A 400-million-year-old penislike piece of anatomy strengthens the argument that ancient armored fish were engaging in surprisingly modern internal fertilization.

Earlier this year researchers discovered that a group of extinct fish—known as placoderms—had been giving birth to live offspring an astonishing 380 million years ago. And live birth can only mean one thing: eggs must have been fertilized within the female’s body. But how? The team was stumped by a lack hard evidence of a crucial piece of male anatomy.

But a paper, published today in Nature, reports the discovery of a 400-million-year-old bony protrusion that could have made the live birth possible (Scientific American is part of the Nature Publishing Group).

Just when you thought you’d heard it all about the effects of greenhouse gases, researchers have found that higher atmospheric carbon dioxide levels could lead to changes in fish anatomy involved in navigation.

A study of white sea bass eggs and larvae showed that the developing fish grew larger ear bones (otoliths, which don't field sound, but rather help fish sense speed and direction) under higher CO2 concentrations. The results appear in the latest issue of Science.

The researchers raised the fish at different CO2 saturations and then examined their otoliths under scanning electron microscopes. The find may spell trouble for fish down the road. It also highlights the unpredictable nature of biological changes in CO2-rich waters, as they had expected the ear bones to shrink rather than grow.

Is your local river among those flowing merrily along, or is its health threatened by development plans? A conservation group has issued a new report ranking the 10 rivers most at risk this year of becoming flooded or their habitats threatened because of industrial activity.

American Rivers, a Washington. D.C.–based organization, ranked the rivers based not on how polluted they are, but whether they're imminently threatened by development plans, mines or dams.

Topping the list is the Sacramento–San Joaquin river system, which flows from the eastern Pacific Coast Ranges to the western Sierra Nevada before emptying into California's San Francisco Bay. The group warns that a levee failure there could jeopardize the water supply of the 25 million people who depend on it (by making the water too salty to drink). In addition, it says that pumps that feed the water supply have reversed the rivers' natural flow, causing fish populations to decline.

Officials in coastal states are worried that the high  upkeep of boats in the depressed economy has mariners literally abandoning their ships in droves — a practice that could threaten the environment.

There's no official tally of cast-off boats, but  an unusually high number are reportedly being dumped in waters off the coasts of Florida, South Carolina and Washington State; California is mulling a measure that would let owners surrender their vessels to the state, according to the New York Times. Other media reported last summer that more than 200 boats had been left in New York's Jamaica Bay. "Our waters have become dumping grounds," Major Paul Ouellette of the Florida Fish and Wildlife Conservation Commission told the Times. "It's got to the point where something has to be done."

A 300 million-year-old fossilized fish brain was discovered during a routine computed tomography (CT) scan, according to a study published today in the Proceedings of the National Academy of Sciences. Until now, scientists assumed that brains rarely—if ever—turned into fossils. Other soft tissue fossils, such as muscles and kidneys, have been found that date back longer than 350 million years ago, but because the brain is delicate and consists mostly of water, it's much less likely to be preserved in fossil form, says study co-author John Maisey, a curator in the paleontology division of the American Museum of Natural History in New York.  But "It's more than just a curiosity," he says. "Modern technology has revealed a fossil that we really didn't know about before." High-powered scans using x-ray synchrotron microtomography (which, like a CT, uses x-rays to image cross-sections of an object) allowed scientists to peer into the rock-solid skull to see the 0.06-by-0.28-inch (1.5 by 7 mm) brain.

We wouldn’t mind swimmin' with these fishes.

Check out Histiophryne psychedelica, a new species named for its crazy tan and peach stripes, and lackadaisical style of getting around the seafloor, which resembles hopping more than swimming. The fish is described in this month's issue of the journal Copeia.

No other fish is known to "hop," study co-author Ted Pietsch, a curator of fish at the University of Washington's Burke Museum of Natural History and Culture, said in a statement. Divers first spotted the fish in January 2008 in the harbor of Ambon Island, Indonesia.

Scientists in Australia are looking at fish larvae there as if they have two heads—because they do.

Millions of larvae in the country’s Noosa River were found to have grown two noggins, and chemicals from a nearby macadamia nut farm may be to blame for the defect.

"Fish don't have two heads, they generally have one,” Acting Premier Paul Lucas tells today’s edition of The Australian newspaper. “Let's find out why that is the case.”

One of two commonly used farming chemicals—the insecticide endosulfan or the fungicide carbendazim—may have caused their disfiguration, according to the Courier Mail. The chemicals could have ended up in the river through spraying or runoff, Matt Landos, a lecturer in aquatic animal health at the University of Sydney, told the newspaper. The Noosa River is in the southeast section of the state of Queensland, which spans the northeast quadrant of Australia.

The striped bass population in San Francisco Bay has been plummeting since the 1970s and now scientists know why: fish moms are passing down damaging pollutants in the water to their young, according to a new study published today in the Proceedings of the National Academy of Sciences. Researchers say the findings may pave the way for stiff new regulations on the chemical culprits.

Striped bass and other fish have been dying in droves off the coast of San Francisco for decades; pollution from industry and agricultural runoff has long been blamed.

What exactly makes a fish organic? Apparently, one that feeds on a nonorganic diet.

A U.S. Department of Agriculture (USDA) advisory panel says that producers should be allowed to slap organic labels on farmed fish even if their diets include wild fish and other feed that isn’t organic itself—definitions that environmentalists say depart from the criteria for other certified organic animal food products.

The labeling criteria, approved yesterday by the National Organic Standards Board (NOSB), an advisory panel to the USDA's Agricultural Marketing Service, allows up to a quarter of farmed fish feed to consist of wild fish, though not from endangered species. "There's no time table," for when the agency will take up the recommendations, Joan Shaffer, a spokeswoman for the service, told ScienificAmerican.com today. "We'll review it as soon as we can." 

An Atlantic blacktip shark spontaneously reproduced without the company of a mate, scientists report in the second documented case of the phenomenon.

Five-foot-long (1.5-meter) Tidbit, the ironically named resident of the Virginia Aquarium & Marine Science Center in Virginia Beach, Va., spawned on her own — no male assistance involved, according to Reuters. Sadly, Tidbit died in May 2007 during a veterinary checkup, before birthing her until-then unknown 10-inch-long shark pup. The case is published in the new issue of the Journal of Fish Biology.

Scientists last year wrote about an asexual hammerhead shark that reproduced on its own, a process called parthenogenesis in which unfertilized eggs divide. Bony fish, reptiles, birds, lizards and Komodo dragons also can reproduce asexually.