Osmoregulation in rays (and bull sharks) - need some scientific info

[loconorc]

I posted this in the FW rays forum as well, forgive me if you've already read this. Here is the original post:


Hey all, I'm doing a 12th grade bio project on the osmoregulation of Potamotrygon rays and, if I have time and can fit it in, bull sharks in the Amazon as well. I have a good chunk of my background info planned out, but I am required to have some form of quantitative, numerical data to support my research. I could use any and all of the following, in the form of books, websites, or formal papers:
- Concentrations of urea or the enzyme trimethylamine oxide (TMAO) within the body
- Internal osmotic concentrations vs. the outside environment, or vs. marine elasmobranchs
- Sodium or chloride elimination via rectal glands in marine elasmobranchs or marine bony fish
Any information relating to bull sharks, Atlantic rays, other FW rays, or marine elasmobranchs is very likely still applicable.
Any and all info is welcome and very much appreciated, and thanks!

 

[Jabba954]

PM ZooDiver - he knows bull sharks and rays better than anyone here.

 

[Deano1956]

+1 on Zoodiver, like the average hobiest is going to know that

 

[Zoodiver]

Got your PM and saw both threads. I'll post on this later tonight when I'm not at work. If you search, there are some posts here already that touch on this topic.

 

[Zoodiver]

For bulls specifically, the ability to go between fresh and salt environment has a lot to do with the way they maintain the balance of salt in the body in relation to the levels in the water they swim in. The most promanant way they do this is by controlling the amount of salt they secete in waste/urea. They control the dilution via the renal system (which is why I harp on people about dangers of doing something to jeopardize the renal system, liver and related in captive situations). Screwing up that balance causes they animals to dehydrate (in most cases). And yes, a fish - or in this case shark - can dehydrate while submerged in water. When they lose the ability to control the balance of salt within their body, death is usually the result as their bodies shut down. By manipulation of the levels of salt being secreted via urea, they are regulating the serum levels in their blood. Their bodies are designed to maintain the balance of salt inside the body with what the animal is swimming in. If they are in higher concentrations of salt, the body needs to maintain a higher level of salt (by secreting less). If they move to freshwater, they need to pass more salt to keep the levels lower (by secreting more).

Bulls have a better design in the range of manipulation when being compared to other 'marine' fish.

FW ray info can be drawn for this as well. They pass a lot of salt to keep the serum levels matching the freshwater they are in. Complete opposites of their marine counterparts, which fight to keep salt levels to higher to match the marine environment. One of those topics evolutionists try to avoid. It means things that should in theory be similar went 180* opposite.


Does that make sense?