Sorry I have no clue how to help here, but I bet lots of MS appraisers could offer some insight. MS is the self-proclaimed catfish capital of the world. They hatch em, raise em, and sell em. Mighty tasty I might add.
I’ve only ever seen one appraisal for a fish farm. Is it just a hatchery for game fish or for raising tropical fish, or edible fish such as tilapia or cat fish? This type of appraisal requires a going-concern valuation, including the allocation of equipment, stock and intangible assets. You’ll need to research the business of fish-raising, markets for various types of fish, the types of fish that can be raised at your subject facility, obsolescence of existing equipment from technological obsolescence, etc. Good luck with that one.