Jenynsia Onca Biotope tank build

[junebug]

Hiya Bill! :P Nice to see you in the fish area lol.

The fish have totally clear fins, so it's hard to determine gender in pictures. I have one clear shot of the largest male, but you can't see his gonopodium in it because of the angle. Let's just get some cool fish pics on this thread to oggle anyway, though

I haven't added the leaf litter yet. I put in the rest of the plants today, or at least most of them (I owe this tank two more Uruguay swords but it seems silly to order just two plants from my supplier, so it'll have to wait until I need more lol.) I wanted to see what kind of room I had left. I'm also looking for a moss to coat pieces of the driftwood, but I was impatient obviously, and put the wood in the tank already, so that may not actually happen.

Diatoms won't be an issue, though. This tank is what I like to call a natural light tank, in that I don't have any daylight spectrum bulbs on it, so it lives off sunlight. IMO with other tanks in this exact position, I'm going to see only green algae, given the amount of sunlight it gets. And then, I'll be getting algae eating catfish (you know, ones that actually eat algae... not cories or plecos lol) and a mystery snail for cleanup. Quick google searches of apple snail sites say the true mystery species is extremely common all over Uruguay and Brazil where these fish are found, so it seems a perfect match. Plus mystery snails are really easy to source lol.

Great news! While typing out that novel above, I scrounged through my photos and found some somewhat clear pics of each gender.


This is the only female of the 5 I got. She's a great big sweetie lol. As you can see, she has no gravid spot. With her coloration, I don't expect to ever see one. Often white fish, or fish with white bellies, don't get a visible gravid spot. There's just enough opacity that it covers up the dark coloration. Anyway, she's the big one in the middle, the others are all boys. Please excuse their clamped fins - I'd just added them to the tank, so they weren't really settled in yet.


This is the largest male. He's only a tiny bit smaller than the female, but has a clearly developed gonopodium so he's definitely a he. I can only assume that with decent feeding and growing room, the males of this species aren't tiny, like you'd expect to see with guppies. They are incredibly non sexually dimporphic. It took a long time for me to determine that I had only one female, and I've been sexing livebearing fish for quite a while now.

The fish are more active every day, and beg for food whenever they see me in the kitchen. If I walk up to the tank, though, they all still swim to the back. I think it may take a few generations raised in captivity before they get totally domesticated.

Edit: I just realized I never updated. I was researching the catfish found in the area, as they are much easier to find information on, especially the cory species and oto flexilis, and as it turns out, Jenynsia Onca are most likely to be found in clear water that happens to have a low pH. So I'm building a blackwater tank without blackwater LOL.