A pond or a lake is still a pond or a lake. Are you really comparing a lake to an aquarium? A good example of stunting due to environment sizes can be seen in koi and peacock bass. When kep in small garden ponds or aquariums, they never reach a fraction of their potential sizes. Koi can easily reach 3ft in a few years given a good sized pond. But when kept in small ponds 1-2,000g they're basically runts. Why? Same with peacock bass kept in 200-400g tanks vs those kept in 5-10,000g tanks.
And this because of lack of food? Please.
IMO your completely wrong bro. Seems like your stuck on the idea that fish don't outgrow fishtanks. We'll leave it at that i guess
To the OP...Gd luck with your clown loaches. They're awesome fish, just feed them plenty of protein along with plenty of WC's and they will be just fine.