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Biochemistry

Ch-Ch-Ch-Changes in Seahorse Hormones

While we already know that plastics are harmful to the environment, do you ever really think about how they can cause negative impacts? Not just by their physical presence like microplastics, but when the plastics start to breakdown and chemicals get released into the environment. Would you believe that the single-use plastic water bottle that you drank from had a chemical within that, if it leaked into the water, could have changed the hormone levels in your body?

Two white lab mice. One is small and one is large. The large one is impacted by endocrine disruption.

Two mice demonstrating a possible effect of endocrine disruption. These hormones in turn impact the body functions and chemical processes of an organism. The smaller mouse on the left has normal endocrine function; meanwhile, the mouse on the right side is exhibiting obesity due to endocrine disruption. Picture Credit: Modified from File:Endocrine disrupting chemicals – ABC’s of EDC’s – results from a regional science forum for the Mid-Atlantic (November 2006) (IA CAT30984096).pdf – Wikimedia Commons.

BPA & BPA-Free

Bisphenol A (BPA) is a chemical compound that is commonly found in consumer goods like plastics, and it is a harmful endocrine disruptor, which means that it can harm an organism’s reproductive, immune, and neurological systems. Simply put, this chemical can change the hormone levels and responses in an animal when too much of it is present. Products you may use like plastics and canned goods tend to contain BPA and while BPA doesn’t seem to be a problem in low doses, this chemical compound can accumulate in the environment and lead to some major health problems for both humans and animals.

People have started to remove BPA from products (labeled as BPA free) to reduce the impact this chemical can have on people who are concerned about its effects. However, this compound has already accumulated in aquatic environments and has been shown to impact the reproduction systems of various fishes.

Canned foods in a grocery store.

Canned foods can contain bisphenol A (BPA) in the lining of the can. Limiting the amount of canned goods that you eat can lower your BPA exposure. However, according to the FDA, low doses of this chemical have little to no impact on the regular function of a human’s body. Side effects are not seen until much higher concentrations accumulate in the body. Picture Credit: File:Import canned foods in Kobe.jpg – Wikimedia Commons.

Fish Eggs

Goldfish, fathead minnows, seabreams, and zebra fish are just a few examples of fishes that have shown the devastating effects of endocrine disruptors on their reproductive systems. Reduced egg size and abundance, reduced sperm counts, and increased “intersex” organisms (containing both the male and female reproductive organs) are issues arising from endocrine disruptor accumulation in the environment. The presence of “intersex” fishes has even been used as a bioindicator, a biological indicator for whether a water body has pollutants within the system that are impacting the animals living there, to demonstrate the decline in water quality of aquatic environments. The most common bioindicator is the decrease in egg size and abundance, which in turn effects the reproductive success of these fish (how many baby fish are born and live into adulthood to have their own offspring). What is unknown though, is how fish that reproduce unconventionally are impacted by endocrine disruptors like BPA.

Bowl of salmon roe. These are the little orange eggs.

A bowl of fish eggs (also called roe) are a food source for many animals, as well as people. However, the size and number of eggs present in a fish contributes to the fish’s reproductive success and any hormonal changes caused by chemical compounds in the environment can negatively impact the formation and development of these eggs. Picture Credit: File:Ikura – Salmon Roe.jpg – Wikimedia Commons.

The Unconventional Seahorse

Seahorses are different from most other fishes in that the males brood the eggs instead of the females. The female seahorses deposit the eggs into the male’s brood pouch and the males are the ones who take care of the eggs until they hatch.

A lined seahorse.

Like other seahorses, the lined seahorse male is the one who takes care of the eggs after the female deposits them in his brood pouch. This study looked at how BPA exposure impacted the female egg development, the male sperm development, and the maintenance abilities of the brood pouch to maintain the eggs during the development process. Picture Credit: File:Lined seahorse, Hippocampus erectus.jpg – Wikimedia Commons.

The scientists in this experiment wanted to know how reproduction for seahorses differs from other fishes (like those mentioned above) in response to increasing concentrations of BPA. The Lined Seahorse (Hippocampus erectus) was used for the experiments in this study. These seahorses were exposed to BPA concentrations proportional to concentrations that could be compared to those found in the environment – 10, 100, and 1000 micrograms per liter (think of it as low, medium, and high concentrations, respectively).

What they found was that the bioaccumulation of BPA increased with the increasing concentrations (more of the compound was incorporated into the tissues of the seahorse). The lower doses (10 and 100 micrograms per liter) had minimal to no side effects on the seahorse reproductive system. The high concentration of 1000 micrograms to liter, however, showed significant impacts on the reproductive systems of both the male and female seahorses. The females exhibited less egg production, the males had sexual hormone disruptions and brood pouch maintenance failure (tissue formation and repair disfunction). Thus, the BPA exposure at high concentrations negatively impacted the seahorses by impairing their egg development in a way similar to that in other fish species.

What’s the Big Deal?

This study demonstrates how important normal endocrine function is in animals in order for them to successfully live and reproduce. The introduction of the endocrine disrupting chemicals into the environment is concerning not only for the fishes mentioned here, but for people as well. After all, we are exposed to the environment too and eat the organisms within it that are accumulating these compounds. To assist with reducing and removing BPA from the environment, use BPA-free products and if you do happen to use any items that contain it, like canned goods, make sure they are recycled appropriately.

Reference:

Liu, Y., Wu, Y., Qin, G., Chen, Y., Wang, X., & Lin, Q. (2021). Bioaccumulation and reproductive toxicity of bisphenol A in male-pregnant seahorse (Hippocampus erectus) at environmentally relevant concentrations. Science of The Total Environment753, 141805.

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