Many people who care about the health of salmon populations do not understand how society can expect loggers, farmers, miners, industrialists, and others to avoid harming wild salmon populations while hatchery programs are allowed to harm wild salmon. Safeguards, such as killing surplus hatchery salmon rather than allowing them to swamp an already depressed wild population, are being implemented to avoid or reduce inadvertent harm to wild populations from hatchery programs. The other is the hagfish. They are both jawless fishes belonging to the taxinomical class Agnatha. Although sturgeon and catfish can found in the same habitats and they both have barbels, they are not closely related.
Sturgeon are much more primative than catfish.
In North America, the white sturgeon is the largest freshwater fish. They have been reported to reach lengths of 15 feet or more. The second largest freshwater fish in North America is the alligator gar. The beluga sturgeon in Russia is the largest fish in the world that can be found in freshwater. This is a very broad question, and difficult to answer without a bit more context.