What are the black spots on stingrays?

“I was at the aquarium and I noticed that the stingrays all had patterns of black specks on their backs. Was something wrong with them?”

After doing some research, we found that there was probably nothing wrong with the stingrays. Most likely, our patron was seeing the rays’ ampullae of Lorenzini, special sensory organs shared by sharks, skates, and rays. The ampullae are pores leading to jelly-filled canals that end in nerve endings, and they can act as electroreceptors, sensing the electrical pulses given off by the muscle activity of other creatures.They can also detect changes in temperature and water pressure. If our patron had looked closely at the underside of the ray, they would have seen many more ampullae, most clustered around its mouth. These help the rays find food on the sea floor.

The ampullae were first discovered by Marcello Malpighi in 1663, but were not described in detail until 1678. Stefano Lorenzini was the first to describe them, which is why they’re named after him. Though scientists were aware of the ampullae, they did not understand their purpose until the 1960s.

We found our information in Michele Debczak’s article “10 Stunning Facts about Stingrays” on Mental Floss, Barbara E. Wueringer and Ian R. Tibbetts’ research paper comparing the ampullary systems of shovelnose rays in Reviews in Fish Biology and Fisheries, The Encyclopedia of Sharks by Steve and Jane Parker, and Sharks: Ancient Predators in a Modern Sea by Salvador Jorgensen.

Why are my fish disappearing?

One of our patrons was concerned about their home aquarium. They had maintained it for many years, but their older fish were starting to die off. They had started to add new fish, but a few of those fish had disappeared. Was one of the older fish eating them? Was something wrong with the environment?

Assuming that the tank was tightly covered, the water was clean, pH balanced, free of harmful chemicals, and an appropriate temperature, and the fish were not being under- or over-fed, we checked Mary Bailey and Peter Burgess’s Tropical Fishlopaedia, Maddy and Mic Hargrove’s Freshwater Aquariums for Dummies, Dick Mills’s Aquarium Fish, Stuart Thraves’s Setting Up a Tropical Aquarium Week-by-Week, John Davies’s Complete Encyclopedia of the Freshwater Aquarium, and www.aquariumcarebasics.com for more information.

Our patron’s aquarium included a Buenos Aires tetra, a rainbow shark, and a rosy barb. They had been attempting to add an otocinclus catfish and a few varieties of platys and tetras.

According to Bailey and Burgess, an omnivorous fish who has never bothered its old tankmates may go after small new fish. If it came into the aquarium at the same time as the old fish, or if it was too small to eat them when they were added, the omnivore seems to recognize them as companions and not food. It’s used to food coming from above – which is also where new fish are introduced. Platys, tetras, and barbs are omnivores, and Thraves mentions that it’s common for larger fish to pick off neon tetras, so that could be a problem. While our patron’s fish are generally known to be peaceful, Buenos Aires tetras can get aggressive as they age, especially the larger ones. Rainbow sharks (which are not actual sharks but are closely related to barbs and danios) are also somewhat aggressive and territorial, especially toward their own kind. Only one should be kept in an aquarium and it should be given plenty of places to hide. (The Buenos Aires tetra and the rosy barb, on the other hand, are schooling fish and are happiest in groups of at least six.)

It’s also possible that the fish were simply unhealthy when our patron purchased them, or that they didn’t take well to the stress of transport, depending on how long they lasted. The otocinclus catfish in particular is known to be delicate and often has trouble acclimating to a new environment.

If our patron is still worried about their fish, Tropical Fishlopaedia and Freshwater Aquariums for Dummies both have information on troubleshooting aquarium problems.

Are eels nocturnal?

One of our patrons was reading George R.R. Martin’s A Song of Ice and Fire fantasy series, on which the HBO television series Game of Thrones is based. Presumably to give things a more fantastical flavor, Martin made up his own system of telling time, having characters refer to times such as “the hour of the bat,” “the hour of the wolf,” and “the hour of the eel.” “I understand the wolf and the bat,” our patron said, “because they’re both associated with night. But why the eel? Are they nocturnal?”

