This diary was originally posted to Daily Kos on September 6, 2006. Normal diary schedule should resume starting next week. Sorry for the absence this summer.
A while back I posted a diary on the American Eel. There is another species of eel on the New England shores that is less well known. The conger eel (Conger oceanicus) is rarely seen, even by the most dedicated fishermen. It is extremely shy, spending most of its time hiding out in caves or rock crevices. It is also strictly nocturnal, active only at night when it comes out to prey on fish and crustaceans.
Congers are true eels, having a continuous vertical fin. That is the dorsal, ventral and caudal (tail) fins are all joined with no breaks in between. And they get huge. An adult conger can reach a length of nine feet and weigh over a hundred pounds. It is perhaps the largest shallow water fish on our coasts.
Like most eels congers are scaleless, being instead covered with a thick layer of protective slime. If you've ever tried to hold an eel you'll remember that it is not an easy thing to do. Grabbing onto a large conger will likely result in having nothing in your hands but a big oozing mass of slime dripping between your fingers.
As mentioned, congers are nocturnal, finding their food at night using their very strong sense of smell. They feed mainly on fish (mostly daytime species which are defenseless and easily caught in the dark). They will also feed on crabs, shrimp and small mollusks. These eels often raid lobster pots, but are intelligent enough to escape before daybreak. Unless a lobsterman pulls his traps at night (a practice that is illegal), he will fail to capture this elusive fish.
The nostrils of this eel are protruding, rather than being set into pits as in most fish. This helps it find food in the cracks and crevices of the rocky bottoms. Congers have enormous appetites and grow very quickly. At one year it may already be over four feet long.
Photo by Donald Fairgray.
Like the American eel, congers have a very complex and unusual life history. Adults spawn after about fifteen years. Before spawning the eel makes a long migration hundreds of miles offshore. As they migrate the adults cease to eat and their bodies begin to change radically. The head changes shape, the teeth fall out and the bones turn into jelly. The male's eyes bulge to an enormous size. Once they reach the spawning grounds the eggs are laid and both parents die. A huge number of eggs are produced; up to five million for a single female. And in a gravid female the eggs may account for over a third of her body weight.
When these eggs hatch the young look like little transparent ribbons. This larval stage is called a leptocephalus larvae. The leptocephalus makes a journey of its own all the way back to the home coast of the parents. During the roughly two year trip the larvae slowly change form and after this metamorphosis become young eels (called elvers) at about four inches.
Leptocephalus larval stage.
Conger eels adapt extremely well to captivity, although they tend to be talented escape artists. Its slimy body can squeeze through a surprisingly small hole. They require a huge amount of food, although fortunately they are not picky eaters. Whole fish is best since the bones will give them plenty of calcium which is necessary for such a fast growing animal.
Despite their large size, I've found congers to be very docile, except with other congers. They leave all other fish (to big to swallow) alone, but as they grow they will not tolerate other congers. Interestingly, they do not fight during the day, but become very aggressive and territorial at night. These eels are long-lived even in captivity. However, as soon as the gonads begin to form they stop eating and soon die, even if they do not actually spawn.
And in captivity, when the fish decides it's time to migrate, you can forget about keeping them in their tanks. I've had some that literally beat themselves senseless against a weighted wooden cover as they tried to escape. When I see this behavior start I now simply release them back into the wild.
And just how tough are these fish? When I first started keeping them, back when I was skeptical of the Houdini-like behavior I read about, I came in one morning to find a dried up eel on the wood floor. Its slime coating acted like glue as it dried and picking the fish up made a sound like tearing open a four-foot long piece of velcro. Just before discarding the dried out animal I thought I sensed a muscle twitch. I washed him off and placed him back into his 600 gallon tank and few hours later it was swimming around (although pretty beaten up) as if nothing had happened.
Fun Fact: If you order "Anago" at a sushi bar, this is the animal you are eating.
Other diaries in this series can be found here.