Octopuses are tricky animals to keep in captivity. They're smart, strong and slinky. But surely their eggs much be easier—being naturally contained and all.
Not always, it turns out. Researchers in Chile have been on a quest to grow a local octopus species in captivity after it was overfished in the wild. The results of their efforts were published earlier this year in Aquaculture.
The meter-long Patagonian red octopus (Enteroctopus megalocyathus) is a slow grower. The eggs alone take five months of careful incubation and tending before hatching. And no one was sure the best way to keep these sensitive octo eggs alive. Previous attempts saw bacterial infections and failure of the embryos to develop at all.
The Patagonian red octopus is an important haul for Chilean fishermen, who catch thousands of metric tons of these animals each year. But in late 2008, the population of these octopuses appeared to be in serious decline. So the Chilean government banned their catch for three years. With the wild cephalopods unavailable, people pushed for more research into growing these octopuses efficiently in captivity.
So a team of researchers from Chile and Mexico went fishing.
The researchers captured 16 females and 12 males, who were then taken back to the lab and placed in individual tanks. The octopuses ate a diet of fresh crabs, fish and squid. The researchers allowed the octopuses to mate and then left the females alone again to lay and tend to their eggs—hoping to glean a few clues about embryonic development patterns and tending tips.
The females laid an average of 2,095 eggs each. The eggs began at just 10 millimeters long, and by the time the baby octopuses hatched, they themselves were closer to 14 millimeters long. Like so many animals, how well the baby octopuses developed depended both on the care the eggs received and the nutrition available to the embryos while they were still in the egg.
For all of our human failings at rearing baby octopuses, it turns out even the octopus mothers don't always get it right either. The researchers found that the females lost between 40 to 100 percent of their broods. In the first three months. (And these moms don't get a second shot. They die soon after their eggs hatch.) In fact, only about 15 percent of the eggs hatched. Many of the lost eggs were cleared away by the octopus mothers themselves. The researchers are still not sure whether that is similar to rates in the wild—due to infection or other contamination—or whether it was due to stress caused by the researchers' meddling.
Assessing the contents of the egg yolk sac during the embryo development, the researchers found that the octopuses used up just about all of the nutrients before hatching. In particular, unsaturated fatty acids seemed important to regulate membranes in the cold water environment. And, like developing human babies, the octopuses also had "a high demand for DHA to form a well-developed nervous system that ensures predatory skills of newly hatched individuals," the researchers noted in their paper. Of course, in the wild, almost all of the baby octopuses that did hatch would get eaten up by predators—or would fail to feed themselves enough to grow to maturity.
But the researchers are hoping to learn more from the octo moms to figure out how to keep the hatchlings alive and healthy, at least in captivity.
To read more about the finicky octopus, check out Octopus! The Most Mysterious Creature In the Sea.
Illustration courtesy of Ivan Phillipsen