Spawning and Parenting Behavior
of the Wolf Eel Blenny, Congrogadus Subducens
I remember the day that the little guy came into the LFS that I worked at. His attentive eyes and grim jaw peering out from behind the large stony coral in the tank immediately gained my attention. It was a pity that he was a saltwater fish, as I was only keeping freshwater tanks. I had, on several occasions, considered starting a saltwater aquarium, but eventually decided against it. The expenses, lack of space, and my complete lack of saltwater know-how all contributed to the decision, but most of all it was the feeling that any saltwater aquarium would have to be a show aquarium, and one of my favorite aspects of keeping fish is the behavior of breeding groups.
Anyway, back to the fish. The card underneath the obviously stressed little guy read GREEN WOLF EEL and below its name was a price, $26.99, just another reason not to get attached. Even with an employee discount it was still over $20, and that just wasn't in my price range. I had learned by now that buying unknown fish of that price was best left to the experts.
So I left the angry-looking, small critter in his cramped tank and went back to my duties as the fish guy. After 20-30 minutes I realized that the poor thing must be hungry, and, because one of my most exciting duties was feeding the carnivores, I decided to take a break from scrubbing and throw a feeder in. Wham! I was right about the thing being hungry, as the feeder hardly hit the surface before the eel snatched it right out of the water, and quickly wolfed it down in a mist of sand and scales. That had to have been one of the coolest carnivores I had seen in there, and I immediately threw in another feeder. The same process was repeated, about 12 times, until the little eel ignored further feeding attempts. I couldn't blame him though; the little guy's stomach had swollen to almost five times its size.
This relationship continued for quite a while, although in subdued quantities, he usually only took 1-3 fish, depending on the feeding frequency, which was usually about every day or two, if I had a day off. The eel seemed to be very hardy, and showed absolutely no signs of stress or illness, save the continuous, although subdued, laborious breathing I saw the first day. If the eel got stressed out a little more than usual, the breathing would become more protracted, and seldom disappeared altogether. The fact that it showed no signs of illness was impressive, since most of the saltwater fish that came in seldom went completely disease-free, and I never saw a single ich spot or cloudy eye on the little guy.
The only thing anyone could complain about was the color. The tag said "Green" Wolf Eel, and this fish was a light brownish color, with a white mottling of spots, and only a trace of green in the edges of its snout and fins.
He seemed perfectly healthy though, and after 3 months without being sold, I was attached to the little guy, despite my self-warnings. In this time, the eel had grown to almost double its overall size, and an additional 50% or so of its length, so after much deliberation, I decided that I would start up a saltwater tank after all, and would keep the eel as my cull fish, in place of the Oscar that had recently passed away.
I set up a twenty-gallon "high" tank, and though it may have seemed a little small to me, I reasoned that it was at least twice the room that he had been living with at the store, and so I set it up with one H.O.T. Magnum canister filter and a sponge filter powered by a Penguin 175 gph power head. The swirling water running over the pieces of hard coral and crushed coral sand seemed ready to be started, and, long story short (or at least shorter than I could have made it) I ended up with a small group of large, assorted, sailfin mollies, and was ready to add the eel.
After bringing the little guy home, and eventually releasing him into the new tank, he seemed noticeably perturbed, and sat glaring at me with his angry eyes and gaping mouth. I had grown accustomed to his sulking behavior after he had been moved to other tanks within the store, and so I left him to wallow within his own complaints.
When I checked the tank the next day, he was apparently happier, and seemed much more active than I had ever seen him in the store. This was encouraging, and Virgil, as I had named him, quickly polished off four fish.
This scenario continued for a few weeks, with the only differences being the occasional picking off of one of the smaller mollies (or the pretty little peppermint shrimp I had bought to help clean the tank) when I ran out of feeders for more than a day or two. This served as three lessons to me; feed plenty and often, refrain from adding small critters to the tank, and that fish are not the only feeders that could be used to feed him. I later found out that Virgil absolutely relished small crayfish, and I didn't mind the additional price for the occasional inclusion of variety, as I consider variety one of the most important aspects of feeding fish.
