Answer: Third option is correct.
Explanation:
Water conservation means use of little water and avoids wastage of water.
Water conservation at a fish farm is improved if we re circulate water in large scale fish tanks.
If water is replaced with fresh water every time, then it is wastage of water at a great amount.
So, if re circulate water in large scale in fish tanks it would help.
By doing this, our use of water is get limited and water would conserved.
Hence, Third option is correct.