A Fish Eye View » fish

Eat fish and acidify the oceans

Mason Posner — Mon, 19 Jan 2009 04:10:01 +0000

When teaching marine biology I warn my students that if they are there to just learn about sharks and dolphins they will be sorely disappointed, because only microscopic plankton have the biomass to really affect the oceans. Being an ichthyologist this always hurt a bit. A recent paper in Science has restored my faith that all that microscopic stuff is just fish food – fish CAN change the world. Better yet, this story involves some animal comparative physiology.

First a little background on how we are killing our oceans. The same CO2 that is accumulating in the atmosphere from the combustion of fossil fuels and other sources, leading to global warming, is diffusing into the oceans and changing their pH. When CO2 reacts chemically with H2O, H+ ions are released making water more acidic. This declining pH is already adversely affecting marine organisms, which are often adapted to a narrow pH range. Calcium carbonate, however, can react with CO2 and limit the drop in pH. The production of calcium carbonate by microscopic organisms like coccolithophores is thought to be the major player in this regulation of ocean pH.

So where do the fish come in? Research on the toadfish, Opsanus beta, showed that this fish produces little calcium carbonate rocks in its digestive tract. Subsequent physiological research showed that the production of these “gut rocks” was involved in the absorption of water in the gut. Marine fish are less salty than the surrounding ocean. Water, therefore, diffuses out of the fish into their environment leaving them very thirsty. But when they drink they fill their guts with salty water, which would pull fluids from their bodies leaving them even thirstier. It is for a similar reason that you should not drink ocean water when stranded in a life raft (that’s when you drink your own urine instead). But the fish apparently have a trick. They accrete some of the salts in their urine as carbonate precipitates, lowering the salinity of the water in their gut and facilitating its absorption. And then the fish defecate the rocks.

Radiographic images of a live European flounder accumulating carbonate precipitates in its gut. The fish on top was living in freshwater and lacks "gut rocks". The same fish is shown below after only three hours in seawater. Note the opacities in the gut resulting from the accretion of carbonates (white arrows).

But would this calcium carbonate release affect the Ocean’s pH balance considering the relatively low biomass of fishes compared to plankters like the coccolithophores? In their paper Wilson et al. also calculate the total biomass of fishes in the Ocean and the amount of calcium carbonate they produce. While these types of calculations require a good number of assumptions, the authors claim that their conservative estimate is that fishes produce 3-15% of the Ocean’s calcium carbonate.

So next time PETA tries to convince you not to eat fish because they are cute, tell them a better reason is that fish poop could help save the marine ecosystem.

R. W. Wilson, F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, M. Grosell (2009). Contribution of Fish to the Marine Inorganic Carbon Cycle Science, 323 (5912), 359-362 DOI: 10.1126/science.1157972

Sea kittens . . . really?

Mason Posner — Thu, 15 Jan 2009 04:00:25 +0000

Next time you’re reeling in that fish, picture Whiskers or Fluffy hooked through the mouth on the end of your line. At least that is what PETA would like you to do. In a new PR campaign the animal rights group is attempting to rebrand “fish” as “sea kitten”. The rationale:

When your name can also be used as a verb that means driving a hook through your head, it’s time for a serious image makeover. And who could possibly want to put a hook through a sea kitten?

Point well taken. But I am not sure how I feel about my subject of study (I am an ichthyologist that does research on the fish eye) being renamed. PETA argues that:

People don’t seem to like fish. They’re slithery and slimy, and they have eyes on either side of their pointy little heads—which is weird, to say the least.

But I love fish, and I know legions of other ichthyologists that love fish too. And yes, I occasionally meet people, tell them I am an ichthyologist, then explain what that means, find out that they think that is cool, but am then asked: then you don’t eat fish, do you? But I also love eating fish, as do most ichthyologists I know. Is it weird to like eating the group that you study. I have a mycologist friend (studies fungi) who doesn’t like to eat mushrooms. But I think that’s an exception. And yes, many of you study organisms that you probably don’t want to eat. I am talking to you, entomologists and parasitologists. But I bet you malacologists out there love your oysters and scallops. Admit it, you ornithologists eat chicken.

While our love for eating fish, and the need for this important source of protein in the diets of many humans, is leading to the collapse of fisheries and marine ecosystems, making fish seem cute is not the solution. Ironically, the economic importance of fish and other marine organisms as food will play an important role in turning back the decay of our oceans, if that is possible. Whether it is restoration of the Chesapeake Bay to bring back the oysters and crabs, research in the Gulf of Mexico to maintain red snapper populations (check out that mahi my ichthyologist friend Will caught) or limits on trawling in the North Atlantic.

But I did have fun making my custom “sea kitten” (see the top of this post). Although it was labeled a flounder, but clearly has only one eye on the side of its head. What’s up with that?

The NPR story on the new PETA campaign attracted a money comment:

This story evokes a wonderful memory of a recent trip I had back to my mountain cabin. I had a nice hike and spotted a wonderful Sky Origami (falcon) crushing a Stuart Little (mouse) in its razor sharp talons. When I got back to the cabin I made sure the House Bunny (dog) was in so it wouldn’t get mauled by a Forest Angel (bear) that night.

Creepy Friday videos

Mason Posner — Sat, 10 Jan 2009 02:45:04 +0000

That is if you find spiders creepy. And if you do, maybe your fears are well founded.

This shark video is only creepy if you were in the submarine, and the sharks actually posed a threat. Which they probably didn’t. But it is still worth checking out.

Fish eyes do the coolest things

Mason Posner — Wed, 31 Dec 2008 19:14:41 +0000

Ed Yong over at Not Exactly Rocket Science beat me to the punch on this one. You should check out his summary of a new paper by a group of excellent fish eye people on the spookfish, Dolichopteryx longipes. Like many mesopelagic fishes that live in these low light conditions, the spookfish has tubular shaped eyes that look straight up to try and spot the shadows cast by soon to be prey items. This oddly shaped eye allows the fish to collect as much light as possible from above, but it does not allow the fish to see around or down. To do this some mesopelagic fishes have a secondary retina that looks laterally and ventrally, but this part of the eye does not use a lens to focus light. It was thought that the images produced by this secondary retina would be crude, but the new paper by Wagner et al. on the spookfish shows that instead of a lens, this species uses a reflective surface, yes a mirror, to focus light on its secondary retina. This is the first described example of a vertebrate eye that uses reflective optics to focus light, but may not be the last.

They don’t make shark cages like they used to

Mason Posner — Sun, 14 Dec 2008 04:27:50 +0000

The classic white shark strike from below is chilling to watch. What’s interesting is how the shark seems to accidentally crash into the cage, probably with its eyes rolled back after taking the bait. At that point it’s just trying to get away, leaving the divers to safely get out of the water. No crazed man-eater here, just a shark trying to eat and then freaking out after being trapped between steel bars.

Deep Sea News has critiqued this particular shark diving outfit’s operation for baiting the shark so close to the cage and for clearly bad cage design.