Obviously captive bred fish is the way forward. Currently with what's happening to the seas and reefs I think it's so wrong to plunder at will. In terms of what's worse freshwater or marine it has to be marine. A lot of freshwater fish might live in a stream or a river but they probably explore little of it for fear of being eaten or swimming into a unknown fishes territory. So it's more acceptable to house them in an aquarium compared to a porcupine puffer that naturally has a whole reef and the sea to explore. We can't recreate that. I think the minimum tank size for a porcupine a something like 450L. It should be double that. It's very prejudice of me but freshwater wild caught fish doesn't bother me that much since it doesn't have as greater a knock on effect like collections from the ocean do.
As a more marine based keeper I'd just like to add a reply. The seas aren't plundered, well not for aquarium fish. All fish removed are controlled by quotas and unlike in the freshwater hobby, threatened species are not touched. There has not been a species (apart from possibly the bangaii cardinal which is nearly always captive bred now) threatened by the aquarium trade in the wild (and that species is still allowed by cities) but I can think of a few in freshwater such as the red tail shark or denison barb.
Freshwater fish explore just as much of the water as marine species if you compare like for like. A porcupine puffer explores a large territory but so does the mbu puffer. You have more cryptic species in rivers but you find these as well on the reef, like damsels (perhaps the cichlids of the sea) who live by one coral head their whole life after they have settled on the reef.
Predators live in both areas so I don't see a difference there to be honest nor do I see a difference with fish in unsuitable tanks, for your porcupine puffer I could suggest a giant gourami, Oscar or dozens of other species.
You could argue that rivers are more of a problem than seas for pollution or over harvesting. The marine hobby is actually very well managed for the most part. The Hawaiian fishery is one of the best understood and the science has show that fish populations have been improving due to their management. Unfortunately human politics has got in the way and aquarium collection was recently banned, after the science was ignore. However collection for food is still allowed even though the aquarium collection was negligible in comparison.
Fuji also imposed a ban of the collection of corals and invertebrates from their waters at Christmas but after the science was presented showing the beneficial work the aquarium trade was having, rebuilding reefs and conserving these areas, they reversed the ban and support the main company Walt Smith.
It has also been shown that by harvesting wild animals you preserve the area by giving it value. For a reef, if you stop collection there is no ongoing economic value but keep collecting and you won't see dynamite fishing or removal of live rock for house or road building.
Marine fish aquaculture is still a pretty small part of the industry. I would always advocate the support of it if possible but it's an expensive and high energy alternative. I've bred quite a few marine species and it's very time intensive, energy intensive and expensive. Unfortunately there also seems to be a move towards the guppification of marines for profit. We see this with clownfish where longfin (not great for a species who aren't the best swimmers to begin with that come from a very high flow environment) or stubby versions have been bred. I know people love variations but their are always tradeoffs.
I try to buy captive bred whenever possible but sometimes breeders standards aren't particularly high and you run into deformed fish. I've lost count of the number of fish with one eye, lost or twisted pectorals or jaw abnormalities. Some of these might make a fish more interesting, like nemo's little fin, but often at the detriment to health.
Captive fish are often bolder, have less disease issues (or at least simpler diseases to treat) and are used to aquarium life. That makes things simpler for us and shouldn't be overlooked.
