Researcher spotlight

Life history of live-bearing fish in Rio de Janeiro

Hi everyone, it’s me

Welcome to Cardio & Conservation - Researcher Spotlight! In these posts I ask fellow students, academics, and industry professionals to make their science accessible. I want you to hear of the amazing work scientists are doing, in easy to understand terms - with the hope that this will help to increase interest and understanding of often complex studies.

Our first Spotlight comes from Oliwia Konecka - a lab-mate at RHUL who is embarking on her Master’s Research project on live-bearing fish.

Over to Oliwia!

Hello! My name is Oliwia and I am starting my masters journey this year (WOO)!

So, a little introduction to me. Earlier this year I graduated from Royal Holloway with a first-class Zoology degree. After 3 years of incredibly hard work and dedication, I was incredibly proud of myself and of so many of my friends.

My final year was definitely something.

I did my final year project on how light pollution affects the distribution of small mammals, finding that, unsurprisingly, small mammal populations tend to decrease with light pollution, however this effect was much more prominent with streetlights (rather than motorway lights), and with females rather than males.

I could write so much more but that research is not what this post is about.

I have a major interest in evolutionary ecology and how an animal's environment can impact them over time. With our current changing world, where never before seen temperatures are being reached, and habitats are being altered like never before, the importance of this research field is growing.

I am now starting my Masters in Biological Sciences by Research, looking at how differences in salinity and competition impact the life-history characteristics of two species of live-bearing fish, the Southern Molly (Poecilia vivipara) and the January Toothcarp (Phalloptychus januarius), in coastal Rio de Janeiro.

Rio de Janeiro, Brazil. Oliwia’s research will focus on two species of fish found in coastal Brazil. [Unsplash]

Okay, now what does that actually mean? Well, these fish live in waters that vary extremely in how salty they can be, and in some cases, these fish inhabit these waters together and in some alone. So, my goal is to see how some of the characteristics and traits they develop or show throughout their life differ in these different habitats. This will give us an idea as to how certain factors may affect certain organisms.

This will involve going to different lagoons in Brazil where these fish are present and testing the salinity (and other factors) of the water and whether one species is present alone or with the other. Then, net sampling a few males and females, to take back to the lab, where I measure, weigh, and dissect them. Dissection and desiccation of their reproductive organs and any offspring (because “live-bearing” fish produce live young rather than laying eggs) will tell me how much of their resources they will delegate to reproduction compared to their own survival.

For example, will fish in more saline environments prefer quantity or quality of offspring? Will they have a higher fat content? Higher relative mass? Similar questions can be asked regarding competition. Hopefully, I will find some answers, and maybe I can relay them back to you at some point.

This research is important because the results may allow us to predict how animals may respond to a change in their environment. In this case, how live-bearing fish respond to salinity and competition differences.

Freshwater habitats are quite vulnerable, as human and natural activity is resulting in salinisation of many freshwater bodies. Understanding how competition affects animals is also vital, due the global threat of invasive species (e.g. freshwater guppies in much of South and Central America) and how habitats are changing. Animals may be pushed to locations not previously seen before, dealing with new competitors and predators, and therefore being forced to adapt, or suffer the consequences.

Wish me luck on my journey!

I hope you enjoyed hearing about Oliwia’s project - Oliwia will be heading over to Brazil next month (November 2025) to undertake her field research. I’m hoping to catch up with Oliwia, and all of the other student researchers who we spotlight on the blog, to see the outcomes of their research. And, I will shortly be posting an author Q&A, watch out for that below.

In the meantime, if you have any questions for me or Oliwia, any suggestions, feedback or interesting topics for the blog, please get in touch.

Until next time!