Suppose someone captured some fish in the open ocean and took them home to his aquarium (this is not a real-life situation,) would the fish survive if he merely created his own saltwater at home using tap water and the correct ratio of salt, or do the ocean fish need some other minerals or chemicals in their water as well?
(Aside from, of course, food and oxygen)
Well, it’s done all the time. And there are many home aquarium salt formulas you can use to emulate sea water. But they contain much more that salt. Most marine fish sold in the home aquarium trade are live caught in the ocean.
Look up Red Sea Coral Pro salt. That’s what I use.
Oceans are not merely salt water, they are complex chemical and mineral soups. They are also, being extremely large, far more stable chemically, physically, temperature wise, and all other ways, than almost any home aquarium without elaborate feedback systems and monitoring in place. The small critters people keep in marine tanks are tough, shallow-water creatures which can survive the oscillations inherent in artificial tanks.
Regarding what marine fish need. . . probably the biggest thing is space and places to hide. Also, good water circulation. Before getting into it I would recommend studying for at least a couple of months. There are many great forums and articles online about different approaches. You probably want to get some live rock too.
I have a 115 G aquarium with about 150+ lbs of live rock. A 40 G sump. And I have about 10 fish that average about 3-4 inches long.
The fish sold for home aquariums are fish that are capable of living, at least for a while, in a properly maintained home aquarium. If you just pick “a pretty fish” from the ocean, you might get one that is extremely difficult to maintain in a home aquarium. Which is one of the reasons why the early ocean aquariums were located next to the sea, and used circulating sea water.
No longer an aquarium owner. If it was a matter of just tapwater + sea salt = happy fish, I’d probably still be at it. There is constant measuring of pH, salinity and trace element levels, which are in the parts per million.
Marine fish are much more sensitive than freshwater fish. As someone said already, the ocean is a great stabiliser for temperature and water consistency. A river fish, like the tropicals evolved in rivers that could change from muddy as soup to flushed with rainwater, so they are far more tolerant of changed conditions. All they need is water + resin pirate ship + plastic plant to thrive [I simplify, of course].
And, as you will see in the choices available in the salt section of a supermarket, there’s salt, salt and other salt.
They don’t need it, but the freshwater tropicals do a lot better with freshwater salt.
For one thing, tap water may have things in it that are not good for fish. Of course there’s chlorine, but you can let that dissipate by holding the water a few days. But water supplies could have levels of nitrate and phosphate that are not good for fish.
And salt water contains a lot more than NaCl in the way of dissolved chemicals, including trace elements that may be necessary for the health of organisms at very low concentrations.
Thanks for the responses all.
If I may refine my question a bit: Is salt the only truly life-essential mineral for ocean fish survival, and the absence of the other minerals merely means the fish won’t live well, but will still live?
No. It means the fish will die, perhaps slowly enough that you can enjoy watching it do so for some weeks.
By the end of my (freshwater tropical) fish-keeping period, I confined myself to buying fish bred in captivity. They survive much better and you are not depleting wild stocks.
I don’t know if this is changed, but in my era, tropical marine fish were caught by poor fishermen via dynamite – bomb the coral reef pool, pick up the fish which are merely stunned, leave the dead.
Most marine fish being extremely hard to breed in captivity, your choices will be few if you do the ethical thing. Not sure if you care about that, from your question.
The easiest way to maintain the various elements needed is to do frequent water changes. A reverse osmosis filter removes just about everything from tap water, and produces clean water to which an aquarium salt mixture is added.
The Berlin method uses live rock to support bacteria that remove nitrates and nitrites.
Cleanup is also accomplished with a protein skimmer, a device that sends tiny air bubbles through sea water. Waste adheres to the bubbles. A foam is formed that is removed from the skimmer.