More on the experiment done in the ECOLAB. The results indicate that hatching does not depend in a simple and obvious manner on the temperature pattern. What the data do suggest is that the proportion of alevins which swim well and which are still alive after two weeks is largest, when water is added at the lowest temperature in the cycle, so that it increases steadily for 12 hours after wetting.
Last week, at the ECOTRON Ile de France research station, five students, one engineer and myself did a short experiment on hatching Austrolebias. We used a prototype of the ECOLAB developed there, to simulate a diurnal cycle with a ten degree temperature difference between night and day (going from 15 to 25 degrees). At four times during the cycle, we put embryos in the ECOLAB in multiwell plates and added 5 ml of “hatching water” to each well. We used about 400 embryos from several species.
The data will be analysed next Tuesday, but my first impression was that we had the least bellysliders when the embryos were wetted at 15 degrees, and the temperature went up to 20 degrees within the following six hours.
The ECOLAB consumes lots of energy and resources, so let’s hope our results pay off, that the outcome will make all our hatching more efficient. More on this next week.
This Monday, I’ve starting hatching fry, at a modest scale. Usually, that requires some preparation, Artemia nauplia need to be available when the fry hatch, since these definitely want to eat straight away. Since it is still cold outside, hatching the Artemia would require a heated space. Later, from May on, they can just be hatched outside, in a flat tupper with no aeration. I decided to circumvent that for the moment.
So what I got is a lot of small Cyclops and other small pond food and I now raise the fry on that. Using nets of different mesh sizes, I selected only the smallest invertebrates. I also carefully avoid to feed Chaoborus larvae. Last year I experienced that these are very fond of killifish alevins and manage to kill them all. Last year also, I managed to raise fry exclusively on pond food very well. So all the energy that took, was me some minutes scooping food and sieving it. No heating, no salt water, no aeration. And an extra bonus: I had to add food to the fry just once or twice a week and did not have to remove leftover Artemia.
The amount of fry is still modest, but there are alevins swimming of Austrolebias toba, arachan “Arroyo Chuy” and vazferreirai “Parque Rivera”.
My three A. elongatus which were outdoor didn’t make it through the frost.
Looking at the survivors of the cold period in January-February, it seems that the survivors are restricted to part of the Austrolebias phylogeny I made based on molecular data. This part includes some relatively large species. The amount of data is, of course, almost negligible, so this is just an impression leading to a new hypothesis:
Large size in Austrolebias might be in some cases an adaptation to cold environments.
How to avoid tanks from freezing over in case they have to be left in the garden? The Build it Solar website lists many examples of solar heaters and other DIY projects. Particularly inspiring examples are the Solar Horse Tanks.
On the other hand, inside a wooden barn which is a bit better isolated than most greenhouses, it is maybe sufficient to have a large water mass for heat storage, for example by stacking a number of plastic tanks with water in a spot which receives much sunlight during the day, not too far from the tanks with fish.
Should be ready by next winter…
Europe is suffering under a cold spell. Austrolebias don’t necessarily die when it freezes. I’ve filled a small greenhouse with 90 liter tanks, some containing few old fish bred in 2010 and early in 2011. These fish are too old and too large to transport to a different site and have already survived a cold spell outdoors, with 3 cm of ice on their tanks. They are otherwise healthy. I want to give them a chance to reproduce in spring and therefore decided not to disturb them nor euthanize them.
In the greenhouse, during the night, tanks have so far frozen over with ice of about 1 cm thick. Since cold weather usually means sunshine, the greenhouse heats up during the day, removing the ice cover again and allowing the fish to breathe well. The total amount of water in the greenhouse is large, about 400 liter. I hope everything goes well, but there is a risk of failure. Then I will need to invent a better system in order to protect my old fish; or move or euthanize them all before winter.