Effect of surface plants on forest fish

[seangee]

Some of you may remember that some time ago I cleared the frogbit from the SA tank to allow me to tackle the duckweed. Well one thing led to another and along the way I forgot why I had them in the first place. Earlier this year I made a concerted effort to clear the duckweed and re-introduced some frogbit which now covers more than 50% of the surface. Most significant observations:

1. I can pretty much see all of my cardinals all the time. I have enough that you can't miss them, but many would often be down in the plants. Now they are happy to stay out in the open (from the perspective of my chair ) because they are secure in the fact that nothing is going to swoop from the sky to catch them. I don't actually have birds in my living room but you don't just suppress thousands of years of instinct. I may even add a few, although according to sites like aqadvisor this tank is already well overstocked and under filtered
   
2. I have 2 pencilfish (nannostomus marginatus). The group was decimated in late 2019 when my sids became sexually mature and went on the rampage leaving only two alive. After I got a new tank for the sids I did occasionally think about replacing them but had more or less made up my mind just to let them live out their lives as their behaviour was so similar to the cardinals. They lived in the lower half of the tank, often concealed by plants and only came to the surface to sleep once the lights went out. I assumed that this was for security because the group was so small that they adopted the cardinals as their own. Well I was only half right (it was for security), now they are back to spending almost all of their time at the surface and I am definitely going to order a few friends for them - say 15-20 so I will have fish at all levels of the tank.
3. Watching the corys (c.paleatus) swimming upside down foraging amongst the roots is really cool ...

 

[Byron]

This is very informative. Thanks for posting.

During an investigation reported in TFH by Geisler & Annibal (1987), repeated observations in the biotopes of Paracheirodon axelrodi (cardinal tetra) indicated that the fish avoided the more strongly lit parts of their favourite waters and that their habitat ends almost to the centimeter on the border between shade and sunshine.

Another interesting observation made by someone whose name escapes me at the moment noted that in habitat waters full of branches the cardinal tetras were in smaller groups of six and seven, and there were many of these smaller groups within a larger area all within easy sight of one another. But in more open waters, they were in the hundreds in one shoal.

 

[WhistlingBadger]

Very interesting, Seangee. It makes a lot of sense. Thanks for sharing.

 

[seangee]

During an investigation reported in TFH by Geisler & Annibal (1987), repeated observations in the biotopes of Paracheirodon axelrodi (cardinal tetra) indicated that the fish avoided the more strongly lit parts of their favourite waters and that their habitat ends almost to the centimeter on the border between shade and sunshine.

That corresponds with my own observations. Previously I had the right hand side of the tank covered, as in my signature pic. The cardinals habitually stayed in the shaded half, its even apparent in the picture.

 

[GaryE]

I'll offer a step further. I keep West African killifish of the Genus Aphyosemion. They are notorious for jumping out of tanks when startled. So, tight lids all around.

However, I like house plants. If I grow terrestrial Monstera right beside tanks, with their big leaves overhanging, I get no jumping. My paludarium is a low 40 with plants hanging over it, and has to be open topped. I have never found a 'fish chip' on the floor, and the previously skittish fish in there display constantly.

In tanks with water tolerant terrestrial plants rooted in the water, with leaves spreading along the top glass (Pothos, a variety of vines, peace lilies....) the fish are many times more visible. I'm thinking our tanks should not be separate units in rooms, but part of a room along with growing plants.

Why?

The big predators for small fish aren't usually fish. Tiny species tend to move through shallow water to avoid predators. But that exposes them to birds, and small fish are hardwired to react to shadows. The average tank stand is 30 inches/76cm in height. Add the tank. How tall are you? Do you cast passing shadows? Ever wonder why commercial tank lids only have a small area that lets light in?

The famous forest canopies do a lot. Very little light hits the forest floor. In regions of small rivers that run down mountains or from higher ground, the water can be several degrees cooler than we keep our tanks because of this. No sun, no heating up. In Amazonia, during rainy season, cardinals move into the trees and colonize the forest floor. There is a lot of food, but it is very dark. When dry season clears the forest floor of water, they move into the streams again.

I have not been to South America. I wish I had, and I hope to go to Colombia before I get too old. But fish-exploring friends go regularly, and I have watched a ton of go pro video - days of it over the years. Cardinals form enormous shoals in dry season. Rummy noses are fun to watch in the wild. Discus and angels seem to like water lily pads above them.

The more touristy video, above water, shows a lot of birds.

 

[WhistlingBadger]

I have had marble hatchets for several years. They are notorious jumpers, but I still have at least seven of the original ten, despite their tank being in a public space with several openings in the lid. My tank usually has a thick covering of java fern and frogbit which covers over 50% of the surface. More like 75% most of the time. I suspect that is why they have stayed put.