Raisin' Fish: Early Maintenance

Last Wednesday, Francis and I spent a good portion of the day in McAleer Creek. We were doing early system maintenance on the piping going from the inlet to the clarifier/incubator setup.

The most important factor in raising healthy fish is to assure a steady supply of clean, cold water to the incubator, preferably at a flow in the range of 10 gallons per minute. As long as the water is flowing, the eggs and fish are going to get all the oxygen and nutrients they need directly from the water. Before the eggs hatch, all they need is the water flow and oxygen. After hatch, they don't need any food until late in the process when their digestive systems have started to develop. So, mostly they just need the oxygen in the clean, cold water.

I've probably explained before that we have about 500' of 2" plastic pipe running upstream of the incubator. At the head end we have a 6" pipe with lots of 1/4" holes drilled in it sunk in a large pool of water. Because that pipe is at a level higher than the outlet pipe of the incubator, gravity drives water through the system pretty efficiently as long as there are no blockages or major air bubbles in the system.

We've got the inlet pretty well sheltered to keep debris from entering the pipe, so blockages are not much of a problem (haven't been during the previous 10 years anyway), but air bubbles are another matter. Cold water carries a lot of oxygen in solution (the colder it is, the more it carries - think of a glass of water you let warm up - bubbles develop on the sides of the glass as the oxygen comes out of solution when the water warms up). Turbulent creek water also carries air bubbles. As the water flows through the pipe, those bubbles collect in high spots in the piping. If the bubbles get too big, they restrict water flow.

We do two things to combat this. First, we try to keep the piping at as even a slope as possible, so that there aren't as many places for the bubbles to collect and they eventually find their way all the way up to the inlet end. Second, we bleed air out of the pipes at the junction where two pipes come together. We use standard plumbing piping that we get from Home Depot (2" black ABS plastic) that comes in 10' lengths. We join lengths together using white 2" heavy duty collars (they're much deeper than the black ones with more surface area to hold both pipes) and stainless steel sheet metal screws. Those screws double as our bleed mechanism. We make sure that when we screw the pipes and collars together, the screw heads are pointing straight up at the top of the pipe. Bleeding the system then involves nothing more complex than backing one screw out of the hole and letting the air escape.

Bleeding the system is kinda contemplative; I just put on my waders, grab a portable drill with a Phillips head driver and start walking upcreek from the incubator. At a junction of two pipes, I back out one screw. If water comes out, then there's no air to bleed so I put the screw back in and continue upstream. If I hear the hissing of air, then I wait until water does come out, then put the screw back in. It's a nice quiet walk up the creek and I get to check out what's going on in the creek at a fairly close and slow rate.

When we first put all that piping in, it was all in the creek and just followed the curves of the creek downstream. This led to lower reliability for a couple of reasons. When the water gets high after a rain, the creek flushes alot of branches, rocks, sticks, leaves etc down the creek. Some of that stuff can lodge under the piping, lifting it out of the water and destroying its ability to flow water. Very bad for the fish. The other problem is more insidious. The constant motion of the creek pushes the pipe against the stones over and over. Eventually, this wears a hole in the pipe and you lose water pressure to the system right there. If the pipe is in the creek, you don't see the leak. You have to run your hands over the entire 500' of pipe, checking for leaks with your hands.

A couple of years ago, Francis and Joel (a family friend who works around our place occasionally) took all of the piping out of the creek and put it up on the bank. This makes it easier to bleed and much less likely to spring a leak. We did have one problem area that had been nagging at us for the last couple of years and it wasn't until last week that we fixed it.

At one point in its downstream travels McAleer Creek makes a big curve around a small hill. We took the pipe right over the hill, digging a trench for the pipe so it stayed more or less level. Over the years, the trench filled in with dirt, leaves etc and became somewhat hard to find, and, even harder, to bleed. We spent part of Wednesday digging the pipe out of the dirt and repositioning a bunch of it to make it easier to bleed and maintain.

The incubator is now flowing clean, cold water at a rate of 10+ gallons per minute. We won't need it for a couple of months (the eggs need 750 thermal units from fertilization to hatch, so I'll probably get them in about 60-65 days or so - late December/early January), but we are ready. It feels good to be prepared.