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.
“A case for sympatric speciation by cannibalism in South-American annual killifish (Austrolebias)”
We demonstrate that large Austrolebias evolved at least three times from small ones. For one case, we argue that piscivory evolved starting from the evolution of cannibalism on conspecifics.
Yesterday I colllected Austrolebias wolterstorffi (Velasquez) eggs. I just decided to make some pictures of them, using a DinoLite USB microscope with UV (395nm) and near IR (940nm) leds. Here are the results on a fresh egg (well maybe not from the last few days) that I just put straight from the peat onto a piece of paper on my desk. The result is simple to achieve and really encouraging. So I will try to get pictures of all main developmental stages with this lighting. Left: UV; Right: IR.
A small A. prognathus (Salamanca), some ten days old. I have been worrying about controlling nitrate and levels of other waste products in my tanks, to maximize juvenile growth of small ambitious fish like this. In some places the tap water is really excellent, in others it’s barely acceptable which makes the level of difficulty to maintain some species very variable. I also start believing that local tap water properties really determine how many people engage in the aquarium hobby and also determine the fish species that do well and are maintained in the killifish community. Wouldn’t it be nice if we could make some things “easy” anywhere?
In many situations, replacing water when it’s almost too late can help of course, but I prefer to be ahead of things, to avoid excessive levels to build up or to “clean” the tap water. So I am moving away from tanks with just some peat on the bottom, and I add zeolite now, just a little, to see how it behaves, what the effects are and if it might help to make raising fish easier everywhere. Plans are to measure lots of tanks and different waste product treatments later, in a situation where I start from dechlorinated tap water. Will be some work: all samples will have to be filtered and frozen before they can all be analysed together.
After some serious thinking I decided to try a heating mat and a controller, to store my killifish eggs at a more or less fixed temperature at home. It didn’t work. The fluctuations in temperature right above the mat for example went from 24 to 36 degrees, when I just wanted 22 C… So now I’m back to a system where some tanks with an aquarium heater are standing amidst the boxes with peat. Should work, has done so for years.
I’m in Paris and the weather is great. For Austrolebias, it is important to avoid that the tanks heat up too much. In the past, I experimented with netting, different depths and different tank colours, all with some effects, and it is time to start planning ahead for this year.
Two ideas are under consideration. The first is putting tanks in a mesh tunnel, which provides ventilation and shade. The second idea in the pipeline is to copy a phenomenon which occurs in the field. There the water is often murky due to suspended clay particles. This provides a great experience: when it’s very hot and you step into a pond, at moderate depths your feet will be standing in fresh and cool water! The fish are there as well. So I’m going to buy a block of clay in a craft store and will turn some tanks murky this summer.
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”.