The darkness and the light

[GaryE]

I got two new to me tetras this week, Hyphessobrycon rubrostriatus, a silvery one with strong red markings, and Hyphessobrycon melanostichos, a stunning reflective blue-green metallic fish with a black line. I put them in a 36 inch, one metre tank, well planted and filtered. They're in QT for 6 weeks, til I decide which SA tank they go into.

Both these fish have darker body markings, although there is a lot of red in the rubros. In the afternoon, sunlight angles into their tank from a window, but it only reaches about 1/3 of the aquarium. I wanted to see their colours in natural light, and I discovered something unoriginal but interesting. Both groups of 10 fish had formed a large shoal, and were avoiding the bright water. There was a sharp shadow line between sun and LED lighting, and they would swim right to the edge of it and then wheel around back into the relatively dimmer part of the tank. Until the sun moved away, not one of either species went near the intensely sunlit regions.
These guys have seen sun before. Last week, the rubros were in Colombia.

I think it says something for all the aquascapers out there. Bright blazing light and no cover is not good for darker bodied tetras. The completely silvery ones often use it for camouflage, but even these rubrostriatus, silvery to a point, avoid the light. It makes sense. Predators, be they birds of fish, can see them better.

I'd suggest we should all make sure our tanks have shaded areas, and we should watch how the fish use them. There is a balance to be struck between plant growth and fish comfort.

 

[Essjay]

I thinned out my red root floater as usual last week but on this occasion I over did it. For the last week, only the third of the surface at the opposite end of the tank from the filter has been covered. When the tank lights are on, both cherry barbs and harlequin rasboras are spending almost all their time under that small patch of floating plants, apart from when one or more of the male cherry barbs decide to chase a female into the non-covered bolbitis. Needless to say, I did not remove any floaters this week, and I'll wait until the surface is completely covered before thinning it again. Lesson learned, don't get carried away when thinning out floating plants.

 

[gwand]

I instinctively focused my light source on 1/4 of the tank. I’m glad to know that for once my instinct was correct. Ha ha.

 

[Magnum Man]

I try to maintain about half of my tank open, and half covered densely in water lettuce… most of the African tetras don’t seem to mind one side or the other, and I have 2 Nicrew LED lights full length over the tank, as it’s so deep, they cross the shadow line without hesitation… the 3 line glass cats, however, are center of tank swimmers, but they are almost always under the water lettuce, except at feeding times, and now that I’m watching, the Brichardi seem to prefer the shade

 

[GaryE]

The brichardi are said to be creek fish, so they would like shade.

Most of the usual mid-sized Congo River tetras are out in the flow, and the standard Congo tetra is a sun worshipper.

I've never dug into the how the cats live.