Which swims faster - saltwater or freshwater fish?  Why?

Hello mel1479~

According to the Australian Museum Fish Site, 
?Most sources believe that the fastest species of fish is the
Indo-Pacific Sailfish Istiophorus platypterus. It has been clocked in
excess of 110 km/h (68 mph) over short periods.? (?What is the fastest
fish?? http://www.amonline.net.au/fishes/faq/fastest.htm )

The Guinness Book of World Record seconds this, saying ?The
cosmopolitan sailfish (Istiophorus platypterus) is considered to be
the fastest species of fish over short distances, although practical
difficulties make measurements extremely difficult to secure. In a
series of speed trials carried out at the Long Key Fishing Camp,
Florida, USA, one cosmopolitan sailfish took out 91 m (300 ft) of line
in three seconds, equivalent to a velocity of 109 km/h (68 mph). By
comparison, the cheetah, the fastest land mammal over short distances,
can reach top speeds of around 96.5 km/h (60 mph).? (?Fastest Fish:?
http://www.guinnessworldrecords.com/content_pages/record.asp?recordid=51366
)

The Istiophorus platypterus is a saltwater fish, found in the Atlantic
and Pacific oceans

Partly because it's so fast (and partly because of the fish's
migration habits), science doesn?t know a great deal about this fish.
It's currently unknown how they can swim so fast. Nonetheless, the
fish?s long, sleek body, beginning with a needle-shaped mouth, with
dorsal fins running the length of the fish?s body, must have something
to do with its ability for speed.

For several excellent pictures of Istiophorus platypterus, and more
information on the habits of this fish, see ?Sailfish? at The Florida
Museum of Natural History:
http://www.flmnh.ufl.edu/fish/Gallery/Descript/Sailfish/Sailfish.html

Regards,
Kriswrite

RESEARCH STRATEGY:
fastest fish
"Istiophorus platypterus"

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Request for Answer Clarification by mel1479-ga on 11 Oct 2004 09:36 PDT

What I need to know is: does water with salt or freshwater (in
general) effect how fast a fish swims?  For example, does the salt in
the water make a fish more boyant and thus swim faster than a
freshwater fish or vice versa?

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Clarification of Answer by kriswrite-ga on 11 Oct 2004 10:33 PDT

Hi Mel1479~

This is quite a different question from your original one, but to be
friendly, I have emailed a few marine biologists with your question.
Hopefully, they will answer soon.

Kriswrite

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Clarification of Answer by kriswrite-ga on 11 Oct 2004 12:37 PDT

Hi again Mel1479~

Well, the experts at The Oregon Coast Aquarium wrote back promptly. :)
Here was their reply:

"Some saltwater fish swim faster than freshwater fish, but it has
nothing to do with salt in the water. Saltwater is in fact more
buoyant than freshwater, but almost all fish have a swim bladder to
control their buoyancy; therefore, making buoyancy easily achieved by
any fish salt or fresh. What saltwater fish have to overcome is a
difference in the density and viscosity of the water. Because
saltwater is more dense and viscous than freshwater, it is probably
more challenging (for a fish) to swim through saltwater than
freshwater. But why then do many saltwater fish swim much faster than
the fastest freshwater fish? The answer lies in the habitat. Saltwater
fish are dealing with a much larger and less restrictive habitat than
freshwater fish. This is also why many saltwater fish get much larger
than the biggest freshwater fish."

Kriswrite

With all due respect: Your original question has been answered
perfectly. If you desire to learn more, may I recommend that you post
a second question?

Regards,
Scriptor

Kris, what a great answer, and the extra effort your gave Mel is
inspiring for all Researchers.  :)

Best regards,
journalist-ga

P.S. Mel, thanks for asking this great question!