I want to start a fish farm

This question is regularly posed so I thought it would be useful to address the considerations when narrowing down the options.
 
Why do you want to farm fish, or stated differently, what is the outcome you are looking for?
Some people want to farm fish because they enjoy working with, breeding or feeding the fish, or having pipes and pumps to monitor water flow.  If this is your intended outcome then it is important to recognise that profit is not your focus, and you can allow yourself the freedom of designing a system that is highly versatile, allowing for changes to be made as new ideas occur to you.
Most people wish to generate a margin from their fish farm with which to refund the initial investment, leaving a profit for the entrepreneur.  Identifying this clearly as a reason for the investment directs many of the decisions you will make thereafter, as economic viability is a central tenet.  I will assume a profit motive going forward.
 
Who is the market?
Before investing in infrastructure to produce fish it is vital to know who will buy the fish from you.  `Restaurants’ is not an acceptable answer; far more detail is required to ensure that you truly understand the market.  Which company, what form do they require the fish to be delivered in, what size fish are preferred, where will delivery be made, how frequently will orders be placed, what quantity of each product will they order each time and is there seasonality to their business that will impact orders to you?  Along with this you need to understand the legal requirements in terms of product health and safety, what certification is required for that market to purchase your products?
 
This is the stage that is usually neglected by want-to-be fish farmers; we are producers not marketers and therefore focus our efforts on what interests us most.  Beware of failing to understand and be guided by your market, there are many fish farm skeletons to bear testimony to the importance of thorough market analysis prior to investment.
 
What will you produce?
The outcome of the market assessment will be an understanding of which species and size you have a demand for, and what post-harvest value addition will be required.  These factors guide the development of your farm design and business plan.
 
Where will the facility be erected?
The market survey will inform you of where the product needs to be delivered, now you can decide where it makes logic sense to erect the infrastructure.  If you own land on which this is to be done, then fair and well, but hopefully you do not as this frees you to look for an ideal site that makes sense in terms of supplying to the market as well as meeting the Site Selection Criteria.  In addition, a site that offers some unique benefit such as a source of heated water, close proximity to a feed manufacturer or other strategic advantage can add a significant margin to every kilogram of fish produced.
 
Which infrastructure type will you use?
From the market research you will know which species to produce and where it is to be delivered.  This directs your choice of area where the infrastructure is to be erected, and therefore the climate where the fish will be farmed.  If the climate matches the optimal growth temperature of the species you wish to produce then earth ponds or cages can be considered, but if the climate is cooler than optimal by a few degrees for several months of the year then a recirculating system becomes the infrastructure of choice.
 
Rough Design
A rough design of the infrastructure can be done at this point to assess the area and water quantity required to run the production facility.  This will also indicate the quantity of power and feed required, and the number of staff.
 
Site Selection Criteria
At this point we can start looking for a site that meets all the criteria we established above.  Remember there are a host of points to weigh when considering a site in terms of its suitability to run a commercial fish farm.  Water quality and quantity are foremost, along with access space of an appropriate slope to erect the infrastructure.  The access road must allow for suitable sized trucks to pass in order to deliver feed and take marketable fish to your clients.  If there are buildings on site that can be used as feed stores, offices or a laboratory that is a cost saving and distinct advantage.
 
Design and Costing
Having identified the site we can now proceed to the full design and costing of the infrastructure.  This will optimise the utilisation of the site in terms of the positioning the farming components as well as the flow of processes and water.  At the end the investor will know what it will cost to erect and operate the business through the lowest point in the cash flow to the point of breakeven.
 
If you want to start a commercial fish farm, I encourage you to follow this path to ensure that you have the market, the site and the finances required to make a success of the investment of your resources.