As Webster 1913
states so well, any slender marine fish
of the genera Belone and Tylosurus. The QPB
Science Encyclopedia adds that these include several different types of fish, but all within the Order Semionotiformes and Beloniformes, and are "primitive bony fishes".
What I'll add is that they have a nasty set of teeth, at least nasty compared to fish one would usually find in a Texas freshwater creek.
In addition to whatever hidden actions these fish take place in underwater, they spend a lot of time floating on the surface, eating. I observed them a lot while fishing at my Grandmother's creek. Anywhere from one to three of them would appear at one time.
One night, I was bringing in my line. All of the sudden, my line went under, and I had quite a fight on my hand. As I finally reeled in the fish, I noticed that it was long and looked strange. I got it onto the bank and noticed it was a gar. What an ugly fish, it had a snout that was about 3 1/2 inches, full of long teeth. Yikes! Needless to say, I didn't bother trying to retrieve my hook.