River / blackwater fish and surface cover.

[seangee]

Some years ago when I had 50% of the surface of my tank heavily covered I noticed that my paracheirodon axelrodi (cardinal tetra) favoured the dark side. Recently I decided to re-create the look but this time only covering a third of the tank. Since those days I have added some trigonostigma espei (lambchop rasbora).
Their preference for cover is even more obvious as can be seen in the pic below. If I make a sudden movement or noise in the room both species immediately head for cover. The lambchops are pretty much always on that side except at feeding time. FWIW the nannostomus marginatus (dwarf pencilfish - now in a different tank) were also always in amongst the frogbit.

 

[seangee]

Just looked over from across the room and right now every single one is on that side. If I move they will so no pics now
The bottom feeders don't care and are doing their thing throughout the tank.

 

[Magnum Man]

my South American Tetra tank is highly shaded by pothos vines, between the light, and the tank, and most all the Tetras, 6-8 varieties all seem to like the darkest spots

 

[TwoTankAmin]

I wonder if in the wild they are preyed upon from above by birds? If so this might explain their liking to be under cover and out of sight from above. Or maybe, being colorful fish, in the dimmer lighting under cover they do not stand out as much? There is usually a practical reason for this sort of preference.

 

[anewbie]

Weird; my cardinals in a 100 blackwater aquarium seem to have no desire to hide; but the ones in the discus tank of course avoid the discus. My n. marilynae behave somewhat similar to your dwarfs forming a very tight group and retreating whenever i'm near the aquarium (but quickly come out when i put in food); while my n. epesi show no fear at all swarming everywhere.

 

[seangee]

I wonder if in the wild they are preyed upon from above by birds? If so this might explain their liking to be under cover and out of sight from above.

I suspect this is at least part of the reason. We know that SA tetras don't like bright light, but I see the same pattern when the tank lights are off. The room is fairly dark as I keep the blinds closed most of the time, and the lid is black, so there is no light or dark part of the tank. I also thought of birds and my assumption is that the behaviour is purely instinctive as most of our tank fish have no knowledge that birds even exist.
It does make me wonder if these fish are under constant stress if they don't have access to surface cover, even though they have no idea why they feel safer under cover.

 

[Essjay]

I had espei rasboras in the past and I before I had floating plants they were always together in a back corner. I bought some plants after reading a post by Byron. The fish stayed under the plant cover; as the plants grew and covered more of the surface the fish came further and further out of the corner, but never under the exposed surface.

 

[seangee]

I had a similar conversation with Byron a few years ago specific to cardinals. IIRC he said that in the wild they would venture a short distance out of cover as long as they knew it was accessible. Certainly in my tank they are much more visible when I do have an area of cover. When I removed the floating plants to eradicate duckweed you would never have guessed that there are over 30 in the tank as they used the substrate plants for cover.

 

[GaryE]

Birds are the main danger, as far as the fish are concerned. Open water at the surface is shunned by small fish. I've seen that in Mexico, Honduras and Gabon - and I've watched the fishing birds at work in the latter.

I think even for avoiding underwater predators, unless the fish is reflective silver, its camouflage doesn't work in open water. When you have the strongly marked fish we like, most of them seem to like shade.

If you ever go fishing in the jungle, drag a strong net up from under the shoreline vegetation. Along with the spiders and bugs, you'll find the smaller species of fish. It doesn't really work for cardinals, I guess, since they breed in the flooded forests where cover is everywhere. But in streams, you rarely saw the fish you were about to catch.

 

[seangee]

I had espei rasboras in the past and I before I had floating plants they were always together in a back corner. I bought some plants after reading a post by Byron. The fish stayed under the plant cover; as the plants grew and covered more of the surface the fish came further and further out of the corner, but never under the exposed surface.

That's really interesting and today they certainly have not come out from under cover. When I first put the two species together I concluded they interacted well because they were always in a single large group. But that was when I first started re-growing the canopy. Looking back through the photos as the cover has thickened they have progressively moved back into 2 distinct groups with the lambchops sticking closer together and more under cover. It seems that under pressure they opted for the additional security of being in a larger group, even if that meant mixing with foreigners.
The cardinals are much more spread out, but this may be because I have 30+ cardinals and only a dozen lambchops.

 

[seangee]

I could keep speculating ...
Or ...

It seems the rasboras prefer my dive torch to being out in the open
The tetras would rather avoid the bright light

 

[Innesfan]

My Brevibora dorsiocellata ("emerald eyes") clearly prefer no cover and are out in the open and avoid the shadows. Being so tiny and with those little beacons in their eyes I would have thought differently. The characins like the shade. The Pethia setnai and Hoplisoma metae don't give a darn though the latter when at rest prefer the shade.

 

[anewbie]

My Brevibora dorsiocellata ("emerald eyes") clearly prefer no cover and are out in the open and avoid the shadows. Being so tiny and with those little beacons in their eyes I would have thought differently. The characins like the shade. The Pethia setnai and Hoplisoma metae don't give a darn though the latter when at rest prefer the shade.

I have two groups one in a 29 which is a little more skittish - the aquarium water is lighter and plants on one side take up a lot of space; the other group is in a 100 (30x48 swimming area); that aquarium has much darker water and a lot more wood et all and they seem more comfortable.