Where does all that waste go?! The effect of estrogens and endocrine-disrupting compounds on fish reproduction

Have you ever wondered where things go after they’re flushed down the toilet? If you’re a kindred spirit, maybe you’ve written several term papers on waste water treatment. More likely, you’ve probably truly never given the process much thought or aren’t exactly dying to admit that you’ve spent time pondering the transport and fate of toilet waste. One of the most common misconceptions about biological waste is that it goes to a wastewater treatment plant and every single contaminant in the waste is filtered out. Unfortunately, this isn’t always the case. In humans, chemicals that contain estrogen (e.g., birth control) are metabolized in the body, however, a small amount of un-metabolized estrogens are excreted in urine or feces (Racz & Goel 2010). While it is true that wastewater treatment plants are able to remove almost one hundred percent of the estrogen in urine and feces, some cities still have combined sewers (i.e., underground pipes that store excess waste and precipitation until it is treated) in which it is possible for untreated wastewater to overflow into nearby waterways during periods of high precipitation. This means that untreated waste containing estrogen compounds enters streams directly (EPA 2017; Racz & Goel 2010). Unfortunately, these estrogens can have detrimental physiological impacts on fish reproduction. Additionally, naturally-occurring chemicals and man-made chemicals such as pesticides enter streams as runoff from agricultural fields and contain endocrine-disrupting compounds (EDCs) that mimic sex hormones, having similar negative physiological impacts on fish reproduction (Arcand-Hoy & Benson 1998).

Untreated wastewater being deposited into a stream from a combined sewer overflow (CSO) after a period of heavy precipitation (Image drawn by Krystal Pocock).

A fish being affected by the untreated wastewater from the combined sewer overflow (Image drawn by Krystal Pocock).


Endocrine-disrupting compounds can have detrimental effects on reproductive development during early life stages in fishes (e.g., larval, juvenile) (Arcand-Hoy & Benson 1998). Exposure to EDCs at the larval or juvenile stage can interfere with the determination (i.e., development) of sex organs and can even cause hermaphroditism, which occurs when an individual organism has both female and male sex organs (Arcand-Hoy & Benson 1998; Mill et al., 2011). While chemically-induced hermaphroditism does not always cause reproductive decline in fishes, there is evidence that hermaphroditism reduces the hatchability of eggs, the number of successful eggs, and swimming success (Hill Jr. and Janz 2003). Additionally, exposure to EDCs during the larval or juvenile stages can cause fishes to reach reproductive maturity earlier or later than expected, which can result in reduced lifetime reproductive output. Furthermore, male fishes exposed to estrogens or endocrine disrupting compounds later in life can experience feminization of the testes, which can negatively interfere with reproductive efforts. The processes by which these transformations occur in the body are complex, however, they have serious implications for fish reproduction (Arcand-Hoy & Benson 1998). In the future, proper management of wastewater and the phasing-out of CSO systems can help minimize the amount of estrogen-laden wastewater entering streams. Applying fertilizers and pesticides when there is little to no chance of precipitation will also help minimize the contamination of streams with endocrine-disrupting compounds.

Arcand-Hoy LD, Benson WH (1998) Fish reproduction: an ecologically relevant indicator of endocrine disruption. Environmental Toxicology and Chemistry 17(1):49-57.

Hill Jr. RL, Janz DM (2003) Developmental estrogenic exposure in zebrafish (Danio rerio): I. Effects on sex ratio and breeding success. Aquatic Toxcology 63(4):417-429.

Racz L, Goel K (2010) Fate and removal of estrogens in municipal wastewater. Journal of Environmental Monitoring 12:58-70.

EPA (2017) What are combined sewer overflows (CSOs)? Webpage. Retrieved from https://www3.epa.gov/region1/eco/uep/cso.html on 22 April 2019.

The physiological effects of angling stress on fishes

Bobbers in a pond (Image taken by Krystal Pocock)

Have you ever been catch-and-release fishing and found yourself wondering if the fishes you catch go on to live healthy, productive lives after you toss them back? Maybe you’ve contemplated how long it takes for the puncture mark left by your hook to heal or how removing fishes from the water for short periods of time affects them. If these thoughts have ever crossed your mind, you’re not alone. In fact, there has been a lot of research completed on the subject.  Studies have shown that catch-and-release fishing is one of the biggest sources of stress to game fishes (Meka & Mc Cormick 2004; Twardel et al., 2018). When a fish is exposed to extremely high amounts of stress, hormones that are produced by the stress response can be fatal. Luckily, complex processes in the body work to regulate hormone levels and are typically able to quickly return the body to its normal state before stress hormones are fatal. More often, angling-induced stress tends to have what is called sub-lethal effects, which cause other important functions in the body to slow down or stop altogether. As such, recovery from elevated stress levels in captured fishes requires a lot of energy and often causes energy to be taken away from other important functions like reproduction and survival to compensate (Meka & McCormick 2004).

