Shark Catfish Behaviour

[phil335]

Hi everyone,

I'm new to the forum and joined primarily because I understood Neale Monks is a member, I've read his excellent articles about these fish online and subsequently bought his book "Brackish Water Fishes" which is excellent. I'd love to hear the experiences of anyone who is keeping these fish. I read about them, did my homework and waited patiently (about 3 years) until we'd finished decorating/renovating before going ahead and returning to the hobby I'd last enjoyed in the early 70s as a teenager. I've always loved catfish, and having read about the Columbian Shark I knew that was the one for me. So I now have four Shark Catfish in a Fluval 240L tank with a 305 filter, with aeration provided by an old Hy Flo pump (all things 70s are cool!!) I've had the fish for 9 months and they are now between 6-7" and a nice silver colour with erect fins. After discovering the root of high nitrate levels in the tank (my tap water reads 80ppm straight out of the tap) I purchased an RO filter about 6 weeks ago. I've gradually been increasing the salinity since they were purchased and it is now at 1.015. When the fish were young they would flick themselves on the gravel and glass, since the salt levels have increased they have stopped this completely.

Using an API saltwater test kit I consistently get the following readings:

PH: 7.8 Ammonia: 0 Nitrite: 0 Nitrate: 30ppm Temp is 26C.

After the RO filter has done it's work the Nitrate level is 10ppm before I add it to the tank. However I can't seem to get the level below 30ppm in the tank despite frequent water changes. I don't overfeed, 3 times a day and they eat very enthusiastically and quickly. I'm feeding them on Hikari sinking carnivore pellets, Hikari sinking wafers, chopped earthworms, and raw finely chopped beef heart. All of these they consume instantly and heartily. Should I get a nitrate filter to reduce the levels further as I'm wondering if it is stressing the fish?

So what is the problem apart from the nitrate? Well despite seeming very healthy, they spend all of their time up one end of the tank, either sitting together huddled around the filter intake pipe, or swimming up and down the glass. Only when they feed will they swim halfway along the tank, nervously, and returning quickly to the safety of their filter pipe. I have a couple of artificial plants in the tank and a plastic log which they like swimming through at feeding times. I realised early on that the fluorescent tubes that came with the tank were far too bright so I fitted a dimmable, waterproof, colour led strip light to the rear hood, so they have very subtle lighting. I've tried adding various different plants and artificial roots but they seem very sensitive to any kind of change so I've decided it's best to leave the decor as is. I also added a wavemaker at the opposite end of the tank but this just made them huddle together more tightly.

How can I improve their behaviour and help them to become less nervous and shy? We don't have kids, they are in a quite corner of the living room, and we don't make loud noises! Should I add another species of fish to the tank? Would this make them realise that it's "safe" up the other end of the tank? If so which species? I realise they will outgrow their current tank and that I will need to upgrade the tank size when the time is right. However despite reading many articles that state these fish need loads of swimming space, mine don't use the space they've got.

They are stunning fish - perhaps they are quite happy as they are and I'm worrying unnecessarily. So any thoughts,suggestions or other keepers' experiences would be most welcome. Thanks!

 

[thereverendturtle]

Yes adding a dither fish would probably bring them out and about more. Suitable tank mates imo would be monos, archers and sailfin mollies. Most likely, you'll need a quarantine tank where you can get the new fish up to the salinity you have the cats at.
As for the nitrates, a deionizer after the ro unit would take out the remainder. A media reactor with suitable media would work well also. Just depends on which is most economical for you.
Good luck!

 

[nmonks]

I'm new to the forum and joined primarily because I understood Neale Monks is a member,

Indeed, and thanks for your kind words.

So what is the problem apart from the nitrate?

High nitrate levels are common in tanks with predators. Canister filters (especially external canister filters) produce a certain amount of nitrate regardless of the food input because they contain other organisms beyond "good" bacteria. The longer the gaps between cleaning, the more organic gunk collects inside them, and this feeds microbes in the filter media that excrete ammonia, and that in turn produces the nitrate. Some aquarists call canister filters "nitrate factories" because of this effect, and among marine aquarists the switch to live rock was, in part, a response to this. Unlike canister filters, live rock contains both aerobic and anaerobic regions, and that in turn means the aerobic bacteria make nitrate from ammonia but then the anaerobic bacteria turn the nitrate into nitrogen gas. In any case, if your fish are healthy and happy, you may choose to ignore high nitrate levels provided you do the usual weekly water changes. You may also want to use a skimmer (these work above SG 1.010) and have that minimise the amount of nitrate-producing organic matter. Ultimately, in a marine tank (above SG 1.018) you could go the whole hog and use live rock and have a filtration system that manages both ammonia and nitrate in one fell swoop! Ariids look great in FOWLR systems, by the way.

Well despite seeming very healthy, they spend all of their time up one end of the tank, either sitting together huddled around the filter intake pipe, or swimming up and down the glass.

This is very typical for this species. They are migratory fish, and juveniles will swim several, perhaps dozens of miles down the estuary into the sea, and the adults presumably cruise along the shoreline searching for food. In any case, what these fish don't do is spend any great amount of time in one place. It's difficult (impossible?) to provide them with the sort of space they need to feel truly settled, and usually they find the spot with the clearest water current and swim there. Perhaps they feel that's "downstream" and so swimming there feels normal to them?

A bigger tank and/or more powerheads positioned around the tank to add variety to the water flow could both help. Lighting may or may not be a factor. Ariids do seem commonest in murky water, perhaps because their whiskers give them an edge over other saltwater species of similar size and habits. The way they speak to each other through clicking also seems to be an adaptation to living somewhere they can't normally see each other.

Hope this helps, Neale