/3rds of brain devoted to sense of smell Eyesight - certain sharks have evolved a special "nictitating membrane" on the lower lid of the eye that protects the eye from thrashing fish during feeding frenzies. They can see well in low light.

7. Shark Attack!! • Shark Attack – 25 species have attacked man • 3 most dangerous are Great White Shark, Tiger Shark and the Bull Shark • Chance of being attacked is less than being hit by lightning. • Most likely to attack in shallow water (less than 4 feet) • If attacked hit on nose or stick fingers in gills or eyes!