Corydoras Pygmaeus Sensitivity

[jar]

Has anyone here experienced very sensitive pygmaeus?

I have very sadly had two batches from two different shops in melbourne. The tanks they were in had pretty good water parameters 0.1/0/0 Ammonia/Nitrite/Niterate (There was only a slight trace of ammonia, almost undetectable).

I am beginning to thing it may be a water hardness or pH thing.

[MatsP]

No nitrate and low levels of ammonia indicates that your filter bacteria are somehow not working as they should... [Or your test kit isn't working as it should].

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Mats

[jar]

Yea, i was resorted to a few large water changes after the first few died, so not surprised there were no nitrates. The ammonia was probably just detectable because there had been some dead fish in the water.

[MatsP]

And you do not have ANY nitrate in your tap-water? Lucky you.

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Mats

[Mike_Noren]

For what it's worth: Yeah, I've found Corydoras pygmaeus to be an extremely sensitive species. On both occasions I've kept it I suffered almost 50% casualties within a month of purchase, for no apparent reason and without the fish displaying any clear symptoms. They'd just keel over and die one by one. Only two individuals (out of a total of 30) are still alive, two years after purchase. Personally I'd rate C. pygmaeus as about as sensitive as Aspidoras pauciradiatus, and infinitely more sensitive than C. schultzei, C. aeneus, or C. paleatus.

[jar]

My tap water doesn't have nitrates that i can detect anyway. Is it that common?

Im glad to know that I am not the only one. I am going to pick up some more, and am going to have to dedicate a lot of extra TLC to get them through the transition!

[MatsP]

My tap water doesn't have nitrates that i can detect anyway. Is it that common?

It is in the UK, that's for sure. Obviously, this differs a bit from region to region within a country, and certainly from country to country, as the water comes from different sources, that have different levels of "natural" nitrate [the nitrate may actually come from fertilizers that farmers put on their fields, etc].

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Mats

[Mike_Noren]

Some nitrate is normal yes, but ignore the nitrate reading, it's nearly non-toxic and not the source of the pygmaeus deaths.
Ammonia is very toxic and may kill sensitive fish in concentrations as low as 1 ppm.
However, what did you use to test the water?
If you used any kind of plastic stick, strip, or paper, you can, in fact should, ignore all the readings - they're so horribly inaccurate that one's much better off simply looking at the fish. If you used a drip test or an electronic meter, then the presence of ammonia and absence of nitrate does indicate that the aquarium has not yet matured, and that it's too early to add sensitive fish.

Would you happen to know the origin of your fish?
I suspected the reason my pygmaeus were so sensitive was because they were czech-bred, and I've had so many bad experiences with czech fish that I now start with the assumption that all czech-bred fish are latent carriers of fish tuberculosis and/or have a compromized immuno system due to having been raised with prophylactic levels of antibiotics. When faced with the stress of shipping and the normal bacterial flora of a home aquarium most quickly get diseased and die.

[jar]

I am using the API test kit, not that old, so i assume it is fairly accurate.

It is an interesting point about where the source of the fish are. I had wondered if being wild caught would make them more susceptible to death... Not a single shop here in Melbourne is ever able to answer the question of the source of the fish, either they don't want to, or don't care enough. I have asked at many many shops this question!

[reneb]

sort of a late reply!

I only have 2 C. pygmaeus in my 29 gallon tank, so sample size is very small. Nonetheless, these 2 are thriving. They are actually in a slightly overstocked (but very well filtered) planted tank. I purchased these 2 C. pygmaeus at the same time about 6 months ago, and I've never had any suspicion that all is not well with them. They are active, and show every sign of being healthy.

I don't really have any clue as to why, but I can say I don't do anything 'special' (e.g. R.O. water, daily water changes, constant monitoring of water parameters). Thus, I am merely suggesting that, in my limited experience, this species is no more sensitive than my other cats in that tank: C. schwartzi, sterbai, metae, paleatus, robineae; Dianema urostriatum; Farowella; Otocinclus.

[apistomaster]

I agree with Mike Noren that Corydoras pygmeus are very sensitive and prone to high losses among newly imported fish.
All of those sold in the USA are wild caught and are as run down by the time they arrive as Otocinclus or Rummy Nose Tetras, Marble Hatchetfish;
all examples of fish which have uncommonly high mortality rates at the retail/home purchase level. Very similar to Aspidoras pauciradiatus in this same regard.
However, well acclimated specimens are not particularly delicate and will usually live long lives if kept in schools of six or more and receive regular feedings of live and frozen foods.
I have been breeding mostly dwarf Corys, hastatus and habrosus, these past 18 months and I have found that if they receive one daily feeding of live newly hatched brine shrimp nauplii or chilled down portions, in addition to other sinking prepared foods, they thrive and breed very abundantly in moderately soft water. I have provided my Aspidoras pauciradiatus with the same care and softer water but I haven't found any fry although I have spotted groups of eggs stuck on Anubias leaves. I rate Aspidoras pauciradiatus as a more difficult fish to keep and breed than C.pygmeus.