After about six weeks in the
tank, however, I was becoming worried. Over the past week or
so, the color (or lack thereof) issue had me thinking, and I
was afraid that Virgil might be suffering from a dietary or poison
problem, and the slowly distending belly didn't help my fears
at all. Over the course of a week or so, he had slowed his appetite
and for a good three days in a row he had not eaten anything
at all. His belly was very distended, and he even seemed to have
trouble balancing himself or fitting through the cracks between
the corals. Those of you who have read the title of this article
may be expecting what this was, but since I had no idea, I was
seriously considering a death in the future.
I was completely caught off
guard. My jaw literally dropped and I couldn't move for a good
five minutes. After I came to my senses, I realized that she
must be hungry, as she had not eaten anything in three days,
and had just lost a considerable amount of weight; the large
balloon of a belly she had gained over the last week was completely
gone, and she immediately ate eight feeders, periodically pausing
to circle her eggs and snap at the mollies who came too close
for here liking. Upon closer inspection of the eggs, I realized
that they were quite large, almost the size of frog eggs, and
were covered with uniform, white spots. Most of them were a salmon-pink
color, except for some totally white ones.
Regardless of the fertility of the eggs, much can still be ascertained from the behavior of the mother post-spawning, as she would most likely not know either. All of the spawnings have been placed in pits, and 3 of the 5 were placed in pits within rock caves. The mother excavates the pit with her tail. She coils around the eggs, makes a U shape, and quickly thrashes her tail in short, fluid movements to blow sand away from the nest site. I have witnessed this behavior only after the eggs have been laid, and intermittently whenever Verna decides the nest needs to be deeper.
In all but the latest spawning, which is only a day old as I write this, bits of broken coral and other bracken have been brought to the site by the mother's strong jaws, presumably to help prevent the mass of eggs from getting swirled away too far when the mother leaves for food or territorial reasons. If the nesting material is removed, it is then relocated by the mother and brought back to the site.
The mother's care instincts are very strong, and, even after having been separated from her spawn for over 12 hours, she returns to it as eagerly as if it were 12 seconds. This scenario occurred during the fourth spawning, which coincided with my moving of the entire tank setup into a 40 "breeder" tank with additional circulation, and an added protein skimmer. I had to separate the eggs in order to prevent them from being swept up by the two Penguin 1140 powerheads, as well as the drop off of parental interest after being moved into the new surroundings. Despite these interruptions, after the eggs were reintroduced the next day, she took right to them and continued their care until they, like the others, died.
Parental care is vigorous and constant. Aside from nest building behavior, Verna exhibits vigorous maintenance for her brood. The care behavior starts with Verna with her head to one side of the eggs. She then sweeps them inward while swimming in a circular motion until she makes one coil about the egg mass. Sometimes, while sweeping the eggs toward the inside of her coil, she uses her jaws very lightly to position the eggs. This is the U position that I mentioned earlier. The U position is the only method by which I have seen her hold her eggs, and she does this as much as possible, only stopping to eat or chase off potential threats. Even then, she will remain with her brood until the target has left her snapping range. When in this position, there are three major behaviors that I have witnessed. The first was mentioned before, which is the tail thrashing behavior used to excavate the nesting pit. The second, and most common, is a fanning motion, in which Verna, with her body wrapped around the eggs, fans them with her long, conjoined dorsal and caudal fins, presumably to help keep the eggs clean and aerated, much like the behavior of most surface or substrate spawning cichlids. The third, I assume, is in order to gain a better position around her eggs, and involves her swimming in a circle around the eggs for a few seconds, and finally settling in her U position and resuming her duties.
The mother exhibits a small amount of protection behavior, usually including, and almost never exceeding, a light nudge or push of the offender away from the nest with her jaws. This behavior is obviously discernable from eating behavior, and more closely resembles the aforementioned egg positioning behavior in actuality. I have never witnessed any injury caused by the mother during protective behavior, and only once saw anything more than a calm response to potential threats. This more aggressive protection occurred only once, and involved an overly ignorant, large, male fiddler crab that was too stupid to get out of the way, and continued to scuttle about the nest aimlessly. After a few gentle attempts, I saw Verna rear back into a strike position, very reminiscent to that of an angry serpent, and quickly lash out a few times at the crab before pushing him away from the nesting site. The small decapod was unhurt, and barely seemed to notice the skirmish that occurred.
