Originally Posted by Cutar
Oh lol I already knew thatt. Which is why I was planning to do one red tailed shark, two dwarf gouramis, and maybe 2 other fish, a snail, and a shrimp
The minimum tank sizes mean the fish needs that tank practically from the first. Now, it is possible to temporarily keep such a fish in a smaller tank, but this is only temporary for several reasons.
First, fish grow throughout their lives, unlike humans. As it grows externally, it is also developing internally. If the surrounding water is not sufficient, the internal development can be deformed, what is called "stunting," and the fish will have endless health issues and proably early death. It is not fair to the fish to subject it to this.
Second, fish "personalities" are affected by their environment. Recent scientific studies have now confirmed what many of us have believed for years on this issue. Tank size--both the physical dimensions but also the water conditions due to those dimensions--affect the fish psychologically. Aggression is often much greater as a result. And this means the fish is stressed out by its lack of adequate "space", so it literally "takes it out" on the tank. Similar to you being locked in a small room permanently with no means of escape. That is what you do to the fish.
So, "temporary" means very limited time before the fish is placed in a suitably-sized tank so that it can properly develop and be normal and have a healthy, normal life. I would therefore not even consider such a potentially-large fish for a 20g unless you have a 4-foot tank ready. And by the way, a shrimp would not last with a shark in the same tank.