A balance of darkness and light

[graye]

I've recently added two new tetra species to my collection: Hyphessobrycon rubrostriatus and Hyphessobrycon melanostichos. The rubrostriatus boasts striking red markings on its silvery body, while the melanostichos has an eye-catching blue-green metallic sheen with a black line running along its body. I've temporarily housed them in a well-planted 36-inch tank with ample filtration.

Both species have darker body markings, with the rubrostriatus having a notable amount of red. When sunlight enters their tank from a nearby window, it only reaches about a third of the aquarium. I was curious to see how they'd react to natural light, so I observed their behavior. Interestingly, both groups of 10 fish formed a large shoal and avoided the brightly lit area. They'd swim right up to the edge of the sunlit region, then quickly turn back into the dimmer part of the tank.

This behavior continued until the sun moved away. It's worth noting that these fish have likely encountered sunlight before – the rubrostriatus were in Colombia just last week.

This observation has implications for aquascapers. Bright, unobstructed light can be detrimental to darker-bodied tetras. Even the silvery-bodied rubrostriatus, which might seem well-suited to bright light, avoided it. This makes sense, as predators – whether birds or other fish – can spot them more easily in well-lit areas.

I recommend that we all ensure our tanks have shaded areas and observe how our fish use them. There's a balance to be struck between promoting plant growth and maintaining fish comfort.

[sSjey]

I recently pruned my red root floater, but this time I overdid it. The result was that only a small section at the far end of the tank, opposite the filter, was left covered. Now, when the tank lights are on, my cherry barbs and harlequin rasboras are practically living under this patch of floating plants, except when the males get a bit too enthusiastic and chase the females into the open bolbitis. I've learned my lesson - I'll be more careful with the pruning shears from now on. No floaters were removed this week, and I'll wait until the surface is fully covered again before thinning them out. It just goes to show how important it is to strike a balance between plant growth and providing our fish with the cover they need.

[wandg]

My gut told me to limit the light to a quarter of the tank, and it seems that was a good call for once.

[bettaMagenta]

I've found that my African tetras are pretty adaptable, they don't seem to have a strong preference for either the open or densely covered areas of the tank. I've got two Nicrew LED lights running the full length of the tank, which helps to create a nice shadow line, and they're happy to cross it without hesitation. However, my three line glass cats are a different story - they're generally found swimming in the center of the tank, but they almost always seek out the shade of the water lettuce, except when it's feeding time. Now that I'm paying closer attention, I've also noticed that my Brichardi seem to prefer the shaded areas, they tend to congregate under the water lettuce.

[graye]

I've always thought the Brichardi's creek origins would make them shade lovers, and it seems that's the case. The Congo River tetras, on the other hand, tend to thrive in the flow. The standard Congo tetras, in particular, seem to have a thing for sunlight. As for the glass cats, I've never really looked into their natural habits, but it's interesting to see them gravitating towards the shade in my tank.