Why Your Chicken Eggs Smell Fishy – and What to Do

While I love eating fresh eggs, sometimes you get an egg that just smells fishy. And then it tastes weird and fishy, too. So why do some chicken eggs smell fishy? And what can we do to prevent them?

Chickens eggs smell fishy due to nutrigenetics (a combination of nutrition and genetics). The most common nutritional cause of fishy eggs is too much canola meal, while brown-shelled egg-laying hens are genetically more likely to lay fishy-smelling eggs if fed elevated levels of canola meal.

Even so, there are several things you can do to prevent the fishy egg smell – so that you can enjoy your backyard flock and have fish-smell-free eggs of all colors. Keep reading to find out exactly what to do, based on my extensive research!

Why Do My Chicken Eggs Smell Fishy?

Researching this topic has been very enlightening for me personally. It’s helped me realize that the reason I didn’t like eggs growing up is that we bought cheap eggs – many of which were fishy tasting. No wonder I hated eggs as a kid!

Now that I have access to the backyard homestead, fresh eggs our chickens lay, they aren’t fishy smelling or tasting. They’re delicious! But let me share with you what I discovered in my research.

The fishy, decaying smell is caused by trimethylamine (or TMA). TMA is a common byproduct of normal digestion processes. Specifically, it’s caused by the fermentation of choline in a chicken’s gut. Then, the next step of digestion is when the very stinky TMA is processed into the safe and odor-free trimethylamine N-oxide (TMAO). That way, everyone is happy with the regular-smelling egg product.

However, this normal process doesn’t work as well in two specific cases.

1. There’s an elevated level of TMA in the chicken’s digestive system due to its dietary intake. With too much TMA, the chicken’s gut can’t process it all into TMAO. The excess TMA accumulates in the yolk and results in a fishy-smelling egg.
2. The chicken has a recessive genetic mutation that makes it harder for it to process TMA into TMAO. These chickens are more likely to experience the above process even if fed smaller quantities of food that lead to TMA. Brown-shelled egg-laying chickens are more likely to have this specific genetic mutation.

In other words, the most common cause of fishy smelling chicken eggs is their diet. And, of the foods that lead to fishy eggs, my research shows that canola meal (rapeseed meal) is the most common culprit.

My research also shows that brown-shelled egg-laying hens have an increased likelihood of laying fishy eggs – due to the potential for a genetic mutation that affects their ability to process TMA. This doesn’t mean you should avoid brown-shelled egg-laying hens, though. Rather, it just means you need to know that they may be more likely to lay foul-smelling eggs if you’re feeding them lots of canola meal.

Does that mean all canola meal should be avoided, especially for the brown egg-layers? No. But we’ll talk about that later on in this article.

What Causes Chicken Eggs to Smell Fishy

Based on my research, the most common cause of fishy-smelling chicken eggs is too much canola (or rapeseed) meal in the chicken’s diet. However, it usually has to be a pretty significant percentage of the chicken’s feed to cause problems – unless the chickens have the genetic mutation that makes it harder for the chicken to process the TMA into TMAO.

Poultry scientists and nutritionists are aware of the genetic mutation. The mutation is more common in chickens with brown eggs. And since there is an increased prevalence of brown-shelled egg-laying chickens here in the United States, that’s something that poultry scientists and nutritionists have to account for when making chicken feed.

How Much Canola Meal Can Chickens Have Before Eggs Get Fishy?

Based on my research, the problematic percentage of canola meal leading to fishy-smelling eggs is as low as 3% of a chicken’s feed – for susceptible hens. Increasing the percentage of canola meal to 10% was associated with the chickens developing goiters, which led to thyroid-related and other health issues. Some chickens didn’t produce fishy eggs until the canola meal reached 15-20% of their intake. In other words, chickens can’t consume large quantities of canola or rapeseed meal without it becoming problematic quickly (Ward, 2008).

So in any case, general poultry feed is generally balanced according to these parameters – to prevent both fishy-smelling eggs and long-term health issues in our chickens.

However, canola doesn’t have to be avoided completely. In fact, some canola meal in the chicken’s diet is usually okay. It’s a great way to add some extra omega-3’s to your chicken’s diet to improve their health and the health of eggs for our benefit.

It’s when the levels of canola meal (usually abbreviated as CM in the research literature) get to those higher levels mentioned that it becomes problematic for egg taste.

How to Prevent Fishy Smelling Chicken Eggs

The first thing to do to prevent fishy-smelling eggs is to be aware of what you’re feeding your chickens.

So, I did some research into the most common chicken feeds that we, as backyard homesteaders can buy. It turns out that for most chicken feed, canola is usually just a minor additive for extra omega-3’s – and it’s not in any amount that should risk fishy-egg smells.

