Tag Archives: wrasse

Nonprofit’s scientific news is a salve for a gloomy world

Published August 27, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott

The Society for Science and the Public, a nonprofit organization dedicated to sharing scientific news, emails me with weekly updates. As I scroll through the headlines, I’m amazed at the scope of human curiosity and people’s creativity in gaining knowledge, from finding exoplanets to editing genes.

I can spend hours at this well-written site, but before I lose myself in the DNA of Darwin’s dogs or how neuroscientists view “Donkey Kong,” I check out the latest in the marine world. One study that caught my attention was about the Taser-packing fish, the electric eel.

Before I even read the study, I wondered how this eel, scientific name Electrophorus electricus, is related to the moray eels we know so well here in Hawaii.

They’re not. The electric eel isn’t an eel at all. It’s a member of a fish family called knifefish, native to South American lakes and rivers.

The 6-foot-long electric eel delivers up to 600 volts to kill its prey. For those of us who’ve been accidentally shocked by a 110-volt household outlet — or worse, the 220 volts used in other countries — 600 volts is a mind-blowing jolt. Evolution made sure that the eel got its meal.

In waters where electric eels go hunting, other fish lie low, staying motionless behind rocks and among plants. Given such hiding, plus the fact that the electric eel’s vision is poor and the rivers are murky, a biologist at Nashville’s Vanderbilt University wondered how the eel finds its prey.

The researcher discovered that as the eel swims it shoots out tiny electric currents that cause a hiding fish’s muscles to twitch. And that’s all it takes. The eel heads toward the twitcher, shocks and eats.

Another fishy headline read, “Female fish have a fail-safe for surprise sperm attacks.” After a female ocellated wrasse (a Mediterranean species) chooses a mate, the couple make their nest. But bachelor wrasses lurk nearby, waiting for the female to lay her eggs. The rascal then dashes in and floods them with sperm. A Yale biologist discovered, however, that the female wrasse’s ovaries coat the eggs with a fluid that favors fast-swimming sperm. Because mated males have speedier sperm, the female’s chosen mate wins the race to the egg.

Sometimes I get so discouraged by the stream of terrible news throughout the world that I wonder whether our species is doomed. But then I get these science emails and life looks much better. T.H. White explained my feeling in a favorite book, “The Once and Future King”:

“‘The best thing for being sad,’ replied Merlin … ‘is to learn something. … Learn why the world wags and what wags it. That is the only thing which the mind can never exhaust, never alienate, never be tortured by, never fear or distrust, and never dream of regretting.’”

For a learning lift, visit www.societyforscience.org.

Labor’s reward found in offspring, one or many

Published September 1, 1997 in the “Ocean Watch” column, Honolulu Star-Advertiser ©1997 Susan Scott

My longtime readers may remember my story about a Labor Day many years ago when my mother gave birth to my baby brother. The event was such a sensation in my 11-year-old mind that, since then, Labor Day has had a double meaning to me.

Besides commemorating workers, the day also honors those who perform the supreme labor: that of perpetuating life on Earth.

In the world of fish, this labor comes in many forms, ranging from the release of eggs and sperm into open water and leaving the rest to nature, to the provision of nutrients to embryos developing inside a female fish’s body.

Tunas are typical of the first hit-and-miss type of reproduction. These schooling fish spawn in the warm upper layer of the open ocean. Each female tuna releases about 50,000 floating eggs per pound of body weight, and each male releases millions of sperm in the vicinity. The eggs that get fertilized hatch in about 30 hours.

It’s a lonely, perilous world these youngsters face. When the tiny tuna, only 0.1 inch long, begins its life in the marine world of fish-eat-fish, its parents are long gone. The mortality rate is staggering.

Although not many tuna hatchlings make it to maturity, not many have to. Of the millions, only two need to reach adulthood to keep the tuna population stable.

This type of reproduction may seem easy on the parents, but the cost is high.

Producing millions of eggs and sperm at each spawning requires tremendous amounts of energy.

At the opposite extreme are sharks, which produce fewer eggs and less sperm but use considerable energy giving their offspring a head start.

All sharks have internal fertilization, meaning the males deliver sperm directly inside the female through extensions of their pelvic fins. In many species, the female retains her eggs inside her body until they hatch, then gives birth.

Some kinds of sharks, such as sand tigers, threshers, makos and maybe great white sharks, have a unique way of nourishing their unborn pups.

One embryo remains in the mother’s body, eating its later-arriving siblings. The young of these sharks have the advantage of entering the world already fairly large.

Most sharks found in Hawaii have a more familiar way of feeding their unborn babies. A tube, called a pseudo-umbilicus, connects each embryo to the mother’s tissue. When the embryos are large enough to survive, the little sharks are born.

Between these extreme reproductive labors lie variations as vast as the ocean itself:

 Flying fish lay eggs bearing sticky threads that attach to floating seaweed. This natural cover likely gives hatchlings more protection than they have simply floating free in the open ocean.

 Pipefish and seahorses are a human female fantasy. In these fish, it is the males who become pregnant. The female deposits her eggs into the male’s stomach pouch, then takes off. The distended male incubates the eggs for 10 to 50 days, after which his tiny babies pop out.

In seahorses, the youngsters immediately head to the surface for a gulp of air, which helps them swim upright.

 Cardinalfish are also a female dream-come-true as far as the work goes. During the spawning season, females lay masses of eggs. Males fertilize them, then collect them in their mouths, holding them until they hatch. Sometimes the males’ mouths are so full of eggs, they can’t close their jaws completely.

 Then there are the female wrasses and parrotfish that get tired of all that egg-laying and simply turn into males. Many wrasse species spawn in groups, releasing eggs and sperm in a rapid upward rush. I’ve watched this happening and it looks like pure fish ecstasy. Procreative labor does have its rewards.