After three years of meticulous research, Brenda and J.C. Lyons took their savings and built a prawn and fish farm. They bought a house and barn in Sandoval, Ill., 60 miles east of St. Louis, and went to work. Two years later, with $180,000 invested, the Lyonses run a prawn hatchery, a nursery and raising ponds. They have buyers both for juvenile and full-grown prawns - large or fresh-water shrimp. They also market and sell fish from other Illinois farmers. They've applied for a federal Department of Agriculture grant to begin raising three types of fish - hybrid striped bass,...