Hoplo catfish have better fry survival rates in brackish?!

[knifegill]

So the good 'ol internet ( http://www.sms.si.edu/IRLSpec/Hoploster ... torale.htm ) tells me that hoplo cats are found in fresh and brackish, and in the next breath says that fry survival is much higher in brackish water. I'm not jumping to any conclusions here, that's for sure. Is it possible that the author of the article happened to be spawning cats that originated from brackish conditions? And if so, would hoplo cats from many generations of pure fresh water show no improvement in a brackish set up? I know this is just a fistfull of if's and but's. Let me know all you know about hoplosternum littorale and brackish water, if you'd be so kind. I'm getting a little spun trying to understand. Thanks.

[MatsP]

These fish are very tolerant to different water conditions. As with all "natural selection", variability in the genetics will allow fish to adopt to various conditions - this is why captive bred fish are generally easier to spawn in captivity, for example. In a case where these fish are living in brackish water, the ones that DON'T live well in brackish water will die young, and the ones that are "happy" in those conditions will survive (be "selected"). If you then move them to a soft water condition, they are perhaps not adapted to that.

But it's also possible that the normal habitat for these fish is actually in estuaries or creeks that are brackish - I don't know for sure, but I don't believe they are naturally brackish, but I believe they are very adaptive (and they breed A LOT, within a year and several times during that year, so changes in environment will probably be adopted to quite quickly).

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Mats

[Bas Pels]

If I remember correctly, I think I think I did read somewhere H littorale is restricted to the estuaries.

Wheter this is a reault of needing salt, or failing to compete with a relative which can not survive with salt, further upstream, I could not tell.

[knifegill]

To avoid creating a new thread, I'll ask here. Do they really only live four years? That seems very short for an armored catfish.

[MatsP]

In nature they may well live for an average of 4 years. I'd expect in captivity with no mishaps that they'd live for a fair bit longer - 10+ years. Please note that the page you were referring to is about the species as a introduced/non-native fish in Florida - not an indication of species being kept in aquarium.

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Mats

[Carp37]

Maybe hoplo will see this thread and comment- I'm pretty sure her hoplo littorales aren't bred/raised in brackish water, and I think she started with wild-caught fish. I'm not sure of her fry survival rates compared with other hoplo-type cats (Megalechis/Lepthoplosternum/Callichthys).

[Bas Pels]

I had 2 male Megalichthys thoracum which lived for 13 years after I bought them @ 3 cm.

1 day, the first a month ahead of the other, they just stopped moving, and were dead

[knifegill]

There we go. I was thinking 10 to 15 years would make more sense. Now another for you guys.

A scientific article stub asserts that the only significant spawning trigger for hoplo cats is "a reduction in conductivity". I take this to mean a reduction in salts, electrolytes, minerals, etc. So if my water is already as soft as a pillow, would I gently take them to light brackish and drop them down to fresh again to achieve this decrease in conductivity, or is there a simpler way, say by adding charcoal or something?

[Birger]

There is a pdf on this subject (hoplos) you may like to read

Environmental Biology of Fishes 45: 363-381,1996.
O 1996 Kluwer Academic Publishers. Printed in the Netherlands.
Reproductive seasonality and nest-site differentiation in three closely
related armoured catfishes (Siluriformes: Callichthyidae)
Jan H. Mol
University of Suriname, CELOS, PO. B. 9212, Paramaribo, Suriname
Received 18.1.1995 Accepted 6.6.1995
Key words: Hoplosternum littorale, Hoplosternum thoracatum, Callichthys callichthys, Breeding season, Interspecific
competition, Habitat selection, Resource partitioning, Suriname

Do a search for it or if you can not find it pm me your email address

Birger

[MatsP]

Birger, any chance you could e-mail me that PDF?

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Mats

[MatsP]

Thanks to Birger, I think we have the answer to the "do these fish do well in brackish water". There is a paper by Jan H. Mol (also author of the paper Birger talks about) that discusses the conditions for C. callichthys, M. thoracata and H. littorale.

Basically, the fry grow best in a EC (electrical conductivity) of about 1200-1900 microSiemens/cm, and the fish are not found in really soft water. But the electrical conductivity ranges from around 550-2300 uS/cm naturally in the region. This is not purely salt/brackish water, but "water with relatively high conductivity". And bear in mind that 550 uS/cm is about 550/1.5 ~= 350 ppm TDS - that's similar to my tap-water, and that's definitely not what I'd call "brackish water".

However, the paper does not that H. littorale is not found in the rivers that have really low conductivity (EC 30-80 uS/cm) - so don't keep it in the Discus tank that you have nearly pure RO water in... ;)

Edit:
Source
Mol, J.H. 1994. Effects of salinity on distribution, growth and survival of three neotropical armoured catfishes (Siluriformes - Callichthyidae). J. Fish Biol. 45: 763-776.

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Mats

[MatsP]

So if my water is already as soft as a pillow, would I gently take them to light brackish and drop them down to fresh again to achieve this decrease in conductivity, or is there a simpler way, say by adding charcoal or something?

Just not changing water for a while will raise the conductivity, and doing a large water change (with soft water) would work. I wouldn't add salt to the water. But if your water is REALLY soft (TDS below 50 ppm), I'd say H. littorale isn't the right fish for your water - you'll need to add minerals to the water to make sure the fish is "happy" with the water. The stuff sold in shops for adding to RO water would be suitable, I'd say, compared with marine salt. Just make it up to about 500 ppm TDS, and when you want them to breed, reduce the TDS to about half, then let it rise again to 500 ppm.

