Q: Can you help me understand a sentence that the reviewer wants me to correct?

This is a very subject-specific question, I would not be able to comment on the meaning. I can only comment on the grammatical and stylistic aspects. Out of the three sentences mentioned in your question, only the first is clear and grammatically correct. The latter part of the second one is incorrect: "It has shown that it involves in physiological stress of zebrafish." It can be corrected to "It has been shown that it is involved in physiological stress of zebrafish." The phrase "it involves in" is awkward.  "Involves" is a transitive verb and therefore needs an object. However, the object is missing here. In addition to this problem, the third sentence also uses "This is shown." The simple present tense is not applicable here as this tense is generally used for things that happen regularly. But here, you are referring to an action that has just been completed; hence the present perfect tense "has been" is more appropriate.