Generally, you would have large amounts of fish at the surface gulping for air if it were an oxygen depletion, not just one or two at a time. largemouth Bass would probably die before Bluegill. It would be good to test the water for oxygen...this is usually best performed and interpreted by an aquatic biologist, but you can get a cheap kit if you want to check it out yourself. The Koi Analyset on our web site has an oxygen test that is not highly accurate, but it will tell you if you have a severe depletion. Other aquatic companies offer better kits, and more expensive ones. Oxygen levels that are lethal to fish vary with species, temperature, duration and a few other factors, but usually Largemouth Bass will begin to die off around 2 or 3 ppm and Bluegill will begin to die off around 1 ppm.
Fish coming out of winter are often in compromised health due to being dormant all winter, and fungus on a few of them is not uncommon, especially in northern states...I don't know about Texas. If it is just a few fish I would not worry about it. If it were a few dozen, then I'd get an aquatic biologist in right away.
Clear water doesn't directly have anything to do with oxygen levels. The water coming out of our well is clear as can be, but it is void of oxygen. However, oxygen depletions in lakes generally are associated with decomposing vegetation, which can cloud the water.