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Mats

[knifegill]

Sounds good, but let's say I just use marine salt and crushed coral. Still okay? I've already added some tannins from my blackwater machine and provided them with maple leaves for nesting. On the same vein, these catfish are very hardy and tolerant of adverse conditions, which gets me thinking I could simply stop doing water changes and let the metabolic byproducts accumulate for a while. Perhaps I should remove the water lettuce with its nutrient-exhausting powers and just keep the java moss for now. But where should I draw the line on nitrates for this species? I'm thinking 40-50ppm is a decent level of accumulation while still in the yellow for stress. Thoughts?

I don't have a tool with which to measure total dissolved solids. Since my tap comes out devoid of any buffers or hardness, and I have seen part of the water quality report stating levels of everything are diddly I ought to be somewhat confident that any solids are coming from me, right?

I have added a measly 4 tbsp. of marine salt to their 30-gallon abode just to get them in better conditions. My hygrometer is the cheap floating thermometer kind, but I keep it clean for the most accuracy.

Oh, heck. It's supposed to be a huge, stormy day. I'll get a tarp out there and funnel myself some urban rainwater for later. After the first few minutes of downpour most airborne pollutants will be washed down, right?

And another thing, this pair is rather young and the male's pectoral fins are just beginning to thicken. The female looks egged up, though. So if I try triggering a spawning, will it result in commencement of nest-making, or do I need to wait for him to make a nest before triggering?

[MatsP]

Marine salt is good, I think. Re-checking some of the data in the paper does indicate that "true hardness" is quite low (but still far from "ultra soft" at about 130 ppm in rainy season). In nature, the water is also very low in nitrates, but experience tells us that these fish are tolerant to quite high levels of nitrate - 40-50ppm would be fine, I'd say.

From Jan's e-mail to me:

The paper is good (I think) and shows the distribution of H.littorale restricted to waters with (relatively) high ambient solute concentrations (relatively high conductivity). The term 'salinity' is indeed slightly confusing as the species is not found in saline or brackish waters, but it is also absent in water with extreme low electrolyte content (such as in the interior of Suriname and in much of the Amazon (except white waters). Other callichthyinids can live in these 'distilled' waters. In Suriname these are Callichthys callichthys and Megalechis thoracata. I hope this answers your question.

regards,

Jan Mol

ps A reviewer of my 1994 paper suggested to use the term 'ambient solute concentration' in stead of 'salinity' but I was young then and did not listen to his good advise.

It's also worth noting that to a large extent, it's not very important WHAT the ions/electrolyte is.

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Mats

[Bas Pels]

However, the paper does not that H. littorale is not found in the rivers that have really low conductivity (EC 30-80 uS/cm) - so don't keep it in the Discus tank that you have nearly pure RO water in... ;)

Mats

Dianema however does come from Manaus and so and is therefore very wel suited for a discus tank

They further don't grow as large as H litorale (only half their length) and are a bit less active

So in that case, just go for Dianema

[knifegill]

Good info. I've got rainwater ready, now I've just got to get them fattened up. I also read they should be separated and reintroduced for spawning. True?

[brownhoplo]

In my experience, it simply does not have to do with just R/O or rain water. Although that it is one of many that trigger spawning. We must remember that the H. Littorale that are wild caught are difficult to acclimate and spawn in a tank environment unless the tank is large to mock their natural environment, in addition, they take some time to acclimate to a tank.

Knifegill, where are you located that has brackish waters? What are your goals and how do you plan to "fatten them up"?

[knifegill]

Hello brownhoplo! Good to see a namesake for my interests.

At least two research sources online strongly assert that the only consistent change known to trigger spawning is a reduction in water conductivity, regardless of other parameter shifts. It is this on which I base my attempts here.

My water is not brackish. I'm not sure why you think I do. My tap water has a GH of 62.6. The Ca hardness is only 5.9-12.3 and when degassed, the pH plummets from 7.3+/- down to about 6.6. It used to fall lower, but something has changed down at the water processing facility. I heard they hired a new boss and he tweaked things a bit.

Fattening up, as I've so gracefully deemed it, is consisting of a steady diet of what they condition on in nature. Fly larvae. Of course, the easiest form available is the frozen midgefly variety. They do attack it with gusto. I am also providing them with live blackworm, algae wafers and prepared sinking foods. They really love Cichlid Attack, I suspect it's the vegetable content. EDIT: Add Molly fry to this list. Just moved a gravid female into their tank as a food machine.

Good news is that the one I suspected to be male is ALREADY getting an orange hue to his pectoral leading rays and they are thicker and longer than before, with a slight upward curl at the ends. I was expecting to wait weeks for this, not days. I think it's the marine salt. I've actually seen something of a correlation between superior coloration and health in freshwater fish and the addition of small amounts of marine salt. And I mean trace. As in undetectable by most tests. Yes, yes, it's a no-no for the majority of South American catfish (my favorite continent for catfish), but in the community tank it does wonders (so it would appear without a control group to compare to). Angelfish, longear sunfish, any livebearer (no surprise there) and even my hypoptpomus gulare seem to have better posture when I add a little marine salt. Which I haven't done in some time, since it's a little odd to do so and I do prefer to play by the rules.

I'm relatively sure these are captive-bred specimens, though I have no way to know for sure. They're likely Florida bycatch if not truly captive-bred, knowing my LFS's suppliers.

[knifegill]

Tonight...rainwater! Wish me luck