By Nina Shen Rastogi

What’s the greenest way to keep a home aquarium? I love tropical fish, but I feel bad about running the filters and lights for so many hours.

I’ve always had a soft spot for aquariums. As a kid, I sat through a lot of long, boring dinner parties at Chinese restaurants, where the massive fish tanks were reliable sources of entertainment. But not all aquariums are created equal when it comes to sustainability. There are the energy concerns you cite, but where your fish come from is also a major issue, as is what you do with your pets at the end of your relationship.

Energy use for aquariums can vary widely, depending on your setup. According to a 1997 report from the Lawrence Berkeley National Laboratory, a small freshwater aquarium of, say, 10 gallons might use as little as 90 to 120 kilowatt-hours a year to run its lights, filters and aerators. That’s about as much as a typical coffeemaker uses in a year, hardly a major energy suck in the grand scheme of things.

As you go up in size, your electricity costs will naturally rise. A 55-gallon freshwater tank might use 280 to 400 kilowatt-hours annually. Adding a lot of plants increases your aquarium’s appetite, because you’ll need heavier-duty lighting to keep those plants alive. And generally speaking, saltwater tanks will use more energy than freshwater ones because of an increased need for pumps and powerheads to create water currents; marine aquariums can pull from 230 kilowatt-hours a year for a small tank to nearly 800 for a large tank.

Those big coral tanks I loved in my younger days at Hong Fu? They probably drew a whopping amount of energy: A 180-gallon reef tank requires upward of 6,000 kilowatt-hours a year. (Or at least it did 12 years ago.) With that kind of electricity use, you could power four or five refrigerators.

Since the Berkeley Lab report came out, there have been a few advances in aquarium equipment efficiency. You can shave off a few kilowatt-hours by using LED lights, for example, and there are newer, energy-saving pumps and ballasts on the market. One equipment salesperson I spoke with estimated that, overall, the amount of electricity aquariums use today might be about 25 percent lower than in 1997.

Aquarium keeping can also have hidden environmental costs upstream. In some parts of Southeast Asia, where the vast majority of the world’s saltwater “ornamental” organisms come from, fish are caught using squirt bottles filled with cyanide, which stuns the animals and makes them easier to extract from coral reefs. But the chemical can also damage the corals, as well as other organisms living in the reefs — not to mention weakening the fish so that fewer of them survive transport. (Keeping fish healthy isn’t just an animal-rights issue, after all; it’s also an ecological concern. The fewer animals that survive the process, the more intensive the harvesting has to be.) When buying wild-caught fish, look for those that have been captured with hand nets rather than chemicals.

Overfishing can be a concern with certain species, such as the Banggai cardinalfish. Found only in a few pockets off the coast of Indonesia, these silvery, black-striped fish have been labeled an endangered species by the International Union for Conservation of Nature, largely because of overzealous harvesting for the aquarium trade.

Sustainable collection is less of an issue with freshwater aquarium species, because 90 percent of them are farm-raised. (Saltwater fish are much harder to breed in captivity: As of six years ago, when the United Nations’ environmental office came out with an extensive report on the aquarium trade, less than 10 percent of marine ornamental species were capable of being farm-cultured.) Captive breeding helps reduce pressure on wild animal populations, but, as many conservationists argue, maintaining a sustainable trade in wild-caught organisms — both freshwater and marine — can be an environmentally friendly strategy as well, if it provides economic incentives for fishermen to keep their local ecosystems healthy.

Before you head to the pet store, then, do some homework to find out where your fish came from. If you’re lucky enough to live near one of the four Marine Aquarium Council-certified retailers in the United States (in Florida, Illinois, Michigan and New Jersey), you can buy saltwater fish that are verified to have been sustainably collected or cultured and then properly handled throughout the supply chain. (In the coming months, a new licensing program should increase the number of stores where you can buy MAC-approved fish.) You should also check out Reef Protection International’s Reef Fish Guide, which assesses popular marine species based on four criteria: survivability in home aquariums, abundance in the wild, availability and potential for captive breeding, and collection methods used. Local hobbyist groups can also be great sources of information and, occasionally, homebred pets.

Finally, if you have kids in the house, make sure they don’t harbor any “Finding Nemo” fantasies. Releasing nonnative species into the wild can cause all kinds of ecological problems, particularly if those species become established populations. If you find yourself needing to get rid of a pet fish, try to find it a new home or see whether a pet store will take it. If you must send your fish to sleep with its brothers, there are much more humane ways to euthanize your pet than dumping it in a pond or, God forbid, flushing it down a toilet.

Better yet, avoid getting yourself into that situation in the first place: Make sure you buy only fish that won’t get too big for your aquarium and won’t start turf wars with their tank mates. As with anything else you buy, the greenest fish is going to be the one you don’t have to replace.