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#           Exposure to Estrogenic Endocrine-Disrupting Compounds Can Lessen the Reproductive Condition of Adult Male Largemouth Bass (Micropterus salmoides)      

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      By Columbia Environmental Research Center      October 2, 2023    

            -              Overview           

Summary of the published study: Declines in Reproductive Condition of Male Largemouth Bass (*Micropterus salmoides*) Following Seasonal Exposure to Estrogenic Endocrine-Disrupting Compounds

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Fish kill events, disease outbreaks, skin lesions, and abnormalities in reproductive organs have been seen in wild populations of bass species throughout the United States. The timing of these events suggests influence from human activities. For example, heavy rains can cause increased runoff of pesticides and hormones from agricultural lands. The increased runoff and agricultural land use have been associated with poorer fish health.

This leads us to ask questions about how chemicals and hormones in the environment, stemming from human activity, possibly impact fish reproduction and subsequently the overall health of fish populations. Reproductive abnormalities in particular could lead to possible effects at the population level, have been observed in wild fish throughout the United States, with high prevalence in largemouth bass (LMB; *Micropterus salmoides*) and smallmouth bass (*Micropterus dolomieu*).

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To investigate these connections with a few well known and prevalent contaminants, we tested if hormone and/or pesticide exposure during the early part of the fish reproductive cycle impacted the male fish’s later reproductive condition and readiness to spawn.

Estrone (E1) and atrazine (ATR) are common environmental contaminants often associated with agricultural land use. 17alpha-ethinylestradiol (EE2) is a contaminant associated with wastewater treatment effluent, and a representative, well-studied estrogen commonly used for fish toxicity testing.

To accomplish this, we tested how adult LMB responded to controlled pond exposure (Figure 1) of either EE2 or a mixture of E1 and ATR, compared to control fish. They were exposed during the early stage of the gonad regeneration and preparation for the coming spawning season (gonad recrudescence), which was hypothesized to be a time of particular sensitivity to effects from contaminant exposure. The responses measured in this study included gonadosomatic index (GSI; an indicator of the fish’s readiness to reproduce), as well as sperm cell count and mobility (indicators of the fish’s fertility).

The average concentrations of chemicals in the outdoor experimental ponds were monitored weekly throughout the exposure. Mean water concentrations in the treatment ponds were E1 (47.9 ng/L), ATR (5.4 μg/L), and EE2 (2.4 ng/L) (Figure 2 A–C). Dosing was stopped in December, and within a month the average concentration of EE2 was 0.1 ng/L and E1 was 2.9 ng/L. However, ATR continued to persist at an average of 2.9 μg/L throughout the remainder of the study (May). Water quality parameters varied seasonally, but there were no significant differences among the different experimental ponds.  

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Table S1

GSI was significantly reduced in E1 + ATR (*p* < 0.05) and EE2 (*p* < 0.003) exposed males compared to control at every time point after early gonad recrudescence (December, April, and May; Figure 2 D).

Sperm motility (percent total and progressive motility per sample) assessed at the April sampling timepoint was significantly reduced in both the E1 + ATR (*p* < 0.006) and EE2 (*p* < 0.02) treatments compared to control (Figure 2 E). A decline in sperm count was also observed in the E1 + ATR (*p* < 0.03) treatment compared to control (Figure 2 F).

Taken together, our data indicate that environmentally observed concentrations of E1 + ATR or EE2 only can contribute to reduced reproductive condition and function in adult male LMB. Reduced GSI, sperm motility, and sperm counts have implications for the reproductive readiness and fertility of these male LMB. Early recrudescence appears to be a sensitive window in the adult male LMB reproductive cycle, and effects of exposure during recrudescence persisted throughout the following spawning cycle. The mechanisms of action and potential population-level consequences of reproductive effects of exposures to these environmental endocrine disruptors still require further investigation.  

 

 

 

 

 

 

Summary of the published study: Declines in Reproductive Condition of Male Largemouth Bass (*Micropterus salmoides*) Following Seasonal Exposure to Estrogenic Endocrine-Disrupting Compounds

Read the paper

 

Fish kill events, disease outbreaks, skin lesions, and abnormalities in reproductive organs have been seen in wild populations of bass species throughout the United States. The timing of these events suggests influence from human activities. For example, heavy rains can cause increased runoff of pesticides and hormones from agricultural lands. The increased runoff and agricultural land use have been associated with poorer fish health.

This leads us to ask questions about how chemicals and hormones in the environment, stemming from human activity, possibly impact fish reproduction and subsequently the overall health of fish populations. Reproductive abnormalities in particular could lead to possible effects at the population level, have been observed in wild fish throughout the United States, with high prevalence in largemouth bass (LMB; *Micropterus salmoides*) and smallmouth bass (*Micropterus dolomieu*).

View Media Details

To investigate these connections with a few well known and prevalent contaminants, we tested if hormone and/or pesticide exposure during the early part of the fish reproductive cycle impacted the male fish’s later reproductive condition and readiness to spawn.

Estrone (E1) and atrazine (ATR) are common environmental contaminants often associated with agricultural land use. 17alpha-ethinylestradiol (EE2) is a contaminant associated with wastewater treatment effluent, and a representative, well-studied estrogen commonly used for fish toxicity testing.

To accomplish this, we tested how adult LMB responded to controlled pond exposure (Figure 1) of either EE2 or a mixture of E1 and ATR, compared to control fish. They were exposed during the early stage of the gonad regeneration and preparation for the coming spawning season (gonad recrudescence), which was hypothesized to be a time of particular sensitivity to effects from contaminant exposure. The responses measured in this study included gonadosomatic index (GSI; an indicator of the fish’s readiness to reproduce), as well as sperm cell count and mobility (indicators of the fish’s fertility).

The average concentrations of chemicals in the outdoor experimental ponds were monitored weekly throughout the exposure. Mean water concentrations in the treatment ponds were E1 (47.9 ng/L), ATR (5.4 μg/L), and EE2 (2.4 ng/L) (Figure 2 A–C). Dosing was stopped in December, and within a month the average concentration of EE2 was 0.1 ng/L and E1 was 2.9 ng/L. However, ATR continued to persist at an average of 2.9 μg/L throughout the remainder of the study (May). Water quality parameters varied seasonally, but there were no significant differences among the different experimental ponds.  

View Media Details

Table S1

GSI was significantly reduced in E1 + ATR (*p* < 0.05) and EE2 (*p* < 0.003) exposed males compared to control at every time point after early gonad recrudescence (December, April, and May; Figure 2 D).

Sperm motility (percent total and progressive motility per sample) assessed at the April sampling timepoint was significantly reduced in both the E1 + ATR (*p* < 0.006) and EE2 (*p* < 0.02) treatments compared to control (Figure 2 E). A decline in sperm count was also observed in the E1 + ATR (*p* < 0.03) treatment compared to control (Figure 2 F).

Taken together, our data indicate that environmentally observed concentrations of E1 + ATR or EE2 only can contribute to reduced reproductive condition and function in adult male LMB. Reduced GSI, sperm motility, and sperm counts have implications for the reproductive readiness and fertility of these male LMB. Early recrudescence appears to be a sensitive window in the adult male LMB reproductive cycle, and effects of exposure during recrudescence persisted throughout the following spawning cycle. The mechanisms of action and potential population-level consequences of reproductive effects of exposures to these environmental endocrine disruptors still require further investigation.