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Before you read this I want to let everyone know that I have read the brackish water articles/faqs and around 20 or more profiles on Columbian Sharks. I need a little more personal experience now.

Hello everyone. I have been searching the net for quite some time trying to wade through all of the opinions, suggestions and alleged facts about Columbian Sharks. I am one of those people who research things to death before I make up my mind. This would be one of those times that I did not do that. I saw the fish and fell in love. Now I need some real information from someone who has successfully kept these fish for a length of time. By the way I am not new to fishkeeping, just keeping these fish.
I purchased three Columbian Sharks (two inches each) and they are in a 75 gallon. After a lot of research I've learned they are brackish water fish and I've done a lot of reading on that. I purchased marine salt but have not yet purchased a hydrometer or a refractometer. That's just one of my questions. So, without further ado, here are some of my questions.

1)Is a hydrometer or a refractometer better? Which one is easiest to use and understand? I want the best, easiest one. I know there is a big cost difference but that is not what is most important to me. I really need something that is easy and accurate.
Not being a scientist at all I'm a bit concerned about getting the salt content where it is supposed to be.

2)What size tank will I need in the long run for the three of them?

3)What should I feed them to keep them on a varied diet?

4)What other important information can you give me about them? Anything and everything you tell me will help me be a better mom.

I'm sorry for writing so much but my husband said I had to find
someone who was knowledgeable and stop trying to muddle my way through all of the information on the net.
I appreciate all the help and guidance you can give me.
Thanks, Bridget
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Bridget, Welcome to Planet Catfish...

N. B. I haven't kept this fish myself, but it's been written about in the forum several times. Here's my take on a conclusion.

1) Either will do fine for what you want to do. The refractometer is definitely the more accurate (and expensive) solution, but as you only need to be reasonably accurate with respect to the absolute salinity (you're not aiming to get exactly 1.035 specific gravity for example) as the species is tolerant of a wider range than your average tropical marine fish.

However, you do want to keep it "the same" once you've reached your final salinity level (say 1.020 - but that's just some number I made up, not a recommendation to aim for that number), you want to make sure the water you add is the same salinity as the tank and not increasing or decreasing every time you add/replace water.

2) As they grow past 300mm, your tank for fully grown fish should be at least 1200 x 600 x 600 mm (or 4 x 2 x 2 foot if you prefer imperial measures). That's about 450liter, 125 US gallon or 100 UK gallon.

3) Whilst the article I wrote is aimed at pleco's, you can get some ideas by following the link at the bottom of this post - any "omnivore" or "carnivore" food would work well with this fish from what I've read. You are probably best off combining some "natural" food with prepared food (such as flakes or granules intended as "general fish-food").

4) No further info from me.

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Mats

Thanks for the information. It was very helpful. I appreciate you taking the time to help me out.
Bridget

One thing i would like to add is that it is not essential to add water that is of the same SG as the water in the tank when adding new water. Brackish enviroments are constantly changing as the tides go in and out and as such brackish fish such as the shark cats are perfectly designed to deal with these changes. As long as you are within a ball park figure of the SG of the tank all will be fine provided it doesnt alter the tank SG by more than 0.003 or so either way, although the fish will easily handle a change larger than this the filter bacteria may not.

The SG figure you want to be aiming for is between 1.010 and 1.018 , of course you can go higher to 1.022 as the fish is fully adaptable to marine water but there is really no need.

You shouldnt have any problems with feeding them, from my experience these fish will eat practically anything you offer them.

Be prepared to be amazed at how much salt it takes to reach 1.010, you can expect to use about 5 kilograms of salt in a 75 gallon tank. Dont bring the SG straight up to 1.010, add salt dissolved in water daily not changing the SG in the tank by more than 0.003 each day as to not shock the filter bacteria

i have kept 4 Columbian Sharks in a 'faux' salt 125g (i.e., nice white sand, brackish conditions). they will grow rather steadily as they have very hardy appetites. as previously stated, they're not terribly picky. i fed a mix of frozen bloodworms, krill, pellets, and (eventually) cuts of whiting, catfish nugget and other cheap cuts from the local grocer. don't be alarmed! i did this primarily because some of the other fish i was keeping were eating me out of house and home.
DO TAKE NOTICE:
since these fish are brackish and, in the wild, make annual migratory journeys (much like birds) to spawn, you will observe them growing increasingly restless as they reach 5-7 inches. one assumes this is due to the 'call of the wild'. varying temperature and salinity may help calm them down.
These are certainly wonderful creatures. Itâ??s a shame that one often sees juveniles in the hobby, but rarely good sized adults. I wish more people had such a dedication to the animals they keep such as you have shown. Enjoy your Columbians! â?¦and keep us updated

There's multiple likely reasons for not seeing more mature fish in the shops:
1. Bigger fish -> more waste -> need bigger bags to transport well -> much more expensive to ship. [1]
2. The larger fish are in a marine environment -> not easy to catch.