[Carp37]

I bought two batches of six at a Catfish Study Group auction last year (presumably home-bred but I can't confirm this)- I did lose two of them in the first week, but over a year later, the other 10 are still thriving, even though they've been bounced around my tanks to make way for fry of other species a few times. I wasn't surprised to lose a couple as you never know how long they've been bagged up prior to an auction (plus I had to drive >100 miles home), but I wouldn't say they've been especially sensitive once they acclimated. I do only get a headcount about once a month, as I can almost never see all 10 at once.

[apistomaster]

Their relatively extreme shyness is my one complaint about C. pygmeus. All the dwarf Corys are shy by C. pygmeus takes it to the extreme. Even keeping them in large groups(25 or more) doesn't help over come very much of their shyness as it does with C. hastastus.

[Marc van Arc]

Their relatively extreme shyness is my one complaint about C. pygmeus. All the dwarf Corys are shy by C. pygmeus takes it to the extreme. Even keeping them in large groups(25 or more) doesn't help over come very much of their shyness as it does with C. hastastus.

While at it (and slightly off topic): I find many Corys very shy. I recently sold my groups of sterbai, longipinnis, metae and melini/loxozonus due to the fact that they were simply invisible. Contrary to - for example - melanotaenia, which are always on the move.
With regard to the dwarf species: my pygmaeus are doing fine and the same goes for the habrosus. In my case hastatus has turned out to be very fragile, for they are going one by one....

[apistomaster]

Hi Marc,
I have found that feeding live chilled live brine shrimp nauplii to dwarf Corys an effective way to keep them in peak condition.
I raise both C. hastatus and C. habrosus in the hundreds and daily bbs is standard; they receive all they can eat once a day. C. habrosus are slightly more difficult species to keep well. The daily feeding of brine shrimp nauplii will also supply their newly hatched larvae with food and you should begin to see their numbers increase rather than slowly losing the adults.
I am familiar with their tendency to fade away over time but that will stop if they receive bbs regularly. They do not seem to thrive on only prepared and frozen food regardless of how high the water quality is kept. I still fed them these other foods in addition to bbs.
I sell a lot of C. hastatus but I would raise them for the fun of it even if I weren't selling them.
C. habrosus produce fewer but larger eggs and are not as productive as C. hastatus.
Just my 2 cents, as some one who breeds them commercially.

[mummymonkey]

Just to be contrary I've found pygmaeus to be more or less bullet proof. Probably the easiest cory to breed also. Just about their only negative attribute is that they can be shy but that applies to most corydoras spp.

[apistomaster]

Actually, I tend to agree, but like many fish, Otocinclus, for example, newly imported specimens tend to have high mortality rates. Once acclimated, they may thrive for years.

[Carp37]

Actually, I tend to agree, but like many fish, Otocinclus, for example, newly imported specimens tend to have high mortality rates. Once acclimated, they may thrive for years.

This might be the crux of it- wild-caught fish may suffer high mortality rates during and after shipping, but are OK once acclimated, whereas tank-bred specimens are relatively hardy anyway (assuming they're not going from one water extreme to another e.g. very soft to very hard water).

In terms of shyness, I have to agree they're pretty retiring- mine became less so with other small fish such as endlers, or other juvenile Corydoras, in their tank, but I keep trying to leave them on their own to see if they'll breed- no success yet on that score! Mine quite often rest in plain sight at the corner of the tank nearest the door when they think it's nearing feeding time (but promptly scarper when food is introduced!).

[Mike_Noren]

IMO there are two issues here, sensitivity and condition at purchase.

If you give a fish optimal surroundings there is no such thing as a sensitive fish. Even species renowned for keeling over at the slightest provocation will live normal lifespans and reproduce willingly if given optimal care. So, sensitivity, according to me, is instead how well a fish deals with suboptimal conditions. Some fish, like goldfish or guppy, will thrive almost anywhere, while others have strict requirements.

Then there is the issue of condition. Some wild caught fish, notably Otocinclus, have been starved and treated roughly for weeks when they reach the pet shop, and already have one fin in the grave. Others, like neon tetras, have been captive-raised with constant dosing of antibiotics to speed up growth, and effectively lack a functioning immuno system.
Both types are likely to suffer heavy losses after purchase, but the individuals which manage to acclimatise are also likely to live long and prosper.

I don't know where C. pygmaeus falls in this classification, but my impression was that the ones I bought were both in poor condition and sensitive to suboptimal environment.