Cities: Skylines

When you begin in the fishing industry, place you Fishing Harbour and Fish Farm in a good location with good export routes. Be warned, these will generate a lot of cargo traffic!

The Fish Farm will farm and yield fish within a confined space, whereas the Fishing Harbour will send boats out to catch fish along a route that you designate. Use both so that you can try to unlock Aquaculture and Fisher King simultaneously.

When you draw your fishing boat routes, you will notice colours in the water. The different colours in the water represent the different types of fish. Whilst the Fishing Harbour will catch fish from all of these types, the yield will be low.

To increase your yield, use the specialised fishing harbours as you unlock them. The yield on these is far superior and will help you work towards this achievement quicker, but make sure that the majority of the line that you draw to send those boats out match that of the fish type, since they will not catch other fish types along their route (if you 'follow' your boat, the description will read 'crusing').

Also, as you unlock the other fish farms (algae and seaweed) place these down too to better increase your city-wide product amount and help work towards this achievement quicker.

Edit (27th April): It turns out that you can track how much fish/plant-based products have been caught/farmed by checking the individual buildings. Thanks to S P 4 C E Y for this information.