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Induced Sex Change in US Fisheries: Drop in the Bucket or Nail in the Coffin?

     Recently in class, we've been examining sex determination and reproductive development. One topic in particular that stuck out to me was the idea of sex change at the adult stage of an organism's life. Such an incredible display of plasticity is very fascinating to me, and I've been thinking about the literature we've taken a look at in class (Matsumoto et al. 2014 & Capel et al. 2017). On one hand, we've seen how exposure to PCB's at the embryonic stage in turtles can redirect gonadal directory (Matsumoto et al. 2014), and on the other hand we learned how adult fish can change sex based on visual and social cues (Capel et al. 2017). Something significant that I feel like we haven't covered but I'm familiar with from past courses is the effect of pollution (PCB's and estrogen in particular) on the endocrine system in fish species. 

    Wastewater treatment runoff into streams wreaks havoc on aquatic species. Chemicals acting as endocrine disruptors alter reproductive characteristics of local species, including creating intersex conditions for fish among a plethora of other sub-lethal effects. Wastewater runoff isn't uncommon in the US; in regions of the Southeast, 70-90% of fish sampled in the Southeast are intersex. Other factors besides wastewater runoff such as runoff from enclosed livestock operations can contribute to increased levels of endocrine disruptors in riverine systems, but sometimes drivers of increased endocrine disruptor levels are not so clear. In a study done by Kellock et al. in 2014, 48% of largemouth bass found in impoundment sites in Georgia were intersex and on average were shorter and smaller than their conspecifics. In this case, a striking proportion of the sampled population was intersex in spite of considerable isolation from human inputs (WWTP's or septic tanks). This is extremely alarming because we don't even know the source of contamination. 

    To add on to the effects of climate change and other issues, this problem also has large implications on fisheries across the country. Affected individuals suffer from decreased fecundity and viability in the face of induced intersex conditions. This further contributes to the decline we see now in fisheries around the world. On the bright side, I think this is an issue that could see improvement because of public interaction with fish of recreational value (i.e., largemouth bass). Once people begin to directly experience the effects of these induced changes to recreational fish populations, it will be easier to gather support for funding more research and developing strategies to mitigate the effects of what we see happening now. What's yet to be seen are the longstanding effects of this issue. How will generations look further down the line? What do wild populations truly look like now? What solutions can we come up with to reduce disruptive inputs? 



Sources:

Matsumoto Y. et al., 2014. Embryonic PCB exposure alters phenotypic, genetic, and epigenetic profiles in turtle sex determination, a biomarker of environmental contamination. Endocrinology 1-11. 

Capel B., 2017. Vertebrate sex determination: evolutionary plasticity of a fundamental switch. Genetics 1-15. 

Kellock K.A. et al., 2014. Survey of Intersex Largemouth Bass from Impoundments in Georgia USA. Transactions of the American Fisheries Society 143:565–572. 

https://youtu.be/a1MsWUGkOFE

Comments

  1. Kiersten NelsonMarch 15, 2021 at 8:26 AM

    Wow, this is really interesting. I had no idea that some regions in the southeast 70-90% of fish sampled were intersex. That is a crazy statistic. I would be interested in if these trends we see in the US are the same across other large developed countries or if the US is an exception.

    ReplyDelete
  2. Jared BennettMarch 30, 2021 at 8:33 AM

    This is super interesting! Most of my work is with SE fishes and so I am curious as to how I could assess this in the field. Something I have noticed over the last few years is that it is extremely difficult to sex fish in the field (particularly bass and other fish in non-breeding seasons). I think training of fish biologists to be able to collect some measure of data on this while sampling could lead to a really interesting data set, especially when paired with the water parameters that are usually taken while sampling. Cool blog! -Jared

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