brackish aquarium?

Question
QUESTION: I went to a walmart yesterday looking for small fish for a freshwater aquarium. I purchased 2 blue-three-spotted gouramis that are less then 2 inches long, 2 guppies and a 3 inch blackfin shark. I was told these would live well together and stay small. Upon doing some research, I found that the blackfin shark (columbian shark) would grow possibly to 1-2 feet long! I also found out that it needs brackish water (even though it is old as a freshwater fish). I only have a 10 gallon tank right now, and Realize that I am going to need to upgrade my tank size soon (I thought these fish stayed smaller and would be ok according to the 1 inch per gallon rule, I didnt want to over-crowd my tank). I expect that the guppies might get eaten by the gouramis or the shark. I am wondering WHEN I will have to start adding salt to the sharks water (I have never had a brackish or salt aquarium before) I want to keep him healthy and happy. I also read mixed information that the gouramis CAN live in low salt brackish water and live with the shark as this particular breed of gouramis become agressive when they get bigger. Is this true (I dont want to kill my fish!)? I am having such a hard time finding information on this. If I keep only the one shark and 2 gouramis together, what size tank will I need? Money and space is kind of a factor (I read some people bought 200 gallon tanks, I just cant do that). This is my first tank in the last 6 years, it seems a little more then I was expecting for care and maintenance, but I am determined to succeed (and glad I did some research on my own, as the store was no help). I also wanted to have a salt water tank someday but it seemed like a difficult thing to undertake, but I think upgrading to brackish water will be a good medium to learn how to care for salt water fish. I also read that as an adult my shark can be in a full salt tank if I choose (though I am sure the gouramis wouldnt tolerate it). I am a little upset that the store didnt have accurate information on these fish, as I wasnt planning on buying a larger tank. Thanks so much for your help and I hope you can fill me in on some answers. Thanks again.

ANSWER: Hi Rachele,
Duped by a pet store... you aren't alone there. I'm sorry. Pet store employees are never the most informed or educated people(though they should be#. Hexanematichthys Seemanni, the Blackfin Shark or Columbian Shark is a hard one to keep. They usually get lumped in with the freshwater fish species but this fish is not purely a freshwater fish. It is actually a brackish water species as juveniles that will slowly need to be acclimated to a full saltwater tank as they get bigger. The potential adult size of this fish is also often misrepresented. They can reach 20 inches #51 cm# or more in size if taken care of properly. They are extremely active swimmers. Hence the need for space. Colombian Sharks also have venomous dorsal spines#similar to a Pterois Volitans, Lionfish#, so be very careful when performing your tank maintenance. It's probably a really good idea to get some long rubber aquarium gloves. It's nothing fatal but can cause a sting similar to that of a wasp and be extremely painful. Being catfish, they are primarily scavengers. They will constantly be looking for bits and pieces on the bottom of the tank. Give them sinking shrimp pellets, catfish pellets, prepared sinking foods and supplement with live or frozen foods such as blood worms, mysis shrimp and even krill. As they get larger they will eat anything that fits in their mouth. Even the 3 Spot Gouramis, that can reach 6 inches, could quite possibly become food. A specific gravity of 1.005 to 1.010 is ideal for their brackish environment. Increasing as they grow to full marine at 1.024 to 1.025.
Trichogaster Trichopterus, The Three-Spot Gourami, like all the variants of this species, are generally considered good community fish when small but they are not as peaceful as the other gouramis. They have been known to attack smaller fish. They can also get belligerent or territorial when they get large#5 to 6 inches). This species group is certainly one of the hardiest available to the aquarist, and makes an excellent first fish for new aquarists or returning aquarists. They are long lived fish with each having a remarkably individual personality. They will use their pelvic fins to feel their environment and even feel their tank mates. They also seem to be quite aware of their owners. I've seen some that actually desire contact at feeding times. As far as the brackish environment goes, it is not their optimal environment. They will tolerate that salinity but not thrive in it and it can shorten their normally long lives. Three-Spot Gouramis are found in marshes, swamps, and canals. They inhabit shallow sluggish or standing-water with a lot of aquatic vegetation in seasonally flooded forests throughout the middle and lower Mekong. They undertake lateral migrations from the Mekong mainstream, or other permanent water bodies, to flooded areas during the flood season and return to the permanent water bodies at the onset of the dry season. They primarily feed on zooplankton, crustaceans and insect larvae but also vegetation. They are omnivores so they need a varied diet, and take to dried and dehydrated combinations easily.
Now the hard part. The size of your aquarium is way too small and the fish will eventually need to be in separate systems, you can get by for a few months but you will need at least 75 gallons, full marine, minimum for the Columbian Shark eventually. A 30 gallon will be the minimum size for your Gouramis. You can get by with a 55 gallon for a year or two as a brackish environment. But they will outgrow that by that time.  Saltwater is not necessarily harder to maintain than freshwater environments. You just need a bit more patience when setting it up and cycling. Making sure salinity, Ph and alkalinity is optimal. My systems that have been in place for 2 years and longer require very little maintenance compared to my freshwater systems. You should familiarize yourself with Craigslist. I have purchased many large systems there at next to free prices. If you have any more questions ask away.


---------- FOLLOW-UP ----------

QUESTION: Thanks so much for that info. So I should get a 75 gallon for the shark and a 30 gallon for the Gouramis... Do you think they can live in this smaller tank until october (the gouramis are about 1.5 inches and the shark is 2.5-3inches right now)? I am moving in october and would be happy to set up their bigger tanks once I am moved (if not, maybe I will put them all in a 30 gallon tank until I move and set up the big tank after).
I will have to check craigs list. I used to have 2 55 gallon tanks but my mother sold them when I was away at college. I do hope that my shark doesnt get TOO big.

My follow up question though, is can I have other fish in with the shark in a 75 gallon tank? What kinds?

How about the gouramis when they are in a 30 gallon tank? Can they have tankmates?

This is not what I was planning when I went to the petstore. I wish the employees were better informed. I just bought a 10 gallon aquarium 2 days ago thinking I would just set up a few little fish, now I have to buy all these other tanks too! (Sorry, I know this happens with petstores all the time, they didnt even know what kind of gouramis they were, I had to find that out myself).

Im sure I will have a lot more questions for you, thank you for answering so quickly!

Answer
Hey Rachele,
You should be ok til October, then you can get the larger tanks. The sooner the better but you can make do with what you have for 2 to 2 and a half months. Then I would get a 75 and a 29-30 gallon. Just be sure to check water quality and do weekly changes after you have cycled completely. You should start adding the salt now. Mix it in a separate container with aquarium water. Measure with a hydrometer or refractometer to 1.005 and gradually bring the tanks salinity up to 1.005 over the course of 2 to 3 weeks. Tank mates should be fine with either species as long as you use the "fits in their mouth" rule. Nothing that fits in their mouth is a good idea. Just pick tank mates that are similar in size. The Columbian Sharks will eventually be able to have a HUGE variety of tankmates to choose from! Literally an ocean to choose from.  Good luck and let me know how it goes or if I can help more!