Figure 1: Rainbow Trout (photo courtesy of the U.S Fish and Wildlife Service)
Rainbow Trout are one of the many fish species that are affected by harmful algal blooms (HABs). Harmful algal blooms occur all over the world, in freshwater and seawater, which makes them a very troubling issue. Not only do they cause damage to fish and aquatic ecosystems, but they can also negatively impact many other factors such as tourism, public health, and recreation (Gobler, 2020). Humans play a significant role in causing HABs, whether its adding extra nutrients (for example, phosphorous or nitrogen) into the water or contributing to climate change (Sellner et al., 2003). Two examples of humans adding extra nutrients into the water are agricultural runoff and industrial activity. The extra nutrients that these activities provide promotes higher rates of algae growth than usual (Sellner et al., 2003). Further, humans have contributed significantly to climate change, which raises water temperature, providing an excellent habitat for algae to live in and take over (Ho and Michalak, 2019). HABs also occur in Lake Erie, mostly in the Ohio Maumee watershed because of the agricultural practices that are dominant within that watershed.
In aquatic ecosystems, HABs cause hypoxia, which is condition where there are extremely low levels of oxygen in the water (Golber, 2020). Fish, such as the rainbow trout, do not breath air, but they still need oxygen in order to survive. The fish’s gills are huge compared to the fish’s body, which provides a lot of help when absorbing oxygen (Ness Foundation, 2019). In addition, when a fish breathes, the water flowing over the gills runs the opposite direction of the blood running through the gills, which allows the amount of oxygen in the blood to be less than the oxygen of the water (Ness Foundation, 2019). This allows oxygen to move to places where there are low amounts of oxygen, which refers to a process called diffusion. Once in the fish’s body, the oxygen attaches to a protein called hemoglobin, and it is transferred all throughout the body (Ness Foundation, 2019). Algae effect the fish’s ability to breathe by irritating the gills, which decreased the amount of oxygen that the fish receives (Svendsen et al., 2o18). If there is more algae in the water, then fish have a higher chance of suffering from this condition.
Figure 2: Oxygen transferred to blood via the veins as water flows through
(Photo courtesy of Charles Molar and Jane Gair, CC BY 4.0 DEED https://creativecommons.org/licenses/by/4.0/)
In order to prevent further damage caused by HABs, there has to be a reduction in agricultural runoff entering the water body. There is action being taken to minimize impacts caused by agricultural runoff, such as a reducing pesticide use, managing irrigation systems, and conservation tilling (Marsh, 2022). Industrial activity needs to be reduced or better managed to prevent nutrient-rich runoff that comes from industrial plants. The whole problem of climate change is an extremely complex problem, and there are many measures that humans can take to reduce their impact. For example, carpooling or taking the bus instead of driving most times can limit emissions from cars, which contributes to climate change. Fish are a huge part of the aquatic ecosystem, and humans need to do their part to reduce excess nutrient input into water bodies in order to protect fish.
Sources:
Gobler, C. J. (2020). Climate change and harmful algal blooms: Insights and perspective. Harmful Algae, 91, 101731. https://doi.org/10.1016/j.hal.2019.101731
Ho, J. C., & Michalak, A. M. (2019). Exploring temperature and precipitation impacts on harmful algal blooms across continental U.S. lakes. Limnology and Oceanography, 65(5), 992–1009. https://doi.org/10.1002/lno.11365
How do fish breathe? The Science Behind Gills. New England Science & Sailing (NESS). (2019, August 8). https://nessf.org/how-do-fish-breathe-the-science-behind-gills/
Marsh, J. (2022). Protecting water quality from agricultural runoff. Agrilinks. https://agrilinks.org/post/protecting-water-quality-agricultural-runoff
Sellner, K. G., Doucette, G. J., & Kirkpatrick, G. J. (2003). Harmful algal blooms: Causes, impacts and detection. Journal of Industrial Microbiology and Biotechnology, 30(7), 383–406. https://doi.org/10.1007/s10295-003-0074-9
Svendsen, M., Andersen, N., Hansen, P., & Steffensen, J. (2018). Effects of harmful algal blooms on fish: Insights from Prymnesium Parvum. Fishes, 3(1), 11. https://doi.org/10.3390/fishes3010011