Freshwater Tanks

[LFS42]

That's why I advocate that you don't support those stores.
Even if they have the best prices in town, you can't reward bad behavior.
If they sell an Oscar to a 12 year old for a 10 gal. w/goldfish, what will they tell you about that bluespot jawfish that hasn't eaten in a week.

 

[Anonymous]

Seamaiden,
FYI, all cichlids are SECONDARY DIVISION freshwater fishes. Meaning, they are all derived from marine fishes. Primary division freshwater fishes were ALWAYS freshwater fishes. If the rift valley cichlids had come from different origins as the rest of the cichlids - they wouldn't be cichlids anymore, if you follow me. :wink:
Jim

i think i do...but...wouldn't, then, all fishes once have been salties (before the advent of land)?

please tell more! seein' as how i'm a simple autodidact i choose my own readin' and surely have missed out on some basics, or maybe some advanced basics?

mongo, you've lost me now...help? oh, wait! that's what an edumacation is for! all salties derived from fresh? did i get that right?

 

[mongo]

mongo, you've lost me now...help? oh, wait! that's what an edumacation is for! all salties derived from fresh? did i get that right?

All marine teleost fish (bony fish, not the sharks etc) are derived from freshwater ones. The best evidence for this is that the osmolality (salinity) of the body fluids for marine teleosts is the same as it is for freshwater ones. This means marine teleost fish are hypoosmotic (less salty than the surroundig water) and getting rid of metabolic waste is energetically demaning (pumping ions up a concentration gradient) so ammonia and nitrate in the water is highly toxic - makes it even more difficult for fish to get rid of waste. Freshwater teleost fish are hyperosmotic (more salty than surrounding water) meaning getting rid of metabolic waste is easy (pump ions down a concentration gradient). This is a major reason why freshwater teleosts are so much more tolerant of ammonia, nitrite and nitrate in aquarium water.
Hope that made sense... :lol:

 

[Anonymous]

Furthermore...the marine origin of cichlids is the reason why they are so tolerant of salt in their water, and not just he rift lake cichlids either.
Jim

 

[wombat1]

Mongo,
So did sharks, lampreys, and hagfishes all derive from marine ancestors? What about sturgeon, aren't they sort of a mix of teleost and sharklike traits? I'm sure this is all based on sound genetic evidence, but one thing confuses me. Why couldn't it be the other way around, marine fish evolved to FW and kept the same osmolality? How does the similar osmolality of the two groups tell you which direction evolution went?

 

[mongo]

Mongo,
So did sharks, lampreys, and hagfishes all derive from marine ancestors?

Yep. The hagfish is the "original" fish with fossils around 500 million years old. Interestingly these are osmoconformers (they change their osmotic levels to match the environment). The sharks are almost all marine with very few ever known to be freshwater (there are some freshwater rays).

What about sturgeon, aren't they sort of a mix of teleost and sharklike traits?

Yep, they are closely related to the sharks but still not technically a teleost.

I'm sure this is all based on sound genetic evidence, but one thing confuses me. Why couldn't it be the other way around, marine fish evolved to FW and kept the same osmolality? How does the similar osmolality of the two groups tell you which direction evolution went?

You could argue it did go the other way, the evidence is genetic, fossil and geographic. The osmolality by itself might not tell you which way it went, but you have: 1) most of the oldest teleost fossils com from freshwater habitats. The oldest marine teleost fossil is much more recent tham the oldest freshwater teleost fossil. 2) most of the existing old teleost groups are also almost exclusively freshwater (minnows, tetras, catfish, bonytongues). You also know these groups have always been freshwater because they are geographically constrained, for example - no tetras in north america, europe or Austrailia (I think) and no minnows in south america. If they had been marine at some point you would assume a more global distribution for these groups becuase they or their ancestors could migrate along coasts... I love this stuff, pathetic isn't it?

 

[wombat1]

That's the kind of evidence I was looking for, thanks. I wouldn't say pathetic, just knowing everything about one thing rather than knowing one thing about everything.

I just learned that about hagfish this week, very interesting.

This is a major reason why freshwater teleosts are so much more tolerant of ammonia, nitrite and nitrate in aquarium water.

Another reason is the shift in equilibrium towards NH4+ (nontoxic ammonium) rather than NH3 (toxic ammonia) at the lower pH of a FW tank.