How many fish can you see in a fish tank at most?

Textbooks are very inaccurate and dogmatic. What he said is the absolute situation, which is the goldfish bowl of the questioner's house. The refraction of light may be different because of different fish tanks, even different thicknesses, or it may cause many afterimages because the production can not reach the theory. Think about the kaleidoscope. What will happen if you make a similar fish tank with an outer wall? This kind of question will only limit people's thinking.