Barramundi switch genders midstream
"What's Australian seafood like?" a friend asked last week as we prepared to sail north along the Great Barrier Reef.
"It's good," I said. "My favorite is barramundi. It's an estuary fish found around here."
"What does it look like?"
"It's silver with a pointy snout."
That's all I knew, and we moved on to other subjects. But I've been short-changing my guests -- and myself -- with this bland description. These fish, I've learned, live remarkable lives.
Barramundi is a member of the perch family, a large and varied order containing more species than any other vertebrate group. Because this fish grows to 4 feet long, it was once called the giant perch or the giant sea perch.
Now, however, Australians use an aboriginal term for the fish, barramundi, meaning "bearing large scales."
The Japanese have a name for this fish, too: "akame." Besides north and northeast Australia, this fish is also native to the Japanese Sea, New Guinea, parts of India and southern China.
Barramundi never swim out to coral reefs. These are coastal fish that stick close to the rich waters of the estuaries.
It is in the estuaries that barramundi spawn between September and March on either a new or full moon, since this is when tides rise the highest. Each female lays several million eggs, which the tide distributes throughout the area.
The eggs hatch in 24 hours. Some baby barramundi develop in estuary mangrove forests, but many migrate upriver and spend their youth there.
Leaving the estuary for fresh water has its advantages. Fewer fish live in rivers than in the nutrient-rich estuaries, reducing competition for food. Also, it's easier to see and catch prey in clear river water rather than in the muddy, murky estuaries.
Another benefit in moving upstream is that fewer large predators live in the rivers than in the ocean. Although barramundi are in danger there from crocodiles, the nutrient-rich estuaries hold even more dangers. Sharks, saltwater crocs and other carnivorous fish patrol estuaries for prey.
Both juvenile and adult barramundi are themselves predators of fish. Young barramundi also eat insects. Adults, however, prefer shrimp with their fish.
Barramundi grow fast, reaching 8 inches long in 10 months, and 20 inches long in three years. At this time they all become sexually mature males.
The young males spend the next few years eating and fertilizing eggs. When the wild days of youth are over, at 6 years old, the males turn into females. All of them. No males exist after age 6.
Nearly all barramundi 4 feet and longer are females.
Mature females can grow to 6 feet and weigh up to 110 pounds. Their appearance is distinct, with large silver scales, a humped back and small glassy eyes.
Since barramundi are prized game fish and have a size-related sex ratio, the fishery is strictly controlled. Coastal mangrove swamps and wetlands are also protected to provide habitat for the young males.
An Australian fish book I have on the boat gives barramundi an edibility rating of four stars out of four.
The evening before my friends and I set sail for the barrier reef islands, I treated them to a barramundi dinner at the marina. We gave this fish four stars, too.