Wild fish has largely been seen as `the best one can get' as they are expected to offer optimal nutritional quality and flavour, no risk of chemical contamination and certainly to be GMO free.  The reality is that taste trials comparing wild to farmed fish consistently reveal that panels are not able to distinguish between the two options.  Furthermore, nutritionists have shown that modern aquafeeds result in fish flesh that is as nutritious as the best natural products.
 
Consumer health is assumed to be assured when eating fish sourced from the wild, and I expect that this was true through history.  However, more recently, pollution of various sorts has compromised the healthiness of fish sourced from certain wild locations.  As many species are migratory, the level of certainty regarding their healthiness can be seriously compromised.  Farmed fish are maintained under managed conditions and can be reared without exposure to pollutants.  Although there is concern regarding the use of antibiotics and other therapeutics on farmed fish, the modern fish farm utilises very little, if any, chemicals or antibiotics, and if used, the standard approach is to select options that have a short half-life and are low risk.
 
Another form of pollution that is relevant, but this time aimed at the aquaculture industry, is genetic pollution.  Farmed fish are subjected to genetic improvement programs to select for desirable production characteristics such as rapid growth, disease resistance and high yield.  On the farm these traits are desirable, but when these fish escape they could breed with wild fish and alter the genetics of the natural stocks.  As it is impossible to improve on nature, any such change must be regarded as undesirable.  Fish farmers implement various strategies to reduce the escape of wild fish but certain infrastructure types, most especially cages, are not possible to secure with certainty.
 
The biggest factor in the debate is simply availability.  Yes, in the early days there were problems with aquaculture, as there probably were with any form of stock farming.  The Industry is cleaning up its act to minimise risk and impact on nature, and has advanced feed technology to ensure that the nutritional value of farmed fish is as high as it is in wild fish.  However, the relentless extraction of fish from every possible habitat in the wild has resulted in many stocks collapsing and others being close to the point of over exploitation.  We have reached or exceeded the maximum sustainable catch levels for virtually every stock and simply cannot harvest more from the wild.  By contrast, farmed fish production can easily be increased to meet growing demand.  In 2013 the mass of fish produced by aquaculture exceeded the wild catch for that year for the first time in history and the annual growth rate of aquaculture production is around 8% p.a.  As people realise that aquaculture actually is the greatest key we have to protect the remaining wild fish stocks, and as the virtues of farmed fish are becoming more widely known and accepted, greater support for the Industry is being obtained.  If we wish to continue eating fish we need to embrace aquaculture, and do so fast!
 
I recommend the following Ted Talk for those who wish to investigate this further.