Moments of Clarity, Part II — Rainbow Trout

If successful, I will have the first rainbow trout farm in Laos. If.

One of the main reasons I ventured up onto the Bolaven Plateau was to check if the water temperature and volume were sufficient to farm rainbow trout. The King of Thailand has a Royal Project at Doi Inthanon in Chiang Mai. According to my sources, they can’t produce enough to meet domestic demand. It’s at a similar elevation of over 1,000 meters. If successful, I will have the first rainbow trout farm in Laos. Big “if,” though.

The weir on the middle tier.

The biggest issue is water temperature. It has to be cold enough. I’ve been monitoring it for a number of months now, and it has only once reached a borderline high of 22 degrees C. Mostly, it’s been between 17 and 19 degrees. The optimum temperature is 16 degrees. That’s the environment in which they eat the most and grow the quickest. Another issue is flow. Rainbow trout need a lot of well-oxygenated water. The photo here was taken in early September. I’d say it’s got about a third of the flow now that the dry season has set in, but still a cubic meter or more per second.

Farm-raised rainbow trout are usually raised in raceways, which are basically artificial streams, often made out of concrete. In the flow-through method, water is channeled from up stream through these raceways and returned to the source further down stream, relying on gravity to do the work. I’d been struggling with how I would work this out. Raising the water level up stream helps, but it’s a lot of work to channel it, not to mention having to construct the raceways, which I was going to do using pond liners instead of concrete.

15 or so meters up stream of the weir, this is where I'll raise the water level by 40cm and contain my rainbow trout.

But then came my moment of clarity. Why create an artificial stream when I’ve got a real one going straight through my land? Why use a fraction of the flow when I can use all of it? Duh. If the stream formed the border between my parcel of land and the next, I can imagine the problems, but from one point on the middle tier to one point at the far end of the bottommost tier, the stream is entirely on my property. Shortly after it exits my property, it joins a much bigger stream, a river, actually, so the environmental impact of, say, 10,000 rainbow trout peeing and pooing in the stream is worth noting, but not worrying. I’ve seen nothing larger than a minnow so far so I doubt any barricades that I put up to contain the trout will match the 14-meter waterfall just down stream, in terms of preventing the migration of any natural critters. I have to fly in what are known as eyed eggs from the United States and hatch them myself. They will all be certified females, so their accidental escape does not pose a long-term threat to existing critters, either. By constructing the Irish Bridge I’ll be able to increase the water volume behind it by 50 to 100 cubic meters from its existing 50 to 100 cubic meters (I’ve got some measuring to do when I’m there next).

And what does one do with 10,000 rainbow trout, you may ask? Well, besides sell them, I’ll charge people to come and catch them.



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