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Since you mentioned fish and farming, I'll make an off the wall suggestion. Have you ever heard of Aquaponics? It is a hybrid of fish farming and hydroponics. In Hydroponics you use chemicals to control water purity and fertilize. Aquaponics eliminates that by using a stock tank of fish as the fertilizer source, and a grow medium (gravel, expanded clay, etc) as the filter. If you are interested check out backyard aquaponics forum. There are several people in Texas doing it and a lot more throughout the world (heaviest concentration seems to be in Australia). It is more conservative with water since it is a closed system. The water cycles from the fish tank to the grow media, and then back again.

My dad successfully gardens in the hill country (Boerne) the normal way. A lot of parts of Texas can be used for gardening if you are willing to put in raised beds if the soil is poor. This is fine on a small scale, but expensive if you wanted more than a "backyard" garden. My father in law successfully gardens in Houston the normal way.

I have done Aquaponics for a couple of years and then gave it up (I am a lazy gardener unfortunately).