Tag Archives: fish

Puffer fish armed with toxin in addition to its spiny body

Published October 5,, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott

A dead ulua, or jack, washed up on Kailua Beach recently after having tried to ingest a porcupine puffer fish, which inflated and stuck in its throat. ©Greg Turnbull

A dead ulua, or jack, washed up on Kailua Beach recently after having tried to ingest a porcupine puffer fish, which inflated and stuck in its throat. ©Greg Turnbull

Kailua resident Greg Turnbull sent a picture of a freshly dead, 36-inch-long fish he found on Kailua Beach during a recent dawn walk. Greg thought the fish was an ulua (jack), and I agree. Although it’s unusual for a big jack to wash up on an Oahu beach, that’s not what drove Greg to take the picture. The gaping ulua had an inflated porcupine puffer fish stuck in its throat.

The puffer fish made a fatal mistake. Swelling up in a predator’s throat is a good ploy to prevent being swallowed, but step two is crucial. The puffer must shrink and run before the suffocated fish washes ashore.

People call the 120 or so species of puffer fish several names — balloon fish, blowfish, globefish, toadfish — all referring to their famous defense: an elastic stomach. When threatened, a puffer engorges its stretchy stomach with water or, if a predator drives the puffer to the surface, air.

Susan holding a puffer fish. Courtesy Craig Thomas

Susan holding a puffer fish. Courtesy Craig Thomas

The idea is to grow too big for a predator’s mouth. If the pursuer has a really big mouth, the puffer sticks in the fish’s throat. Because fish breathe by taking water in the mouth and expelling it out the gills, a throat full of puffer fish is deadly.

Another deadly puffer defense is the ability to store a poison called tetrodotoxin. In the ocean, puffers eat plants and animals that contain naturally occurring bacteria that manufacture tetrodotoxin. By choosing food that doesn’t contain those bacteria, aquaculturists can raise poison-free puffer fish.

Tetrodotoxin is well known for being so potent that a tiny dose can kill a person in minutes. The poison blocks sodium channels in nerves, and when sodium can’t enter a nerve cell, it can’t tell muscles what to do, such as breathe. There’s no antidote to the toxin, but, because it wears off by itself, artificial breathing can save a victim.

Ulua (Jack). Courtesy Russell Gilbert

Ulua (Jack). Courtesy Russell Gilbert

So, I wondered, are jacks immune to tetrodotoxin?

Hard to say. Puffer fish have been found in tiger shark stomachs, and the Internet has pictures of a snapper, frogfish, loggerhead turtle and duck eating a puffer fish, but it’s unstated whether the animals lived or died. What I did learn, however, is that the sodium channels in some snails, crabs and presumably tiger sharks are unaffected by tetrodotoxin.

I also learned in my reading that 19th-century warriors from the Gilbert Islands (today Kiribati) wore what a British explorer in 1847 called “an extraordinary looking apology for a helmet.” The illustration shows a porcupine puffer fish skin on the head of a warrior. Apparently the man mistook a fish for a hat.

Thanks, Greg, for sharing your picture. It’s great food for thought.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2015 Susan Scott

 

Yellowstripe goatfish use spiky beard to detect prey

Published September 14, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser
©2015 Susan Scott

Weke are yellowstripe goatfish; when they are under 7 inches long, like the fish shown here, they’re oama. Courtesy Scott R. Davis

Weke are yellowstripe goatfish; when they are under 7 inches long,
like the fish shown here, they’re oama. Courtesy Scott R. Davis

At my favorite snorkeling spot recently, I found a line of anglers blocking my usual beach entrance. I hadn’t seen them there before but I recognized the scene. In August and September, it’s common around the islands to see men, women and children fishing near one another with short poles in knee-deep water, white buckets waiting on the beach. Years ago, I didn’t know what this configuration meant so I asked an angler who explained that they were fishing for oama.

“My wife fries them up,” he said. “Delicious.”

Besides being good eating, the man told me that some anglers use oama as bait for papio.

“What are oama?” I asked.

“Baby weke,” he said.

Papio are the young of members of the jack (ulua) family and weke are yellowstripe goatfish. When weke are under 7 inches long, they’re oama.

Ten species of goatfish of various Hawaiian names swim in Hawaii’s waters. All are bottomfish that cruise the ocean floor poking two stiff chin whiskers into the sand and sediment. When the fish finds a shrimp, crab, worm or snail, it shoves its snout in the sand to nab it.

Goatfish are experts at finding the goodies because taste buds cover the wiggly extensions, which apparently reminded someone of a goat’s beard. Jacks and wrasses sometimes take advantage of the goatfish’s hunting tools and tag along, hoping to filch a flushed prey.

Weke are familiar to us snorkelers because these 14-inch-long fish like to forage in shallow water. The buttery yellow stripe running down the cream-colored body makes yellowstripe goatfish hard to spot at first, but when hunting, the fish blow their cover. The busy whiskers, called barbels, leave puffs of sediment in their wake.

Male goatfish also flutter their barbels to court females. (Look! I can waggle my whiskers!) When not eating or dating, goatfish tuck their goatees out of sight under their chins.

Weke spawn at the edge of the reef and the resulting young hatch at sea. In late summer, the youngsters return to the reef, often hanging together by the hundreds.

Because I couldn’t politely get past the dozen or so oama fishers standing at my snorkeling spot, and didn’t want to risk getting hooked, I walked down the beach and entered there.

