How about this.
We've got an exhibit with two full sized Amazon wolf fish (Hoplias malabaricus). (i work at the Shedd aquarium) Previously, no insitution that we know of has been able to house two full sized individuals. Because of some dimorphisms we noted, we speculated that we had a pair. They always stayed near eachother.
They normally spend all their time very close to the water surface. They stay motionless in some of the habitat we've got set up. One summer, they started acting a bit strange. For several weeks, I observed them resting on the bottom. Usually one at a time, but occasionally both. I started getting worried when I noticed some differences in coloration. They were exhibiting really dark coloration...nearly black. And both of them were now resting on the bottom. They hadn't been eating well for weeks, and had gone off food for almost a week.
One day I noted a large pile of eggs underneath the large of the two individuals (I suspect its the female) I immediatly recognized a very large spawn. The eggs were quite large, approximately 3-4mm in diameter...mustard yellow in coloration. The eggs were mounded up in the shape of a gumdrop, about 6 inches high. A few days later, the eggs disappeared, but the pair stayed on the bottom. Even though they were far in the back corner of the exhibit, I could tell that they were floating over a small depression in the sand.
I went in on SCUBA later in the week to do some routine cleaning. I visited the nest...ever so carefully. This is when I noticed hundreds of the fry. I decided to net some out, fearing that the fry would never survive on exhibit.
I pulled approximately a hundred fry, approximately 10-20% of the spawn. The fry grew very quickly on brine shrimp nauplii and moina. Soon, it became quite clear that they were canibalizing each other. We continued to feed aggressively with increasingly larger food items (bloodworms to fry less than 1/2 inch), but could not stop the canibalism. Soon we had 50, then 25, then 10, then 2, and now just one is left.
The parents continued to guard the "nest" for a period of at least 4 months. They fed intermittently, but both continued to lose weight. Eventually, each of them visited the surface, and fed with the other fish. They continued to spend more and more time at the surface...ie normal behavior. Subsequent SCUBA dives was unable to confirm the fate of the fry on exhibit.
This was easily 8 months ago. Recently I was informed by another diver that there are several 2-3inch wolf fish swimming around in the debris at the bottom of the exhibit. We also still have the individual from the fry I netted. He as reached nearly 5 inches.
