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Cat
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Reged: 09/15/03
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River dolphin physiology information
      #131571 - 12/02/05 02:20 PM

I am doing a presentation on the Baiji, and I wanted to discuss the physiological differences between marine dolphins and freshwater dolphins. However, there doesn't seem to be a tremendous amount of information on river dolphin renal systems which is what I really wanted to focus on.

I know that marine dolphins have extremely large kidney with a lot of lobes; but what about river dolphins? They don't drink the water they live in as far as I can tell, so would they pretty much have the same largeish kidney?

Also, what about river dolphin skin and how it differs from marine dolphins?

Thanks guys!!

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KasatkaAdministrator
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Re: River dolphin physiology information [Re: Cat]
      #131572 - 12/02/05 10:30 PM

I've been trying to find out about their skin for years (at least four or five) and haven't come up with anything. =\

Here's some interesting info from my shiny new book though:

- Amazon River dolphins are the only living cetacean with differentiated dentation. (The teeth in the front half of the jaw are conical, and the back half are more like molars, but not quite.)
- Platanista lacks a functional eye lens and only can determine degrees of light and dark
- There's been a split of river dolphins into two families. The baiji would be in Iniidae with the Amazon River dolphin and the La Plata River dolphin
- Iniidae are considered more related to the other oceanic dolphins and porpoises than the Platanistidae family because of a vestibular sac along the nasal passages and the reduction of the attachment of the ear bones to the skull.

I'm going to look around some more. I found little bits on things like the gastrointestinal tract (nothing significant so far, but I'll read more when I'm more awake). I have an article on marine mammals drinking seawater and the rates they're able to excrete stuff, but nothing relating to river dolphins. I don't see why they wouldn't if they needed to, and if it was freshwater, perhaps it would be smaller.

I asked the Navy about river dolphin skin, and they never got back to me. I asked a trainer I know about it once, like... why freshwater makes marine dolphin shed so much, and how do river dolphins cope, and he said they shed like crazy too, but I don't know anything more than that.

Maybe contact a park that had someriver dolphins? Shedd, Sea World, Marineland Florida, Pittsburgh Zoo... though since most of those places held them eons ago, they might not have much info.

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~ Kim


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Klondike
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Reged: 08/09/04
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Re: River dolphin physiology information [Re: Cat]
      #131573 - 12/03/05 04:07 AM

Since it is supposed that they are only secondary freshwater species, their kidneys might be large but probably still on the way of reducing.
I think osmotic pressure and diffusion hold important roles (water "wants" to go where there is an higher solution of molecules -> freshwater "wants" to get into a River dolphins body).
Also, from my experience, their skin is definitely different (at least of the Amazon River dolphins) from the one of Belugas, Orcas or Bottlenose Dolphins, thicker and without those skin grooves, but still smooth and on the beak quite hairy (robust bristles, even a little scratchy).


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Cat
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Re: River dolphin physiology information [Re: Klondike]
      #131574 - 12/03/05 06:00 AM

Wow, excellent info guys, I really appreciate it!!!

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Klondike
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Re: River dolphin physiology information [Re: Cat]
      #131575 - 12/03/05 09:22 AM

You are welcome!
Besides, a befriended keeper, who has worked with Botos since 30 years, is pretty sure that they drink freshwater.


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Cat
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Re: River dolphin physiology information [Re: Klondike]
      #131576 - 12/03/05 01:47 PM

Really? Well I will take your word on that since there is really no definitive way to tell if botos drink it in the wild. I wonder if Baijis drink the water even though it is heavily sedimented.

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Klondike
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Re: River dolphin physiology information [Re: Cat]
      #131580 - 12/04/05 03:15 AM

That's what he said...and he is presumably the only one on this planet who has 30 years of Boto-experience, and counting!
Of course you can't really proof it and maybe wild ones don't do it...i guess we will never know. Unfortunately.
What is your presentation about? The Baiji as an extinct species?


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Cat
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Re: River dolphin physiology information [Re: Klondike]
      #131581 - 12/04/05 06:06 AM

Yes, it's about the baiji as an extinct species. It's really not a big presentation, but it is supposed to focus on conservation, and I thought it would be important to let people know that a large mammal that most people don't know about is going to be gone in a matter of years.

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fintrainer
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Re: River dolphin physiology information [Re: Cat]
      #131587 - 12/05/05 09:47 AM

In terms of "drinking"...
Oceanic dolphins don't "drink", they get all their fresh water through their fish that they eat. I would imagine that would hold true for River dolphins as well, creating little differences. Whether even eating freshwater or saltwater species of fish, I *believe* the water stored in the body is they same, therefore, little difference to the animals eating it. I know we prefer feeding natural species, but many facilities have also fed captive cetaceans and pinnipeds freshwater species, such as Lake Trout, with no apparent drawbacks.


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Klondike
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Re: River dolphin physiology information [Re: fintrainer]
      #131588 - 12/05/05 11:43 AM

Yes, everything you say is true.
But you forget that oceanic dolphins just don't drink water because absorbing even more salt actually means harm to them as mammals are not adapted to drink sea water.
Freshwater, on the other hand, doesn't represent any danger, it can only help (and we all know about especially older dolphin's kidney problems).
Besides, I am sure dolphins can distinguish between salt- and freshwater easily and maybe their love for ice-cubes isn't just because of the prickling feeling.
Wild belugas have also been seen nibbling on floes.


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