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And whoa! There beyond the sand, tucked into the corner of two coral heads, hung a thousand resting oama, maybe more. Their yellow-striped bodies shimmered in the morning sun and they moved in that beautiful fluid synchrony of schooling fish.

I hope they made a run for it.

DSCN1475_small


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2015 Susan Scott

 

Scientific name for fish doesn’t quite do it justice

Published April 13, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott
Plover

Dascyllus albisella, or, in Hawaiian, aloiloi. ©2015 Susan Scott

While snorkeling last week, I noticed that some Hawaiian dascyllus were mostly gray, some were nearly all white, and further on, they were black with a white spot on each side.

The name Hawaiian dascyllus doesn’t tell you what kind of marine animal I’m talking about, and even if you know Greek, you still don’t get much of a clue. The generic term dascyllus (da-SILL-us) means “a kind of fish.” And the species name of the Hawaiian dascyllus, albisella, is equally nondescript. It means “white.”

Even though I see different colors and patterns in this fish, I know it’s the same species because Hawaii has only one dascyllus. (Eight others occur in the Indian and Pacific oceans.) But the distribution of black, white and gray in individuals varies widely.

The Hawaiian dascyllus, sometimes called the Hawaiian domino damselfish (more descriptive but a mouthful), reminds me of a fish-shaped beverage coaster. The flat, roundish species grows to 5 inches long.

fish

Juvenile dascyllus usually hover in schools just above branching corals, but long-spined sea urchins and crown-of-thorns starfish are also favorite hangouts. At the approach of a predator (or snorkeler), the babies dive to safety inside the coral’s narrow corridors or among the urchin’s or starfish’s sharp toxic spines.

Some adult dascyllus spend their entire lives in the arms of antler coral, venturing out to graze on passing plankton. Other adults throw caution to the current and live in the open, using cracks and crevices in nearby rocks and reefs as emergency shelter.

The juvenile Hawaiian dascyllus is black with a brilliant white patch on each side and a neon-blue spot on the forehead. As the fish gets bigger, it loses the headlight and its white side spots fade.

dascyllus

As an adult, the Hawaiian dascyllus changes patterns to suit the occasion. When courting, the fish’s sides turn bright white, while the head, fins and tail are all black.

Dining calls for different attire. When feeding, the fish’s sides are white, but the edges of the scales there darken, giving the fish a gray mesh look, as if it’s wearing a shirt of chain mail.

When threatened, adult dascyllus revert to their juvenile colors of all black with bright white side spots.

After reading up on dascyllus colors, I went back to my snorkeling site to match patterns with behaviors, but I couldn’t tell what those perky little fish were up to. All I knew as I watched them dart here and there in their assorted black-and-white outfits was that the ancient Hawaiians had it right when they named the fish “aloi­loi.” It means “bright and sparkling.”

fish


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2015 Susan Scott

 

Fish reproduction an intriguing process

Published September 1, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

In 1958 my mother went into labor during a Labor Day picnic. The pandemonium that ensued, ending with the delivery of a healthy baby boy, made such an impression on my 10-year-old mind that since then I’ve linked Labor Day with the labor of giving birth.

Today, given my interest in marine life, I’ve extended that link to include the birth of fish.

Fish don’t deliver live babies in the way of us mammals (sharks and seahorses being exceptions), but in a massive ocean teeming with predators, fish have methods of producing offspring that are a category of labor all its own.

The most common kind of fish reproduction is called broadcast spawning, a system in which males and females release sperm and eggs into the water. And that’s the end of it for the potential parents. Spew and split. Job done.

The chances of free-floating eggs and swimming sperm connecting on a coral reef is small, and offshore even smaller. But fish have ways of upping the odds. One is to produce an enormous number of eggs and sperm. This is where labor comes in. When it’s time, as dictated by moon phase, day length, water temperature or something we don’t know, female reef fish produce tens of thousands of eggs and males manufacture millions of sperm.

Open ocean species churn out even more.

The queen of egg production is the ocean sunfish (scientific name Mola mola, hence the common name, mola). In one 4.5 foot-long female, researchers found an estimated 300 million eggs in her one ovary, several orders of magnitude greater than the average broadcast spawner. Since molas grow to about 6 feet long, it’s likely that a full grown female would have even more eggs.

Broadcast spawners’ tiny floating eggs and sperm become part of the drifting plant and animal soup known as plankton, the beginning of the food web. Plankton eaters gobble up most of those sex cells, but some fulfill their destiny of continuing of the species.

Researchers measure a fish’s reproductive effort by comparing the size of its gonads to the size of its body. Charles Darwin proposed the idea that because fish ovaries are considerably larger (30 to 70 percent of the female’s weight) than testes (5 to 12 percent of body weight), female fish invest more energy in reproduction than males.

Today, however, males get more credit. Because random spilling of sperm is a waste, males expend considerable energy to attracting females, establishing territories and running off trespassers.

Some male fish send out pheromones that cue a female to begin egg maturation. Others signal their fitness by turning bright colors or performing lively dances. And when the going gets tough, the tough change sex. Wrasses, parrotfish and anemonefish change sex as circumstances demand.

Studies show that larger female fish of all species produce more and bigger eggs, resulting in higher offspring survival.

That’s why it’s crucial in this era of depleted fish stocks to leave some of the biggest fish in the ocean.

Most people don’t associate Labor Day with reproduction like I do. But in nature, it’s the only labor that counts.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2014 Susan Scott