Below is TPWD's reply copied directly:
When we examine the law,
Texas Parks & Wildlife Code, Sec. 66.011. LEAVING FISH TO DIE. A person commits an offense if the person leaves edible fish or bait fish taken from the public waters of this state to die without the intent to retain the fish for consumption or bait.
As there is a segment of the public that enjoys angling for rough fish, I would suggest they have a value beyond fertilizer. Some of the public actually enjoys consuming what others say are rough fish.
In light of this, I would say your described practice is a violation of 66.011.
Assistant Commander Game Warden
Law Enforcement Division, Austin
Texas Parks and Wildlife Department