I was lucky enough to actually witness the laying of the eggs for the fifth and latest spawn, and the activity was incredibly short-lived. The eggs were laid in one mass, in the exact shape of Verna's belly, which resembles a sausage shape. The entire process took less than five seconds. She was noticeably exhausted by the experience, and spent a good minute or so breathing laboriously in her usual stressed out manner, but after she recuperated she went right over to the eggs, and after about 24 hours they had been rolled into their normal, golf ball mass.
A few things that I have learned about the species during my research, which was surprisingly fruitless, was that Congrogadus subducens is not an eel at all, but rather a member of the blenny family, and goes by several names besides the Green Wolf Eel, including the Carpet Eel, Carpet Blenny, Wolf Eel Blenny, and Carpet Eel Blenny. The only information I could find on it was skeletal in nature, and consisted of the fact that it is a carnivore (duh) and comes from the Indian Ocean.
My own experiences, however, have taught me a great deal about the fish. The Wolf Eel Blenny is a fantastically resilient fish, and shows a remarkable amount of intelligence. Verna seems to recognize her tank mates from her feeders, and if an intended feeder is added to the tank, like for instance, the fiddler crabs, they will be ignored in favor of new additions. These she snaps up with relish, even if they are of similar kind or size, respectively. The only time that I have witnessed established inhabitants of the tank being eaten was when the eel was extremely hungry, usually due to a shortage of feeders at the LFS for up to three days. I don't think I have to mention it, but this fish does not appreciate missing a meal, and will let you know if it is hungry. I have heard from one person that these fish can be fed frozen food, but so far, I've had no luck with anything but live food, although a wide variety of fish and crustacean foods are all accepted greedily.
I have kept her as consistently as possible at 78 degrees Fahrenheit, and salinity of 1.024 to 1.025 in specific gravity, although the latest spawn has occurred at a temperature of 76 degrees Fahrenheit. With the lower temperature, I have noticed a less drastic growth of Verna's belly, and a seemingly more protracted gestation period, although the actual time between spawnings of 10 days was on the slightly longer side of average.
Verna's intelligence is even more apparent in her recognition of me. Her behavior toward me greatly resembles my experiences with Oscars and other relatively intelligent cichlids or catfish. She has even learned to respond to my feeding sign, in which I clasp a feeder in my hand (or not, she can't see through my hand) and make a fist. If I shake my hand a little, she immediately rushes over to that corner of the tank and begins looking quite attentively at it, until I drop the food into the tank.
The eggs, as of yet, have not hatched on any occasion. In the last four of five instances, the eggs eventually died off one by one until the number of dead, buoyant eggs was too great to be held down by the live, sinking ones. The mass then begins to float. Once the eggs are floating, the mother can no longer care for them, and they are removed until the rest of the eggs die off over the course of a couple days.
As I write this (February 17, 2002) Verna is now coiled around her fifth batch in the corner of her new 40 "breeder" tank, and, with any luck, this batch may hatch out. This tank has more room, better circulation, and an added protein skimmer, all of which may or may not contribute to a successful hatch out. Hopefully, some of the eggs will eventually hatch, and if they do, I will submit a follow-up article describing the post hatching care and growth of the fry.
Unfortunately, though I spent a whole roll of film on it, I only obtained the photograph pictured at the top of this article, which shows the U position clearly, but this is the first spawn, and the eggs are all pink, and not the normal purple that they have been in later spawnings. Hopefully, I will obtain some more photographs in the future, and if I do I will have them posted on the Internet version of this article. With any luck, I will be able to show some of the more exciting behaviors as well as some color shots of the eggs and spawning site.
Despite a few aforementioned
setbacks, I have witnessed some incredibly interesting spawning
habits and, despite her marine origin she still embodies everything
I love about freshwater fish. Completely aside from the spawning
behaviors, the Wolf Eel Blenny, Congrogadus subducens, is a perfect
first saltwater fish, and I would strongly recommend one for
anyone who wants an active, exciting, and intelligent inhabitant
for their marine aquarium.