The author spears her first lionfish in Placencia, Belize. Lionfish are an invasive species to the area. (Steve Hay)

Sinking slowly through Belize’s turquoise sea, Giovanni Gonzalez has murder on his mind. The dive guide scans the reef, his dreadlocks moving like a sea creature. I see only the usual confetti of tropical fish, but I can tell that Gio has spotted a lionfish tucked into the coral.

He readies his spear, takes aim and fires. The impaled fish materializes in a cloud of silt, thrashing to free itself — or at least sink a poison-barbed fin into someone’s skin. No fool, Gio pulls out a pair of scissors and disarms the fish by snipping off its spiky fins. A squeamish vegetarian, I turn away and watch the fins drift like feathers toward the ocean floor.

Details, Belize

(Gene Thorp/The Washington Post)

Gio is clearly having a lot of fun, but he’s also ridding the reef of a dangerous invader. Native to the Indian and Pacific oceans, lionfish were released into the Atlantic in the 1980s — most likely by Florida aquarium owners who tired of feeding the voracious creatures. Since then, these orange-and red-striped devils have colonized coastal waters from Rhode Island to South America, devastating local fish populations wherever they go.

In Belize, they’re making a meal of the tropical fish that tourists like me fly hundreds of miles to see. So, to protect the marine ecosystem and their own livelihoods, fishermen and dive professionals began hunting lionfish in 2002, Gio tells me once we’re back on the boat. “There was a bounty then,” he says. “Fifty dollars a fish.” Even with a price on their heads, the lionfish continued their invasion. “We need tourists to spear lionfish, and we really need people to start eating them,” Gio says.

When I’d booked my ticket to Belize, hunting and eating poisonous fish hadn’t been on the top of my to-do list. My plan was to laze around on a quiet beach with a frozen drink and take a leisurely look at the undersea scenery. Topside in Belize, I found plenty of laid-back charm. But beneath the ocean’s surface, I discovered a world of fearsome creatures engaged in a fierce battle for survival — and I got pulled into the melee myself.

Swimming with sharks

My home base for the week, Placencia, is a charming fishing village three hours from the capital, Belize City. Soon after arriving, my travel companion and I discover that the town’s real main street isn’t the recently paved road, but a narrow sidewalk that sets off near the public beach, wanders past sparsely populated cafes, and barges right through people’s back yards. In the afternoon heat, we see only a smattering of sunburned tourists on the sidewalk, but as the sun sets, the town’s melange of residents gathers to loiter and gossip.

After failed attempts at eavesdropping — most Placencians speak Kriol, a musical mix of English, West African and Native American languages — we gravitate to the friendly buzz at the Barefoot Bar, a brightly painted pavilion where several patrons are, in fact, barefoot, and at least one appears to be sharing a drink with his pet iguana.

After a long day of traveling, I want to spend the next day exploring no farther than the 10 feet between my beach bungalow and the sea. Fate, however, has other plans. Whale sharks are migrating down the coast, and we can’t miss the opportunity to see the biggest fish in the sea.

Though these behemoths can grow to 40 feet long, they strike terror only in the hearts of the krill and the other tiny ocean creatures they capture in their gaping maws. So tourists flock to Placencia every spring to swim with them, and we just happen to be in the right place at the right time.

Or so I’m told. After an early wake-up call followed by a half-hour of diving in open ocean, our only company is a sortie of snorkelers getting knocked around by waves at the surface.

I climb back on the boat, disappointed. But just as I peel off my wetsuit, someone starts shouting. “Get in the water! Get in the water now!”

I grab my fins and someone else’s mask, jump off the side of the boat and almost land on a whale shark the size of a school bus. His dappled gray back is just inches from my nose, and I can see that the spots, which I expected to be white, are actually a delicate pale yellow. Definitely worth the sleep deprivation, I think, as the shark returns to the inky depths.

The opportunity to swim with whale sharks may become increasingly rare, as overfishing in Asia landed them on the World Conservation Union’s “vulnerable” to extinction list in 2000. Human competition for snapper and other game fish, which the whale sharks eat as spawn, may further deplete the sharks’ numbers, scientists say.

If humans can start using our appetite for seafood for good, by avoiding overfished species and eating invasive ones, we can help whale sharks and the other colorful reef fish that make Belize diving such a spectacular experience. So when Gio invites me to join him on a lionfish hunt, I say yes.

‘The lion slayer’

It’s my third day in Belize, and I’m speeding toward a lionfish stronghold called South Water Caye. I woke up early, set on spearing a lionfish and saving thousands of juvenile reef fish from untimely deaths, but my lionfish-hunting resolve wanes as Gio shows me his scars.

“Here’s where the spine went all the way through my hand,” Gio says, pointing to the slack skin between his thumb and forefinger. “I got stung twice here,” he adds, as he shows me a white mark on his knuckle.

While rarely fatal, lionfish stings are intensely painful. “It’s two hours of the worst pain I’ve ever felt,” Gio says.

I turn over the stumpy, blunt spear in my hands as Gio gives me further instruction. If you skewer a lionfish through the side, he might swim up the spear and stab your hand. “Try to hit them right between the eyes,” he says.

As I step off the dive boat, I consider my list of reasons for backing out of the lionfish hunt: poor vision, bad hand-eye coordination, a dislike of intense pain, an overdeveloped sense of empathy that keeps me from squishing even roaches. However, as a member of the most invasive species of all, I decide that it’s my duty to at least try to spear a lion.

The reef comes into view, and it’s not long before I spot my prey, his hiding place given away by a single feathery fin. Ready, aim, fire! The fish and I are equally surprised when I sink a spear right in the center of his zebra-striped head.

My courage tapped, I hand my spear to Gio, who removes the fish and adds it to a string. The day’s kills, about a half-dozen fish, trail behind us like a balloon as we swim toward the boat. We pass a pair of fairy basslets, one of the lionfish’s favorite snacks. “You’re welcome,” I tell them, telepathically.

Back at the dock, Gio cleans my fish, and I take it to the chef at my hotel. “Can you cook this?” I ask. It’s not uncommon for guests to bring their own fish to dinner, the cook says, but my lionfish is a first.

That night, other diners are intrigued by my special order. “What does it taste like?” asks a fellow diver. I take a nibble of the flaky, pale flesh and admit that I’ve been a vegetarian since age 6.

Since I have no idea what fish is supposed to taste like, I divvy up the fillet and share it with anyone who wants to try. “It’s good,” says a dark-haired woman at the bar. “It’s light, but it has some toothiness to it, like swordfish.”

For the remainder of my vacation, I do nothing braver than rescue a drowning drink-umbrella from the swimming pool. Still, whenever I venture into the hotel restaurant, diners and waiters hail me as “the lion slayer.”

If the critters ever show up in the Potomac, they’d better watch out. Forget about the fillets; I’m in it for the glory.

Details, Belize

Dingfelder is a travel, humor and science writer. Follow her on Twitter at @SadieDing.