Catch & Release
We STRONGLY recommend catch and release fishing only. If you like to eat fish, consider stopping by your local supermarket on the way home. Leave the fish in the water for others to enjoy for years to come. By the way, it is a myth that the trout don't survive the summer. I have caught them in late August after several months of 90+ degree weather.
How to Safely Release a Fish
When you catch a fish, try to minimize the amount of time it spends out of the water especially during the hot summer months when the water is warmer. After removing the hook, hold the fish under the water facing upstream to give it time to catch its "breath", gently cradling it under its belly while holding its tail. Continue to hold the fish under the water until it swims out of your hand.
When possible, use a knotless net, barbless hooks and don't fight a fish too long. Long fights increase lactic acid buildup in the fish lessening its chances of survival.
Another tip: Don't try to remove deeply embeded hooks. Simply cut your line. The hook will rust out with time preserving the fish's life.
TPWD Fishing Regulations
If you feel you must take fish, here are Texas Parks & Wildlife's regulations:
"In the Guadalupe River in Comal County from the second bridge crossing on River Road upstream to the easternmost bridge crossing on FM Road 306, rainbow and brown trout may not be retained when taken by any method except artificial lures. Artificial lures cannot contain or have attached either whole or portions, living or dead, of organisms such as fish, crayfish, insects (grubs, larvae or adults) or worms, any other animal or vegetable material, or synthetic scented materials. This does not prohibit the use of artificial lures that contain components of hair or feathers. It is an offense to possess rainbow or brown trout while fishing with any other device in that part of the Guadalupe River defined in this paragraph. For rainbow and brown trout, Minimum Length Limit= 18 inches and daily bag=1 fish."
Parks & Wildlife Department