Fish Farm with Cages!

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SITING CAGES

The ideal site for a cage will be a spot where the water is about six feet deep. Shallower locations will normally have reduced water circulation, while some deeper spots are subject to "turnover" . . . a sudden reversal of water layers that brings deoxygenated bottom water to the surface. Caged fish that are caught in a turnover may be killed.

Try to choose a site that's exposed to breezes but protected from high waves and motorboat traffic. Consider, too, that if you can set your cage off the end of a dock, you won't have to boat out to feed the fish. Should you need to site the enclosures in open water, do secure them with at least two anchors—one at each end of the cage—fastened with nylon lines. And always put your cages out before you're ready to stock them ... so you can make sure they float properly.

STOCKING

A delicate, indeed critical, moment in any aquaculture operation is stocking ... the transferring of the captured or purchased fish to their permanent home. You should always transport your stock in large, double plastic bags that are filled halfway with water and have plenty of air inside. (Commercial suppliers often pack their shipping sacks with pure oxygen instead of with ordinary air. Don't waste that valuable element by opening such bags prematurely.)

Begin by floating the fish-filled sack in your cage, and checking the water temperatures of the enclosure and of your container. Unless the two temperatures are nearly identical, you'll have to wait for them to equalize. The process (which usually takes from 15 to 45 minutes) can be speeded up by carefully exchanging small amounts of water between the sack and cage ... but if you try this, be sure you change the water temperature gradually. Too drastic a jump can either kill the fish outright or lower their resistance so much that many will likely die later on.

When the two temperatures have equalized, submerge the bag, tilt it sideways, and allow a few minutes for the two fluids to mix. Only then should you move the bag to encourage the fish to exit.

In general, stock your cages when the ambient water temperature is slightly below the range of desirable growth temperatures. That would mean introducing trout into 50-55°F water, tilapia in 70-75° ponds, and the other species discussed here in 60-70° water. Consequently, in most cases you'd probably want to stock your cages in the spring.

However, in many areas, larger, more vigorous stock is often available in the fall. If stocked then, these fish can be overwintered and "finished out" during the following spring and summer. Or if you live where hard freezes are not a problem, you can even stock young fish in the fall for overwintering. Remember, though, that fish set out in autumn won't grow appreciably during the cold months. (In warm southern climates, trout can be successfully reared in the winter.)

The size of your purchased fish (if you do buy any) will depend on your budget. Smaller ones are naturally less expensive. However, if you can afford it, stock the largest young fish you can obtain ... because they'll outgrow their little kinfolk and will have a higher survival rate.

And just how many fish should you stock? Well, to figure that out, you have to calculate backwards from your anticipated harvest, keeping in mind that the carrying capacity of a cage is the weight, not the number, of fish it will support. I've already indicated that you might expect to raise about 200 pounds of fish in a 50-cubic-foot basket. However, since most cage culture depends upon a growing season of six months or less, you probably won't be able to produce fish that average more than 3/4 pound each. Actually, I think 1/2 pound is an excellent pan size for the majority of species. (It's also an efficient size, since fish grow fastest when they're small.) Therefore, if you intend to produce 200 pounds of 1/2-pound fish, you'll want to rear 400 individuals. So, allowing for some mortality, you could stock a 50-cubic-foot cage with 440 bullheads, trout, or whatever.

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