Use the lower rates on freshwater fish. Some species are very excitable and sensitive to handling and hauling stress. Anesthetics are useful for sedating such fish, and to reduce the metabolic activity. This means less oxygen consumption and less carbon dioxide and ammonia buildup. Also, energy is conserved which is available for maintaining ion balance.
Fish can be over-anesthetized and die.
Broodfish and species like redfish, largemouth bass, and hybrid striped bass respond well to anesthetics. A popular anesthetic is MS-222. It is approved for use on food fish, and a 21-day withdrawal period is required before fish are consumed. The recommended level of anesthesia during transport should permit fish to be caught easily by hand but not cause total loss of activity or equilibrium. MS-222 is used at 15 to 66 ppm for 6 to 48 hours to sedate fish during transport.