While we can’t explain why Martin makes the writing decisions he does, we could find information about eels. We looked them up first in the World Book Encyclopedia. It didn’t tell us anything about when they were active, but we did learn that they undergo several metamorphoses over the course of their lives. American and European eels travel to the Sargasso Sea to lay their eggs. The eggs hatch into transparent larvae shaped like willow leaves. The larvae change into small transparent eels, called glass eels. By the time they reach the coast, the small eels have developed a greenish-brown color. No longer baby glass eels, they’re now juvenile eels, called elvers. The elvers travel inland and grow into yellow eels (though they’re more yellow-green or yellow-brown). During this stage, which can last many years, they reach their full size, three to five feet for females and around one-and-a-half to three feet for males. Eventually, they reach sexual maturity and turn black and silver. Now, they’re called silver eels. They fatten up for their journey back to the Sargasso Sea to mate. (They don’t eat on their voyage, and their digestive system actually starts to break down.) After mating, they die. Because they are born in the ocean, grow up in fresh water, and then go back to the ocean to spawn, eels are catadromous, and they’re the only such fish in North America.

As interesting as this is, it didn’t answer our question. We found that information on the U.S. Fish and Wildlife Service website. Freshwater eels are indeed nocturnal, at least during their yellow phase. They come out at night to eat crabs, fish, insects, eggs, clams, and frogs. They have small teeth and weak jaws, so to break off pieces of food that’s too big to swallow whole, they’ll grip it in their mouths and spin their bodies. They can spin up to fourteen times a second, almost three times as fast as an Olympic ice skater. Eels can move just as well forward and backward, and they can move over land through wet grass and mud because they’re able to absorb oxygen through their skin.

For more information on eels, James Prosek’s fascinating Eels: An Exploration, from New Zealand to the Sargasso, of the World’s Most Mysterious Fish is available through CLEVNET. George R.R. Martin’s books that inspired this question (as well as the television series inspired by the books) are both available at the Newton Falls Public Library or through CLEVNET.

How Long Do Bluegill Live?

“I stocked my pond with bluegill a few years ago and I’d like to know how long they live.” 

Our extensive collection of gardening books at the Newton Falls Public Library includes several on water gardening, such as Helen Nash’s The Pond Doctor, Richard Bird’s Water Gardens, and Peter Robinson’s Complete Guide to Water Gardening. However, these books all dealt more with the ornamental kinds of fish such as goldfish and koi. We couldn’t find any mention of bluegill in David Alderton’s Encyclopedia of Aquarium and Pond Fish either.

Fortunately, searching online brought up the answer. According to the BioKIDS website (which is run by the University of Michigan), bluegill typically live from four to six years in the wild, although in captivity they can get to be as old as eleven.

For more information on enjoying a pond, including tips, lore, and recipes for fish, frogs, and crawdads, Louise Riotte’s Catfish Ponds & Lily Pads is available for borrowing.

Will My Fish Die If I Carry Them Through the Security Gates?

“I had never heard this before, but someone I know was purchasing a fish at Wal-Mart and the cashier told her that the security gates would cause the fish to die. It was suggested that she lift it over her head while walking through.” While the fish in the patron’s story survived she and the Newton Falls Public Library wondered if it has that ever happened.

The HeraldTimesOnline Bloomington, Indiana [www.heraldtimesonline.com/stories/2010/05/31/digitalcity.058553.sto] addressed this very question in Rebecca M.Troyer’s article, Hotline favorites: Can I eat my Crocs? Exploding fish at Wal-Mart? “Lift up your fish through ye mighty gates” (March 25, 2009). The Hotline investigated by contacting Wal-Mart and the scanner manufacturer. Both corporations reported that there had been no “documented instances” or reported problems in relationship to the health and well being of fish. We informed our patron that this seemed to be well researched and it appeared to be safe to carry a fish through security and out of the store.

Urban legends such as these are good for storytelling. As our patron enjoyed this tale, we directed them to library materials with additional amazing stories, such as Alligators in the Sewer: and 222 other urban legends by Thomas J. Craughwell, Spiders in the Hairdo: modern urban legends collected and retold by David Holt & Bill Mooney, Too Good to be True: the colossal book of urban legends by Jan Harold Brunvand, Urban Legends: the as-complete-as-one-could-be guide to modern myths by N.E. Genge and the DVD MythBusters. Mega movie myths.