Transcript The Problems of Fish

The Problems of Fish
Oceans 11
Introduction
• Seawater may seem like an ideal
habitat, but living in it does present
difficulties.
–
–
–
–
How can fish best move through water?
Why don’t fish sink?
How can fish breath underwater?
How do they deal with the salinity of
seawater?
– How can predators be avoided?
Movement Shape and
Propulsion:
• How can fish best move through water?
– Fish usually have a streamlined shape (this
reduces energy loss to drag)
– Faster swimming fish have tapered, torpedo like
body plans
– Swimming occurs by S-shaped waves that pass
through body.
• *FYI - Swordfish and Marlin can reach speeds
of 120km/hr!
• http://www.youtube.com/watch?v=Viu9gql
djrc&feature=related
Bluefin Tuna
Maintenance of Level:
• Why don’t fish sink?
– Fish are more dense than water
– Swim Bladders provide enough buoyancy
to offset the animal’s weight
(only found in bony fish)
– The amount of gas in the bladder
changes with depth
Swim Bladder
Gas Exchange:
• How can fish breath underwater?
– Fish take in water (containing Oxygen) in
through their mouth
– Water is pumped past fin gill membranes
(where oxygen is picked up and carbon
dioxide is dropped off)
– Water exits through gill slits
– Circulatory system transports blood
through body
Gills
Osmotic considerations:
Osmotic: The tendency of water to pass through a membrane
into a solution where the solvent concentration is higher, thus
equalizing the concentrations of materials on either side.
• How do they deal with the salinity of
seawater?
– In bony fish special glands in gills excrete
excess salt
– Sharks and rays supplement internal fluids
with urea (occuring in bodily fluids as a
product of protein metabolism)
Defence:
• How can predators be avoided?
– Sight and hearing are usually very well developed
– Lateral line system can detect low-frequency vibrations
– Camouflage:
http://www.youtube.com/watch?v=HSPptPhbFVc
– Countershading
– Schooling behaviour
• *FYI Flying fish can simply disappear by
accelerating rapidly, leaping into the air and
spreading their fins to act like wings!
• http://www.youtube.com/watch?v=gAjzH0vWSIA