Most chicken feed is a combination of:

• Cereal grains – like corn, wheat, barley, rye, oats, and sorghum.
• Protein meals – from vegetable and/or animal sources, such as oilseed meals, fish byproducts, and legumes.
• Fats and oils – from various oil sources including soy, sunflower, linseed, palm, and cottonseed. Depending on your location, canola may also be used.
• Minerals and vitamins – a variety of micronutrients to make sure your chickens are getting what they need.
• Feed additives – this may include crushed oyster shells, probiotics, omega-3’s, or other additives depending on the type of feed.
• Miscellaneous raw materials (such as roots and tubers) – this will also depend on the feed brand and type.

So as you are buying chicken feed, just read the list of ingredients. Make sure that any canola based products (also known as rapeseed) are additives rather than main ingredients – and you should be okay. When in doubt, feel free to ask a knowledgeable employee, farmer, or backyard homesteaders if the brand in question is safe for brown-shelled egg layers.

Then, test the feed with your chickens for five days. Fishy eggs usually appear within five days of a canola meal being incorporated into a diet (Ward, 2008).

• If your chickens don’t lay any fishy eggs in that timeframe, you’re on your way to preventing fishy eggs.
• If your chickens do lay tainted eggs, simply remove the canola meal from their diet. A change in diet should immediately fix the fishy-smelling egg problem.

Then, just be aware of what treats you’re giving your chickens. Keep any treats with canola in them to a minimum. And feel free to test how it affects your chickens. Or just switch to a different kind of seed-based treat altogether. Sunflower seeds are a great alternative that shouldn’t affect egg flavor.

The last thing to do in order to prevent fishy-smelling eggs is to be aware that brown-shelled egg-laying chickens are more likely to lay tainted eggs. However, if you control your chicken’s feed intake by offering canola meal-limited feed, this option doesn’t have to be a major determining factor.

After all, many brown-eggshell laying chickens are amazing layers. It would be a shame to skip having them in your flock – especially if you’re already keeping your other chickens on a fishy-egg free feed plan.

Are Fishy Smelling Chicken Eggs Safe to Eat?

Based on my research, fishy-smelling eggs are generally safe to eat.

However, in my own experience as a child eating fishy-smelling eggs, they do have an off-flavor and taste that’s unpleasant. Others report not minding the smell and taste – provided they flavor the eggs well enough.

So if your hens lay fishy-smelling eggs, it’s up to you if you’d like to eat the eggs or not.

Going forward, just remember to evaluate your chicken feed and adjust it if need be. Then, give your chickens a few days to flush all that TMA out of their systems so you can enjoy fishy-smell-free eggs again.

Resources

Learning from your own experience is essential, but learning from others is also intelligent. These are the sources used in this article and our research to be more informed as homesteaders.

1. Hawrysh, Zenia J., et al. “Influence of Rapeseed Meal on the Odor and Flavor of Eggs from Different Breeds of Chickens.” Canadian Institute of Food Science and Technology Journal, Elsevier, 18 Apr. 2013, www.sciencedirect.com/science/article/abs/pii/S0315546375737021.
2. J. Agric. Food Chem. 1982, 30, 1, 9-14Publication Date:January 1, 1982 https://doi.org/10.1021/jf00109a002
3. March, B. E., and Carol MacMillan. “Trimethylamine Production in the Caeca and Small Intestine as a Cause of Fishy Taints in Eggs.” Sciencedirectassets.com, University of British Columbia Department of Poultry Science, 1978, https://www.sciencedirect.com/science/article/pii/S0032579119553214.
4. “US5012761A – Chicken Egg Having Relatively High Percentage of Long-Chain Fatty Acids and Method of Reducing Heart Related Disease in Humans Using Such Eggs.” Google Patents, Google, patents.google.com/patent/US5012761A/en.
5. Vondell, JH. “Detection of Chickens Laying ‘Fishy Eggs.’” ScienceDirect.com, Poultry Science, 1948, https://www.sciencedirect.com/science/article/pii/S0032579119506150.
6. Ward, A.K., et al. “Fishy-Egg Tainting Is Recessively Inherited When Brown-Shelled Layers Are Fed Canola Meal.” Poultry Science, Elsevier, 11 Dec. 2019, www.sciencedirect.com/science/article/pii/S0032579119391400.
7. Ward, Alison. (2008). Genetic and dietary interactions of fishy-egg taint in brown-shelled laying hens. University of Saskatchewan Department of Animal and Poultry Science, www.researchgate.net/profile/Alison_Ward2/publication/216346809_Genetic_and_dietary_interactions_of_fishy-egg_taint_in_brown-shelled_laying_hens/links/00b49528b7a1772d4d000000/Genetic-and-dietary-interactions-of-fishy-egg-taint-in-brown-shelled-laying-hens.pdf.