Imagine you’re out fishing on a beautiful day and you’ve finally gotten a bite. What happens next can directly contribute to the amount of physiological stress that a fish experiences during catch-and-release angling. There are three major sources of stress and potential contributors to mortality that fish are exposed to while being captured: exhaustion from the reeling and landing process (i.e., the amount of time that it takes an angler to successfully remove the fish from the water), injuries from hooks, and air exposure (Meka & McCormick 2004). Just like humans, fishes can become extremely tired from too much exercise and the exercise fish get while an angler attempts to reel them in can be physically exhausting. If a fish has not fully recovered from reeling and landing exercise once they are returned to the water or quickly thereafter, they can easily be eaten by a larger fish (Meka & McCormick 2004; Twardek et al., 2018). Additionally, injuries obtained from hooks during the angling process can be deep and cause a lot of bleeding, which can cause death or infection (Meka & McCormick 2004). Furthermore, the longer that a fish is out of water and exposed to air, the more stressed they become (Meka & McCormick 2004; Ferguson & Tufts 1992). When fish cannot pass water over their gills to obtain oxygen, they start breathing very quickly, which causes a lot of carbon dioxide to accumulate in their bodies. Once there is excess carbon dioxide in their blood, fishes have a hard time retaining oxygen and can die if they aren’t able to obtain enough oxygen (Ferguson & Tufts 1992). Thus, exhaustion, injuries, and air exposure all have the potential to cause mortality, however, this is rare and typically happens under extreme circumstances.

More often, angling stressors such as those discussed above have sublethal impacts on fishes due to stress causing disruption of other important functions to compensate for the energy needed to recover (Meka & McCormick 2004). For example, sublethal impacts of stress associated with catch-and-release fishing are reduced reproductive output, reduced growth and time spent foraging, reduced immune response, and altered migration behaviors (Meka & McCormick 2004; Twardek et al., 2018). Additionally, research has shown that fish become more stressed as landing time, air exposure, and the time it takes to remove a hook increases. Fish are also more stressed when water temperatures are high (Meka & McCormick 2004). Furthermore, the longer fish are exposed to air, the longer it takes them to move again once they’ve been tossed back into the water (Twardek et al., 2018). One study even suggested that when fish are stressed, it can take as long as a day for stress levels to return to normal (Meka & McCormick 2004)!

Minimizing the time a fish is held outside of water, exposed to air, can greatly minimize the amount of capture stress (Meka & McCormick 2004; Photograph taken by Krystal Pocock).

Luckily, there are some best practices that anglers can utilize to reduce the amount of physiological stress that fish experience from catch-and release fishing. For example, using barbless hooks reduces injury during capture and use of natural bait can reduce injuries obtained from fish swallowing large, plastic lures (Brownscombe et al., 2017). Taking care to reduce the amount of time it takes to reel the fish in and time spent handling the fish out of water can also reduce stress. Finally, using specialized tools to remove hooks or cutting and leaving the hook in if it is found in a sensitive spot can reduce stress associated with angling (Brownscombe et al., 2017). Using smart angling practices can reduce stress and mortality associated with catch-and-release fishing and help ensure that there are future populations of fishes for years to come.

Brownscombe JW, Danylchuk AJ, Chapman JM, Gutowsky LFG, Cooke SJ (2017) Best practices for catch-and-release recreational fisheries- angling tools and tactics. Fisheries Research 186:693-705.

Ferguson RA, Tufts BL (1992) Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for “catch and release” fisheries. Canadian Journal of Fisheries and Aquatic Sciences 49:1157-1162.

Meka JM, McCormick SD (2005) Physiological response of wild rainbow trout to angling: impact of angling on duration, fish size, body condition, and temperature. Fisheries Research 72(2,3): 311-322.

Twardek WM, Gagne TO, Elmer LK, Cooke SJ, Beere MC, Danylchuk AJ (2018) Consequences of catch-and-release angling on the physiology, behavior, and survival of wild steelhead Oncorhynchusm mykiss in the Bulkley River, British Columbia. Fisheries Research 206:235-246.