I think your analysis is far to simple even if you are only considering energy cost and ignoring all sorts of other factors including those posted above. What about all the energy expended by those who collect the wild fish? What about all the energy it takes to transport fish from collectors to us? I'm not sure whether "tank raised" comes out ahead on energy or not -- in fact, it would be pretty hard to calculate.
You're correct, it takes a lot of energy to get a fish from SE Asia/Pacific to the US or wherever the fish is ending up. But it pales in comparison to the energy used to raise a fish from egg to sellable size. Figure at least 6 months (most likely almost a year) from egg to sellable. You not only have to supply water, heat, and light for those fry, but you have to supply food. You also have to supply water, heat, light for the live food to get those fry to grow, and for the phytoplankton to raise that live food. Aquaculture needs their own supplies, which most likely are not local and need to be shipped. Then, when you sell those fish, they are also going to be shipped, albeit a shorter distance, but still shipped nonetheless.
Don't get my wrong, I'm all for aquaculture, and it's really great if we can raise those species in bulk for food, but also rare species that we should leave in the ocean or species that can be trained to take frozen or dry food that otherwise would not. However, we should all be aware that many aquaculture methods are in no way good for the environment and that sustainable fishing is more friendly.
Here's a quickie for info from the Monterey Bay Aquarium's Seafood Watch (very reputable):
http://www.seafoodwatch.org/ocean-issues/fishing-and-farming-methods
While it's more for food fish, many issues also apply to the aquaculture of ornamental fish, which, while it represents a super small fraction of the aquaculture business, it directly uses knowledge from the food industry. I believe the most successful breeding of large angelfish is the P. maculosis angel, which while we keep in aquariums, is being cultured for food.
On the flip side, what about all the workers and divers and conservation effors that the *GOOD* collectors employ in their respective environments? If perhaps you pulled all those collectors out, then what would the local people then do? Would they fall back on destroying the reef to build homes and make a cheap buck? Would they have learned how to conserve their environment or would they keep trying to modernize and end up polluting? The list can go on and on for both sides of the argument, but it's not so black and white and fuel and electricity. Many of the good collectors put a lot back into the local economy and local population, and educate on conservation. This is very important if we want to conserve our reefs. The amount of collection for the marine ornamental industry is super small when compared to commercial fishing for food. That's the one we need to worry about.
As far as tank raised fish being more susceptible to disease, I've not heard this and I don't believe it to be true. Most people I think would say tank raised are hardier. I don't see all the designer clownfish being sick all the time.
