So we've kept a 20g tank full of guppies for about 4 years now. It has 7 types of plants, all doing well. As well as a population of guppies that we've been manipulating for about 3 years. We began this project with a handful of guppies and a few other fish, the idea that the other fish would enjoy the fry. Oh yes they did. Right up until they grew too big and got sick and had to be destroyed. But the guppies soldiered on, bolstered during the first couple of years by irregular introductions of especially pretty males from the same store that we bought the original stock from. Generally speaking, we chose to add yellow/red. Tails were average MFS [megafishstore] size, though generally very well saturated.
The first year there were quite a number of deformities. We did not cull any fish during this phase. I was also experimenting with live plants, and found that the same goodness that's been keeping my houseplants lush is great for plants you stick right into the water. The population quickly topped out near it's current max of about 3 dozen adults and at least twice that in fry and juveniles. I didn't cull any because I figured any lethal combinations would sort themselves out eventually. Once the anomolies bred themselves into extinction, there was a preponderance for blue bodies, light blue dorsals and red tails. In between these, were occaisonal "rainbows" and even rarer were yellow with red spots, we call "clowns". I began a pogrom against the blue body/orange tails. Clearly orange tails are either dominant or attached to some combination of morphology/behavior that makes a very successful male. I'm still seeing lots of orange streaks on the tails of the current population. For most of the fal and through the winter, there really weren't a lot of fry surviving. The population was very slowly dwindling. The water wasn't a problem, it was the tank setup. There weren't any places for them to hide, and they were getting eaten. The few that made it past mealsize did really well. So I invested in better plants and the population is back to where it was a year ago.
For the last couple of months, I've been examining the population without culling at all. The problem was that I liked all the little fellas. We had lots of rainbows and not a few clows, and no explicitly blue bodied/orange tailed males at all. At the same time, I lazily let an algal infestation get a little out of control. But in my quest to reduce nitrates and phosphates, I've decided to change my culling criteria. For nearly three years, I've been selecting against certain traits. I had to find a way to favor specific traits.
The first problem was deciding what traits to work on. I thought about body color or shapes of spots. But thats anathema to my chaotic sensibilities; the whole reason for this project is to watch the slow kaleidoscope of nature in all it's varied and random and unpredictable glory. I had to choose a specific trait that I could quickly and easily make a go/nogo decision. I eventually decided to work out the tails. I like all the bodies, and that was the most important trait. Now I'm going to get rid of translucent and or orange or striped black tails. I've got some guys with just gorgeous metallic blues and greens with traces of red and yellow. And the clowns tails are yellow and red streaked, but they are also translucent.
Once I established my new criteria, I also changed my culling method. I have a lot more plants than I did the last time I was trying to chase down fish. And the plants were smaller. My new method is to use the smallest net I can find and just hold it about 2 inches under the water at a shallow angle. The fish crowd around for a meal and often swim into my net of their own accord. If a male that meets my culling criteria swims where I can scoop him up, he's out of the gene pool. So I've removed 12 males and 2 sick females in the last month. It'll be interesting to see what they look like after a couple of generations of this.
I use a Penguin 200 which is theoretically able to filter 100% of the volume every six minutes. I don't think mine is that efficient, but it does keep the water clean. My substrate is just 1cm gravel, about 3-4cm deep. It's tragically underlit by one 18w 24" "plant spectrum" light, which the plants definitely like to grow towards.
Also filed under pacific nw life ♠ 
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