While cleaning tanks with fry, I discovered this egg raft, probably from a Chaoborus phantom midge. The mother has emerged in the fish tank, and laid her eggs on the surface.
I don’t know if it is very easy to spot, but on this photograph an egg with a developed embryo. You can see its right eye and it’s an Austrolebias charrua (“Canal Andreoni”) from peat collected in June 2018. Particular about this embryo is that it overwintered without heating, in a box with peat standing next to the cold tanks. It has been at temperatures as low as 4C, maybe even 2C. I will try to convince it to hatch in April, when night temperatures in the garden house rise above 10C.
Things break down. Fortunately, this type of small incubator usually does so in the same way: its Peltier element that cools and heats dies. The repair costs a few euros and takes less than an hour. So by now, the incubator is filled again with eggs of several killifish species and fry in their first week after hatching. As it is springtime, I am germinating chillies in it too.
This is how I grow fish at home during winter. They are hatched in a small Peltier incubator, and kept in there for a few days with Artemia as the main feed.
After that they are transferred to relatively flat boxes with tap water, rain water and java moss. The food then becomes a mix of Artemia, Daphnia, copepods and tubifex or blackworm. Great at that point is that mortality can be almost avoided completely if the tanks are not crowded. You should count an Austrolebias alevin from a small species per 150 square centimeter tank surface. For large species, count two to three times that surface.
At these low densities, the fish will grow to maturity without problem. In the stack: Cynopoecilus melanotaenia (Paso del Dragon), Austrolebias charrua (Canal Andreoni), Austrolebias patriciae (Cruce Ferrocaril), Austrolebias vandenbergi (Talon Cansado), Austrolebias reicherti (Paso del Dragon), Austrolebias luteoflammulatus (Ruta 15km7.5, Canal Andreoni), Austrolebias gymnoventris (Velasquez).
Inside the wooden house, there is still fry approaching maturity. They were born a few weeks ago and have been fed once with Artemia, after that with pond invertebrates. Now they will need to overwinter at relatively small sizes and without heating. Critical to make this work seems to be using tanks with a large surface and low depth and to have sufficient thermal mass in the house. When I see a plastic box in a shop, I get the feeling I can predict how many I can raise in there to maturity, just by looking at the surface area. Maybe it’s time now to start experiments on density-dependent growth and survival in my fish.
In the house I also store orchids (Zygopetalum), palm trees (Archontophoenix) and citrus (Yuzu, finger lime) during winter and cuttings of Physalis Peruvian groundcherry.
A simple trick which seems to work to attract a lot of Culex mosquitos to a tank so that you can feed killifish fry with their larvae developing from the eggs they lay in there, of any age you might need:
Add a small amount of wheat flour and yeast to the (dechlorinated) water of a 80L basin partly shaded. If the mosquitos are around, soon you will even smell how many they are in there. The flour was my idea, the yeast Milan‘s.
I didn’t expect her to be still alive but here she is. A female A. wolterstorffi (Velasquez) that overwintered at temperatures going as low as 4C. A pair of the same population managed to lay eggs all through winter. I lost them in March when the water started warming and I just hatched about fifty of their alevins yesterday.
May and June are for hatching alevins and raising them. I’ve noticed that I keep on getting the same numbers of juveniles for each tank size or type. There are some species effects of course but things are rather predictable, as if their populations are regulated. So I can more or less calculate how much fish I can breed like this per year. The alevins are hatched with rain water after storage at home for at least five months. Then they are fed Artemia once, and a mix of zooplankton after that. I tend to keep them inside for the first two weeks, but I’m thinking of changing that, because I have bigger tanks outside. This is of course not what you should do when you have for example only two alevins of a precious species to save your population. Then put them next to your bed.
There are these embryos that are refusing to hatch. Here such an environmental change denier and an alevin that did hatch (A. elongatus “Gral Conesa”). Our main explanation is that the non-hatcher will do so at another occasion and is just hedging its bets. However, here the hatched alevin suggests another explanation: it is infected by fungus. The unhatched embryo might suffer the same infection, preventing it from continuing the life history while being eaten alive.