Neale re: threadfins (Rainbows)    4/24/08
Hello again Neale,
<Hello Aileen,>
I have been fish keeping almost a year now and it amazes me how much I learn every time I look through pages of this site. Sometimes too much and the information gets all jumbled in my head (could be age too) and other times I learn enough to lead me to ask more questions.. it really is a wonder resource.
<Thank you!>
You mentioned some time ago that if I wanted threadfins I should consider another tank. I thought you were nuts at the time but...I am going to look at a used 40g tomorrow. Actually somebody had a 100g I can have but I think two monster tanks might be a bit much. My thinking is leading me to include in this tank: threadfin rainbows, wrestling halfbeaks, Corydoras and then I was wondering about bumblebee gobies or something with some colour. I was reading on WWM that most bumblebee gobies are considered brackish except one species, which may or may not, tolerate fresh water better?
<BBGs are complicated: you cannot possibly identify species; even scientists have trouble doing this under a microscope, let alone with live fish! Most BBG species seem to be found in a variety of habitats, from blackwater streams to brackish water. But in aquaria they are temperamental, and slightly brackish water does seem optimal. This is a lot like Mollies for example, which may be freshwater fish in the wild, but unquestionably are easier to keep in brackish. Because BBGs are very difficult to keep well fed, I'd not keep them in a community tank.>
My water is liquid rock. What are your thoughts on this community and any numbers you may think appropriate? Are there any other species you might include instead?
<Almost anything that doesn't explicitly need soft water should thrive. pH stability is more important than pH value in most cases, and people routinely keep all sorts of things in hard water conditions. With Threadfin Rainbows, I'd be looking at Corydoras (and their relatives, like Aspidoras and Dianema) in terms of bottom dwellers. Kuhli loaches and small Loricariidae such as Whiptail Catfish would also be appropriate. You might also opt for some surface fish like Halfbeaks. Tetras and Barbs are best avoided because of potential problems with fin nipping, but Rasboras and other small Rainbowfish are certainly an option. Livebearers are certainly a possibility, though some Goodeidae are fin nippers so choose with care.>
And since I have your attention, I was reading on here some time ago about separating swordfish fry before the appearance of the sword to prevent inbreeding. So I immediately set up another 10 gal to do so. But I realized when I was trying to sex them that they appear to be all female! Is this a probability?
<No. While the idea that Swordtails change sex is widely held, there are actually no scientific studies that backs it up. It is much more probable that aquarists mistake undeveloped males for females. Male livebearers don't develop their sexual characteristics until a certain age (usually around 2-3 months depending on the species). Obviously until the gonopodium is formed they cannot fertilise the females, so you don't need to separate them until that time.>
Or am I missing something like the triangular fin I am supposed to be seeing on only the females? Is the differentiation not as great in fry as adults? I ended up separating by size as it seemed the best alternative at the time. Since I was having so much trouble purchasing healthy vibrant red swords I decided to keep the try of a lone surviving, vibrant female. The batch was small but healthy, I have not lost any and they are about 5 months old. But still, not a sword in the bunch...I was hoping for some nice deep red males for another long term plan.
<If you have just 5 fry, it is statistically possible, though unlikely, they are all one sex. But if the fry are less than a couple months old, you can't sex them anyway.>
Thanks in advance for your help
Aileen
<Good luck, Neale.>