Fish, glass, and tubing

It's June 2020, and while the weather is quite warm and sunny at Lammi Biological Station, I'm working indoors at the animal research facilities. The room I'm in is dimly lit; the temperature is something around 15°C, and thick window blinds cover the large windows that run along the south wall. We don’t want any light in here that we’re not in control of, and mostly we just want it fairly dark. The colors of this room are tank green, metallic wall white, opaque tube white, wire black, and wood board beige. 

The respirometry measurement setup

This is the experimental fish hall. For the past few months, my collaborators and I have been busy preparing an intricate system for doing a special kind of measurement on fish. Large tanks have been cleaned and modified, tubes measured and connected to all kinds of inlets and outlets, probes have been calibrated and a house-made electronic system has been set up to control it all. Submerged in the water-filled tanks are several small cylindrical glass chambers. In each chamber is a little fish; A juvenile Atlantic salmon. These glass chambers are more or less sealed so that nothing enters or leaves, though a few semi-transparent tubes, a miniature pump, and an oxygen probe make a closed circuit with the chamber, measuring the chambers oxygen content. Another set of tubes connects to a computer-controlled pump that replaces the water in the chamber every 20 minutes. The fish in these closed-loop chambers are slowly consuming the oxygen within them, and by measuring how quickly the oxygen decreases, we can calculate the fish’ rate of oxygen consumption. These chambers are called respirometers, and the procedure is called respirometry. The measured rate of oxygen consumption is used as a proxy for the fish' metabolic rate (their rate of energy consumption). Since we want to measure the metabolic rate when the fish is at rest (standard metabolic rate), the tank is covered with a thick tarp to keep the light out, and the fish stay in their chambers overnight.

One juvenile salmon inside one of our respirometers. (Photo: Sergey Morozov)

These measurements were a part of my doctoral research project, -and of our research group's larger overarching project. In this particular project, we're exploring the effects and mechanisms of vgll3, a gene that seems to have important effects on sexual maturation in Atlantic salmon.

 

Atlantic salmon, like all other animals, go through a process of sexual maturation as they age and develop. After having migrated out of their home river, these salmon spend some time at sea to grow large as they feast on the plenty of prey that they find there. Eventually, they return to their home river to reproduce. However, there is a lot of variation in the timing of maturation; Some individuals spend a short time at sea and return at a fairly small size, while others stay longer. What causes this variation? vgll3 has been shown to associate with some of this variation, and this gene comes in two different alleles (variants), E for early- and L for late maturation. We want to learn more about how this gene works; What are the mechanisms that make this gene do what it does?

 

This question was the reason these fish were put into these small glass chambers. Some of these juvenile salmon had the vgll3*EE genotype, while others had the vgll3*LL genotype; What we wanted to test was if there was a difference in these fish' metabolic rate. An earlier experiment had shown that fish with different vgll3 genotypes grow differently, and we wanted to see if this could be caused by a difference in metabolic rate. In a sense, we were asking if vgll3 might be something like an "energy allocation gene".

 

Months later, analyzing the data gathered from this project, we eventually found that there was no detectable link between vgll3 genotype and standard metabolic rate in the fish in our experiment*, indicating that the differences in maturation might not be connected to the resting metabolism and energy expenditure at the early life stage. Although this might sound like we found "nothing", it's still an important finding; Sometimes, ruling out a mechanism could be just as important as counting one in. Interestingly, in a similar, later experiment we did find some connection between vgll3 (plus another gene) and another metabolic trait, namely maximum metabolic rate**. You can read more about these findings by looking up the two research articles shown at the end of this post.

 

This project took a lot of effort to set up and run successfully, but it was also very fun and rewarding, and I'm incredibly grateful for my amazing collaborators and coauthors that turned this project into what it became. Being stuck inside a cold and dim hall isn’t so bad when you get to build cool projects, solve problems, and see it all work in the end. Whenever it may be, I'm looking forward to the next time.

 

A big thanks to Lammi Biological Station for housing our project at their premises, -especially for being so accommodating during the challenging COVID-19 pandemic. Also, thanks to the LBAYS foundation for their grant which supported this project.

 

Eirik Åsheim is a 2020 LBAYS grant recipient

 

*Åsheim, E. R., Prokkola, J. M., Morozov, S., Aykanat, T., & Primmer, C. R. (2021). Standard metabolic rate does not associate with age-at-maturity genotype in juvenile Atlantic salmon. Ecology and Evolution, 00, 1– 14. https://doi-org.libproxy.helsinki.fi/10.1002/ece3.8408

 

**J.M. Prokkola, E.R. Åsheim, S.M. Morozov, P. Bangura, J. Erkinaro, A. Ruokolainen, C.R. Primmer, T. Aykanat (2022, in production). Genetic coupling of life-history and aerobic performance in Atlantic salmon.

Proc. R. Soc. B.