Have you ever wondered what fish do all day? FISHBIO scientists are always curious about what fish are up to in the rivers we study, so last summer we geared up in our snorkel equipment and set up a few underwater cameras to find out! We were interested in seeing how the temperature of the river water affects the swimming and feeding activity of rainbow trout. Once we found groups of trout in the river, we set up underwater video cameras close by, and left them to film the fish for half a day. It was very important that we recorded the fish without disturbing them so we could document how fish behave normally in their river habitat.
We then took these videos back to the lab, where we watched the footage to measure the swimming and feeding activity of the fish. When fish swim faster, they beat their tails faster, so we measured swimming activity by counting how many times the fish beat their tails every 10 seconds. To measure feeding activity, we counted how many times the trout lunged for food particles every minute. These measurements tell us a lot about how well fish are doing when their river water gets warm. Tail beat measurements of fish in the river can be paired with laboratory swimming measurements, like our swim tunnel respirometry study, to predict how much energy the fish are using just to keep their bodies functioning in the river, and how much energy they have leftover to perform other activities, like eating or escaping predators, that are necessary for survival.
As the water gets warmer, fish use more energy just to survive. They also need to eat more food to support this higher energy expenditure, so their feeding activity increases – which also requires a lot of energy. Higher energy requirements mean the fish needs to eat even more food. But when the water temperature gets too high, fish do not have enough energy left over to capture and digest their food, so feeding activity decreases. If the fish cannot escape to cooler water, they will not grow, or may even starve to death. We’ll keep you posted on what we find out from this video footage. We may have the makings of a trout reality show on our hands!