There's also side-effects of the size:
1. Bigger fish -> bigger price -> harder to sell due to price
2. Bigger fish -> need bigger tank -> harder to sell because many people don't have larger than 55g/200 liter tanks. An adult 300mm/1ft fish will not be that easy to sell to someone with a small-ish tank.

[1] If you double the size of the fish (length-wise), you also get roughly double the height and width, which means that it's most likely going to weigh about 8 times more - and thus produce roughly 8 times more ammonia for the same shipment. So a double-the-size fish should really cost 8 times more - they don't, because the shop/importer/exporter takes a hit on selling the bigger fish (for the benefit of "getting more money in one go").

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Mats

While I donâ??t disagree that a bigger fish costs more to ship; eight times more? Hardly. Shipping is based on weight. The major weight factor in fish shipments is the water. An 8â?

The quantity of water that you need to ship a certain size fish is related to the amount of ammonia the fish produces, which I'd say is directly related to it's mass (assuming of course there's sufficient air-supply that the fish doesn't asphyxiate before it's been ammonia poisoned - but air isn't generally causing a problem in fish-shipping, as far as I understand [1]).

Of course, if you're only shipping one or two fish, you'll probably put more water than necessary in the bag "just to be safe". But if you're a wholesaler that ships several shipments every day, you'll need to think about how much water you put in each bag, and how many fish you can get in the bag with a certain volume of water (i.e. weight).

If you can put 8 4" fish in a bag, or one 8" fish, which would you put there?

And just to confirm, it's quite clear that if you double the lenght, width and height of any particular geometric shape, you will definitely get 2 * 2 * 2 -> 8 times more volume, no matter what shape it happens to be. Fish weight is pretty linearly related to it's volume, so 8 times more volume gives 8 times more weight.

[1]Shipping is done on a combination of weight and parcel size where the shipper usually pays "whichever is highest", but sometimes its combined weight and volume. Clearly, shipping an emtpy box of one cubic meter isn't based on it's weight!

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Mats

MatsP wrote:The quantity of water that you need to ship a certain size fish is related to the amount of ammonia the fish produces,

Agreed, ammonia is a concern during the shipping process. Still, large fishes are successfully shipped all the time.

â?¦which I'd say is directly related to it's mass (assuming of course there's sufficient air-supply that the fish doesn't asphyxiate before it's been ammonia poisoned - but air isn't generally causing a problem in fish-shipping, as far as I understand [1]).

I canâ??t say I agree for 2 reasons:
1) While I do agree that the larger the fish, the more ammonia it produces (and so, one could argue that since ammonia production is related to size it is also related to mass since mass=density*volume, i.e. size); I donâ??t know that it is a direct 1:1 ratio, mass:waste. To my knowledge, shippers qualify fish in terms of length, not mass. So, if a 4â?

deepblue wrote:

MatsP wrote:The quantity of water that you need to ship a certain size fish is related to the amount of ammonia the fish produces,

Agreed, ammonia is a concern during the shipping process. Still, large fishes are successfully shipped all the time.

â?¦which I'd say is directly related to it's mass (assuming of course there's sufficient air-supply that the fish doesn't asphyxiate before it's been ammonia poisoned - but air isn't generally causing a problem in fish-shipping, as far as I understand [1]).

I canâ??t say I agree for 2 reasons:
1) While I do agree that the larger the fish, the more ammonia it produces (and so, one could argue that since ammonia production is related to size it is also related to mass since mass=density*volume, i.e. size); I donâ??t know that it is a direct 1:1 ratio, mass:waste. To my knowledge, shippers qualify fish in terms of length, not mass. So, if a 4â?

Good point. I have heard of fish coming in with ammonia burns. However, none of the fish I've ever received have had any problems. An 8â?

I agree. There are plenty of species that grow fairly large that are often available as "returns" in shops, whilst others almost never appear, although they should grow to equal or larger size. I think you hit the head on the nail as to why: They don't receive proper care.

The most common large species is of course common plecos, and they are pretty much bullet-proof, so that's probably why.

Oscar's and other larger cichlids are also more likely to survive, as they will kill anything smaller in the tank, and thus become "winners" in the contest of growing in a reasonably clean tank.

The Colombian sharks have an additional complication that they will prefer a brackish to marine environment, which isn't what most people who buy from ignorance will give them - many shops that sell them probably don't even know that they need brackish water...

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Mats