Odontesthes regia

Hannes returns to the US, but the experiment continues!

Posted on November 9, 2025November 9, 2025 by Hannes Baumann

10 November 2025. The spring is now in full swing here in Dichato, and the days are getting steadily hotter and drier. The past 6 weeks flew by in a whirlwind of action, and with all the last minute preparation plus the vagaries of coordinated field sampling and larval rearing it definitely is with a little pride that I look back at all that we have accomplished in this short time.

We stood up the experimental setup in just a matter of days, with new tanks and in a new (better) location inside the main wet lab of the Dichato station (aka 'El Acuario'). We flew to Iquique for the October full moon and were rewarded with spawning ripe fish; and with similar ease sampled the Dichato population just two days later. A trip to the notoriously difficult Coquimbo region unfortunately ended without fish, but the sampling of the southernmost population in Puerto Montt was again timed almost perfectly for the November full moon.

All the while the setup withstood the reality test, and I taught Tamara Cuevas, a technician from the station, the many aspects large and small of the rearing methods. Tamara will now take over the daily rearing for one month, before I will return in mid December to help terminate the experiment and then take home all samples. All the best, Tamara, for your time as the main experimenter!

We are halfway through the rearing, fingers crossed that the second half will go as smoothly!

The Chilean silverside experiment begins to produce data!

Posted on October 29, 2025October 29, 2025 by Hannes Baumann

29 October 2025. While the fish from Dichato in the coldest treatment have just begun to hatch, their conspecifics from Iquique and Dichato growing at the warmest temperatures have already more than doubled their size at hatch and are therefore ready for a first length sample. This is always a particularly sweet and rewarding moment, when after all the work to get to this point - it now finally arrived.

In each rearing container, 80 fish remain to grow further, while the rest is sampled, preserved in ethanol and then measured via calibrated pictures. Then the size difference between hatch and the first time point is divided by the number of days to obtain our first growth rate estimates of the second experiment!

DI14-hatchday_5 — On 29 October, the embryos from Dichato are about to hatch in the 14C treatment

No luck in Caleta Sierra

Posted on October 18, 2025October 18, 2025 by Hannes Baumann

Expanding the Silverside System | Blog

15 October 2025. While the embryos from Iquique and Dichato develop and now begin to hatch in the warmest temperatures, Hannes and Claudio took a quick trip to get embryos from a third population at ~ 30S. It's where the Chilean coast is as wild and rugged as anywhere else, but the trees have already given way to prickly shrubs and lots and lots of cacti - the desert begins. It's also the area around the big double city of Coquimbo/La Serena, where already in 2023 we ran into trouble finding pejerrey, let alone spawning ripe ones. Back then, we thought of it as an aberration, something surely owed to the strong El Niño phenomenon of 2023 - but nothing permanent.

IQ23hatch — Newly hatched Chilean silversides (*Odontesthes regia*) from the Iquique population

And so here we are again. And to our chagrin, again the fishermen in the Coquimbo fish market just shrug and point to the pejerrey they sell. No, those are not local at all; they are from the south of Chile in Puerto Montt.

So again we follow our instincts back to the small cove, where we had some (some!) luck the last time around - Caleta Sierra. Again we meet up with Mauricio Vega, the fisherman who wants to help us. And again we try at night and in the morning to row a gill net around a stretch of the small pebble beach of the cove and then pulling it ashore. We do catch all kinds of fish that way, just not the ones we are after! In total, the whole effort netted no more than five pejerrey, all but one unripe.

We return empty handed, pondering the truism that nature just doesn't care about science projects. To me, it seems timely to rethink whether this species truly has a continuous or perhaps discontinuous distribution along the Chilean/Peruvian coast.

Chilean silversides are spawning in Iquique and Dichato

Posted on October 8, 2025October 20, 2025 by Hannes Baumann

7 October 2025. Its been a truly wild last few days. In Dichato, we were racing against time to get all the setup ready, including an emergency bus trip overnight to Santiago to retrieve the missing chillers from a central aquarium store, and a Saturday morning frenzied work session to get everything up and running before the first sampling trip to the north. On Saturday night Hannes flew to the desert city of Iquique at 20S, a place of unreal beauty and harsh landscapes of sand, rocks, and ocean.

Thanks to the incredible help and expertise from local collaborators Prof. Miguel Araya and Dr. Cristian Asocars, the Sunday (5 Oct) morning fishing via gill net was almost too good to be true. With just one cast, we caught upwards of 400 Chilean silversides, all running ripe - perhaps inspired as we often found for northern hemisphere silversides - by the full moon. The fertilization in the boat and then transport of the embryos back to the lab via airplane all went without problems - a rare moment to cherish as an experimenter.

The kicker? The same full moon also appeared to entice the silversides in Dichato, and so a spontaneous fisherman went out with Hannes Tuesday night to - lo and behold - again catch all the fish, all running ripe, we needed to start the second population of the experiment.

48 hours. 2 populations more than thousand miles apart sampled and brought as embryos into the common garden experiment. Maybe I should consider a generous offering to San Pedro, the saint of the fishermen whose statue is in everything fishing harbor in Chile.

Hannes back in Chile to repeat common garden experiment!

Posted on September 28, 2025September 28, 2025 by Hannes Baumann

25. September 2025. I have been asked by quite a few people (on both hemispheres), why I had to go again to Chile, to the same place, the same marine station, to repeat the same experiment from two years ago? Did the first fail somehow? No, not at all. The first experiment yielded really intriguing data suggesting similar local adaptation patterns in southern compared to northern hemisphere silversides.

But the catch is that one year could be a coincidence. To make statistically robust inferences about the nature of local adaptation in Chilean silversides, good science simply demands another, a second independent data set of observations. Even more so, because (i) the adaptation strength here is likely subtle, and (ii) some treatments and populations were indeed less successful the first time around.

And so I'm here again. The place where I spent 6 months during my sabbatical feels wonderfully familiar - despite being thousands of miles away from home. The setting September sun pours gold over the halfmoon-shaped Coliumo Bay. Spring is in the air here, but the little beach town is still mostly void of the summer crowds. I wander through the streets, recognize the stray dogs, and many of the people in this little village say they remember me and my family from two years ago.

In the marine station, the experiment is now being set up in a different location. Inside the aquarium, which is climate-controlled and therefore more suitable. It took us two years to gain permission to move in, and I had to have custom tanks made to set it all up. Will it all be worth it?

Now time is really tight, the setup needs to be put together in just a few days, because in the low latitudes of Chile's north, the spawning season of pejerrey has already begun. Fingers crossed.

Hannes starts sabbatical research in Chile

Posted on July 22, 2023August 12, 2023 by Hannes Baumann