Eating shrimp (most especially the large tiger shrimp/prawn variety) is almost always a bad idea for a couple of reasons. One, it is bad for your health if the shrimp are farmed and this is especially the case if they are farmed in developing countries with lax regulations – think pesticides, antibiotics (most of the shrimp eaten in the US is imported). The second reason you should not eat shrimp is because it is bad for the environment. Farmed shrimp can lead to local degradation of the environment and farmed shrimp are often fed with fishmeal obtained by catching wild fish – this causes overfishing pressure of the so called “reduction fisheries” like sardine menhaden and other small fish species used to make fishmeal and fish oil. See this NY Times Article for more on the reduction fishery and its big impact on larger fish species and sea birds that rely on these small fish for their food source. Wild shrimp are mainly caught by bottom trawling methods and this method is among the most destructive of all fishing method currently in use. Bottom trawling scoops up all living organisms off the bottom just to catch a few shrimp. As much as 75% of the living biomass scooped up is not wanted and thrown back into the ocean dead as something called “bycatch”. A direct analogy would be if a deer hunter went into the forest and clear cut the entire forest of all trees and killed every living creature just to catch that one single deer! It is an absurd way of harvesting food from the ocean. Also, bottom trawling is done at gigantic corporate scales these days. The amount of ocean bottom trawled each year is 150 times the area of forest that is clear-cut on land each year. So bottom trawling is a big-big-big deal! Bottom line – don’t each shrimp (especially the larger tiger shrimp/prawns). See THIS ARTICLE for the full story.
Update: See Also THIS ARTICLE