The world population is growing at an unprecedented rate and a major stable food source in the form of fish has been overharvested to the point that the supply from wild stocks is now diminishing.  Aquaculture, the farming of fish and other aquatic organisms, is the only reliable way in which we can meet the growing demand for fish.
 
Commercial aquaculture has been around for several decades, but only since the 1960s has production really increased rapidly.  Prior to this the oceans, rivers and lakes across the globe could provide sufficient food to feed people.  As the world population grew so did the pace at which we harvested fish from the wild, until in the 1990s we saw the capture fishery figures stagnating.  This occurred due to fishing pressure exceeding natural replacement rate, causing many stocks to crash to below the point of economic extinction.  Whilst the problem is easy to solve, simply stop fishing until stocks have recovered, this is not going to happen in a world where so many are dependent on fish for part or the bulk of their protein requirement.
 
Aquaculture has grown in response to the rising demand for seafood products coupled with the stagnating supply from wild harvests.  The Industry expands at an annual compounded rate of around 8.3%, and current production levels are flirting with 100 million tons p.a.  In 2013 the production from aquaculture exceeded the output from capture fisheries. 

Aquaculture has other more subtle advantages as well, including that it employs people in the rural areas, whereby working against the global problem of urban migration.  The Industry, with the exception of pond farming, is also a non-consumptive water user and the enriched effluent water is well suited to being used for crop farming.  Aquaponics is the ultimate expression of this, where the fish waste fertilises the growth of plants within the same system, purifying the water for the fish and resulting in 0% waste.
 
There has never been a better time to start your fish farm; the demand for many species is high and growing, and there are good options for profit.  However, as with any business, make sure you do your homework carefully and invest appropriately to ensure you have the best chance of success.