The United States Fish and Wildlife Service has developed another plan to designate critical habitat for a pinky-size threatened fish. The agency proposes 1,244 miles of rivers in Arkansas, Texas, New Mexico and Oklahoma as critical habitat for the Arkansas River shiner. But the agency also proposes to establish a nonessential experimental population of the fish. That would reduce the size of the critical habitat to 826 miles by removing the range for the experimental population from the designation. In Texas, the Canadian River in the Panhandle would be part of that habitat. A year ago, a federal judge in New Mexico dismissed a 2002 lawsuit by a coalition of agricultural and ranching groups. The dismissal came after the Fish and Wildlife Service agreed to scrap its critical habitat proposal and come up with a better plan.