Fish General

Yes. Lamprey and hagfish are both jawless fishes. They are the only living members of the taxonomical class Agnatha (Greek for “no jaws”). 
No. Although sturgeon and catfish can be found in the same habitats and they both have barbels (whiskerlike growths extending from the jaw), they are not closely related.
Yes, sturgeon really are the largest of the freshwater fish. The beluga sturgeon in Russia is the largest freshwater fish in the world.
The USGS Grand Canyon Monitoring and Research Center in Flagstaff, Arizona, conducts at least eight trips each year to study endangered fish populations.
Coastal marshes provide essential habitat and nurseries for fish and habitat for migratory and non-migratory birds, mammals, reptiles, and amphibians.
Yes. Gas bladders, more commonly referred to as swim bladders, allow precise control of buoyancy because the volume of gas they contain can be regulated with ease. Two types of swim bladders exist.
This is a very broad question, and difficult to answer without a bit more context. Pollution comes in many forms; chemical, thermal, acoustic, and physical for example.