Salt Tolerance

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ishmael9913

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Nov 5, 2003
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Hello all...
Im not sure if this is the correct forum to place my inquiry in, but it will have to do. I am a student working in an aqauculture class. I am currently running a 440 gallon recirculating freshwater system. I have tilapia in it, and my temperature is around 78-80 degrees F. My research that i am hoping to study is the tolerance of Tilapia to salt water. I intend to increase salt levels slowly so as to let the fish acclimate to the salinity. What i am wondering is whether or not anyone knows the effect of salt poisoning on freshwater fish. I need to know what signs i am looking for that says that i have too much salt in my system so i dont kill my fish.
Since at some point i will have brackish water, i thought this would be the forum to post it under. Any help anybody could give would be much appreciated.

Thanks again,
Keaton
 
I would think that they'd be able to tolerate a specific gravity of about 1.005 at the most. Anything higher you'd be minus a bunch of tilapia. The salt concentration will get too high for them and burn their skin and scales.
 
Saltwater doesn't really poison freshwater fish--it irritates their gills and mucus coating in short term shock exposure, often causing the fish to twitch and flash. With slow acclimation, you probably will not see any serious signs of intolerance, externally. True freshwater fish will eventually die because their kidneys will fail as they are overwhelmed with the salts. The fish basically cannot remove the salt from it's blood, and can not regulate the osmotic balance of water outside and inside it's cells.

Tilapia, however, are brackish/fresh water fish and are cultured in hypersaline conditions, so they are quite able to process the salts safely. They can tolerate full marine conditions, if acclimated slowly.
 
Thanks guys!
Although your points of view seem to conflict a bit, so who is right? ;) I agree that Tilapia are a very resiliant fish to other conditions and it would make sense they could process salt water conditions as well. I just really think it would be great to have a salt water system with Tilapia in it. So the fish will flash and twitch then if i put too much salt in too fast? Any other problems i might with a saltwater system? I have only worked with freshwater before. I know that any metal parts are bad because they introduce trace metals into your system through the salt water. Does salt water have any effect on the biofilter? Does the bacteria grow differently in salt water...or a different bacteria...or what? Any help would again be great!
 
I'd say oriongirl is right, she's one to take seriously when dealing with the more scientific side of aquariums =)
Oriongirl: what did you take in school? Did you go to post sec. ?
 
The nitrification bacteria responsible for oxidizing metabolites in FW are considered to be different from those for SW. Where in the density scale the change-over occurs is unknown to me.
 
Metal parts are bad in SW systems more because they begin rusting, and soon have to be replaced. With the exception of copper, most metals don't have much impact, since it's not like the metal dissolves--the flakes are not really harmful. Copper is deadly to inverts, but even it is found in small amounts in the ocean (much smaller than hobbyist test kits can detect).

As RTR said, there isn't a whole lot that's known about the difference between the FW and SW bacteria. At least one member here converted a tank to SW without noting any spikes in ammonia or nitrites--but who knows what that really means. In many cases, a gradual shift to SW does not result in any apparent problems for the biofilter, but this could be due to the increase in salt tolerant bacteria as the salt intolerant ones die off.

cdawson-- shockingly, no. All my formal education has revolved around computer hardware, software and business management. Since I build and maintain databases for fisheries biologists and culturists, I've had to learn quite a bit about their jobs in order to do mine better. My boss had tilapia when he first moved to the state, and he talks about them quite a lot. Some of the culture techniques used are similar for tilapia and trout (we mostly raise trout), and there's a ton of scientific studies on tilapia--you can't read anything on commercial aquaculture without reading about tilapia. Salt is used for treating a variety of trout issues--fungus, minor injuries, parasites. The hatchery guys just dump 2-3 bags of rock salt at the top of the raceways. The trout never really show much reaction--a bit more active than normally, a few shimmies. The specific gravity jumps as high as 1.029--well above marine conditions--but it doesn't seem to cause any long term problems for the trout, and remarkably few deaths (1-2 for 5,000 fish).
 
Thanks for all the help guys. I think i have some metal fittings that go from my pump into my biofilter, but we will see what happens. Im pretty sure they arent copper so we shouldnt have a problem. I will continue to post on what happens. I do have one other slight issue. It seems as though my bio-filter hasnt kicked in yet. I know that it takes some time for the Ammonia levels to get high enough for the bacteria to kick into gear, but when i had my tank before it cleaned up much faster. I have ten tilapia in the tank right now and man it is very cloudy. Any tips on biofiltration would be great!
 
BioSpira is about the only commercial product I will recommend, as it does seem to work.

If you have an established tank, swap some of the media into this tank. You're probably running bare bottom, but if not, a bucket of media from an established tank will help as well.


Keep the ammonia levels low--below 1 ppm ideally. The bacteria will develop as long as there is any detectable ammonia--lots or a little. The bacteria grow--they don't care if the larder is full or not. High ammonia will burn gills, even on hardy fish like tilapia.
 
I agree that high ammonia levels will kill the Tilapia, mine are definetly not that high yet. What is this commercial bio-filter media you speak of? We are in high school, so most of our stuff is kind of retrofitted junk systems...lol they do have their own personalities though. Which is kind of cool. For our biofilter media we use soda pop rings in large quantites. Oddly enough this seems to work great for all systems we have built so far. Obviously the surface area is not as great as some other products. Any ideas for a better material short of buying some?
 
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