Cats are carnivores, and as such, eating various kinds of proteins is good for their health.
Both cat food and cat treats contain all sorts of meat. Chicken is obviously the most common, but you can also find cat food containing turkey, lamb, and even deer. Insects are being seen as a valuable and eco-friendly future source of protein, so even insect-based cat food is starting to gain recognition and acclaim in recent years.
However, when you think of cats and food, the first thing to come to your mind is probably fish.
There's no denying cats love fish, and you may wonder what the harm is in letting them indulge every now and then. However, if your cat has kidney disease, then you should reconsider giving your beloved pet a fishy treat, especially in the case of tuna-based foods and snacks.
This is due to the mercury content in tuna. While the level of mercury in tuna and other fish does not pose a threat to healthy cats, it may prove critically dangerous to those with kidney disease due to their inability to expel waste from their bodies.
FDA Recommendations on Mercury Intake
The World Health Organization (WHO) and the U.S. Food and Drug Administration (FDA) have both issued the following advisories to reduce the intake of mercury resulting from the consumption of large fish:
- Pregnant and/or breastfeeding women and children should avoid consuming predatory fish that are higher up on the food chain.
- The above individuals should modify their weekly serving of fish, and choose from a wide range of fish lower in mercury, such as salmon, sardines, or tilapia.
Mercury Content in Commonly Consumed Fish and Meat
Then what’s the situation like for cats? A wide range of cat foods and snacks contain or are primarily based on fish. The mercury levels in the most commonly used fish are as follows.
- Predatory Fish (High on Food Chain):
- Swordfish: Average of 0.995 ppm, max of 3.22 ppm
- Shark: Average of 0.979 ppm, max of 4.54 ppm
- Tuna: Average of 0.689 ppm, max of 1.816 ppm - Predatory Fish (Medium on Food Chain):
- Sea Bass: Average of 0.219 ppm, max of 1.53 ppm
- Halibut: Average of 0.241 ppm, max of 0.8 ppm - Predatory Fish (Low on Food Chain):
-Salmon: Average of 0.014 ppm, max of 0.086 ppm
- Sardines: Average of 0.013 ppm
- Tilapia: Average of 0.013 ppm
Then what about the mercury content in commonly consumed meat?
- Meat:
- Beef: Generally between 0.001 ~ 0.005 ppm
- Pork: Generally between 0.001 ~ 0.004 ppm
- Chicken: Generally between 0.0001 ~ 0.002 ppm
- Lamb: Generally between 0.001 ~ 0.003 ppm
As you can see, the mercury content in large fish is noticeably higher. Furthermore, given how small cats are relative to humans, they are somewhat more likely to be affected by the ingredients and content within food and snacks meant for them.
Symptoms of Mercury Poisoning in Cats
Cats with mercury poisoning may exhibit the following symptoms:
- Nervous System: Loss of balance, lack of motor coordination, uncontrollable shaking, convulsions, paralysis, etc. In severe cases, it may even lead to seizures and heart attacks.
- Digestive System: Loss of appetite, vomiting, diarrhea, drooling, headaches, etc. Long-term mercury poisoning may even lead to dehydration.
- Kidneys: Mercury can cause damage to the kidneys, and in severe cases, lead to kidney disease. Affected cats may also exhibit symptoms such as frequent urination, blood in their urine, and increased thirst.
- Other various symptoms may include reduced vision, hearing loss, rashes and hair loss.
Research on the Effect of Mercury on the Kidneys
Much research has been conducted on the effect of mercury on the kidneys, leading to the following findings.
- Damage to Kidney Cells:
According to toxicity tests on the effect of mercury on kidney cells, mercury may induce mitochondrial dysfunction and cause excessive oxidative stress, resulting in damage to kidney cells. This damage, in turn, may impede the kidney’s ability to function.
- Accumulation of Mercury in Kidney Tissue:
Another research found that mercury can accumulate in kidney tissue, resulting in kidneys being unable to function properly. For instance, research conducted on residents near a mercury mine revealed that they had higher levels of serum creatinine and blood urea nitrogen, both of which are some of the most commonly used indicators of kidney functions.
Relationship between Tuna Consumption and Mercury Poisoning in Cats
This raises the question of whether cats can develop mercury poisoning from eating tuna. Research into this topic has already been conducted, and scientists have raised issues concerning the possibility of mercury poisoning.
- Research on Commercial Fish-based Pet Food
A study by the University of Nevada, Reno on the mercury concentrations in commercial pet food revealed that certain products exceeded the maximum recommended toleration levels of mercury concentrations. Researchers warned pet owners that the long-term feeding of fish-based cat food to their cats could put them at risk of mercury exposure.
- The Merck Veterinary Manual on Mercury Poisoning
According to the Merck Veterinary Manual, large fish such as tuna will accumulate large amounts of mercury within their bodies due to their feeding habits, and this may result in mercury poisoning in cats who consume them. Symptoms of mercury poisoning may include loss of appetite, vomiting, diarrhea, lethargy, shaking, convulsions, and irreparable damage to both the nervous system and the kidneys.
Why Are Cats with Feline Kidney Disease Vulnerable to Mercury Poisoning?
Cats with kidney disease are far more vulnerable to mercury poisoning than healthy cats for various reasons, but the main reason is that their decreased kidney functions can hinder their bodies from expelling the waste that has accumulated in their bodies.
- Reduced Kidney Functions: Cats with kidney disease have reduced kidney functions, which prevents them from effectively expelling the mercury that has accumulated within their kidneys.
- Kidney Damage and Heavy Metal Toxicity: When the kidneys are already damaged, mercury poisoning may cause further damage to the kidneys.
- Weakened Immune System: Kidney disease weakens a cat’s immunity, lowering their resistance to toxins and heavy metals.
- Nutritional Imbalance and Increased Toxicity: Cats with kidney disease suffer from a loss of appetite, and the ensuing nutritional imbalance reduces their ability to remove and expel toxins from their bodies.
Tuna can be a delicious and healthy protein source for cats and humans alike. It’s certainly a delightful treat for healthy cats who are not at risk of mercury poisoning. To such cats, tuna is a source of various proteins, making it ideal as an ingredient in both their food and snacks.
However, the story is different for cats with kidney disease, where even the slightest change can cause ripples in their health. If your cat has kidney disease, we urge you to be careful when feeding them tuna. If you absolutely must give tuna to your cat, please choose tuna-based products that are low in mercury, and call your veterinarian immediately if you suspect that your cat is showing symptoms of mercury poisoning.