Dog food companies are constantly producing new flavors of dog food. One thing that doesn’t change as frequently, however, is the main protein source within the food. Many dogs are sensitive or 'allergic' to beef and chicken which results in owners serving their dog a food with fish as the main protein source instead. Since more dogs are receiving fish in their diets, it is only the natural progression of things that more and more dogs are being diagnosed with an allergy to fish. It is still rare to have a dog with a fish allergy, but it is becoming more common by the day. If your dog has ongoing vomiting and diarrhoea, or is constantly scratching, licking, or getting an ear infection repeatedly, you might want to consider the possibility of it being caused by a food allergy. If it is discovered fish is the culprit, as soon as you remove it from your dog’s diet, he should recover very smoothly and all symptoms of allergies should stop once it is out of his system. Keep in mind though, that many dogs with food sensitivities are sensitive to more than one ingredient. Similarly, these dogs are more prone to environmental allergies, so it is common for some symptoms to persist, even if they improve with diet modification.

Many dog foods have fish as their main protein source or as an ingredient of some sort. If you have your dog on a diet containing fish and he is acting abnormally or suffering allergy-like symptoms, be sure to consult with your veterinarian.

Symptoms of fish allergies in dogs may appear quickly once he starts eating a diet consisting of it, but in other cases the allergy may take months or years to develop. Allergies typically present between the ages of 1 and 5. Symptoms of fish allergies may include

A life-threatening allergic reaction such as anaphylactic shock is rare but possible. If the allergy is severe enough, your dog will go into anaphylactic shock immediately after ingestion. If this happens, it is a medical emergency and your dog needs to be seen by a veterinarian immediately.

The terms ‘fish’ and ‘fish derivatives’ found on dog food labels are very broad. These terms come with a lot of criticism, but it does not mean that the quality is bad. The terms can vary due to certain countries having laws and customs that may not allow something more specific. 

In other cases, using a broad term allows the species of fish in the food to be altered without having to change the bag. As seasons change and overfishing occurs, dog food companies may change the species of fish they are using in their food, but since it is listed as ‘fish’ they do not have to change the bag.

If your dog has allergies, it is his body’s way of protecting itself from something it thinks will harm it. While the item in question is actually harmless, the body doesn’t recognize it as such. The body finds it dangerous and mounts a protective response to the threat. Your dog’s body produces an immune response to the fish ingredient. This allergic response may develop quickly or may develop over a period of years. Many food-related allergies happen after the dog suffers from an infection involving the stomach or intestines. 

Since many dogs have allergies to other protein sources such as beef and chicken, fish is becoming one of the more popular protein sources in dog foods. As a result, more dogs are developing an allergy to fish which means one less protein source you can safely feed your dog. However, there are some foods that specify the species of fish they are using. By feeding your dog one of these foods, you know exactly what you are feeding him, and if he develops an allergy to one specific fish, you can potentially try him on another. Take note; If sensitive to one type, it is not uncommon to be sensitive to all types. Those with food allergies tend to benefit most from a hypoallergenic diet.

Intradermal skin testing for food allergies may not give an accurate diagnosis in every dog. This test can give false positive and false negative results. In a false positive situation, despite the fact the dog is not allergic to the food when ingested, it results in a positive allergic skin response. As for a false negative, some food allergies produce a delayed result of a positive allergic reaction. This causes the veterinarian to believe your dog is not allergic to the allergen since she didn’t see a skin response, but in reality, he is allergic to it. 

Serology can be run to check for antibody levels. As with intradermal testing, results aren't always accurate but it can be helpful.

Bicom testing is an unproven method that claims to be able to detect allergies, which you may have heard of. Bicom testing is also known as bioresonance. This method believes every being and substance in the world emits its own electromagnetic wave. The veterinarian takes a blood sample from your dog and tests different food items and substances to see if it has a ‘good’, ‘neutral’ or ‘bad’ response. If the response is ‘bad’, the item being tested causes your dog’s blood wavelength to become stressed. Stressed blood leads to a stressed body and therefore an allergic reaction. If the response is ‘good’, then the item puts out a wavelength that is compatible with your dog’s blood which means no adverse reactions should occur. If it is ‘neutral’, the item being tested does not put out a wavelength that alters that of your dog. Most vets will not offer this service as there is no data which backs it up.

A dietary trial is the most frequently used method of diagnosis. In a dietary trial, you have to feed your dog a novel diet, meaning you feed him a diet without any fish ingredients whatsoever. During this trial, you cannot give any type of treats containing fish or fish flavored medications as it can affect the results. You have to feed your dog the novel diet for at least 90 days before you can get a reliable diagnostic. After the 90 days, if resolution of the allergic symptoms occurs, you then must reintroduce fish to his diet. If a relapse in allergy symptoms occurs once the fish is reintroduced, then you know the source. If symptoms do not return with the reintroduction of fish, then it was a source other than the fish your dog was reacting to.

Strict control of the diet is the best treatment of fish related allergies. It can be a long, discouraging process, but once you discover the source of allergen and are able to successfully remove it from his diet, you and your dog will both be better off. Removing fish completely will also help avoid chronic infections. If the allergen remains in your dog’s food, it will continue to weaken his immune system over time. This leads to long-term and recurring issues. Not only will you both be miserable, but it may also result in much additional veterinary care expense.

As a fish allergy alone is rare and most dogs are allergic to several foods, a hydrolysed diet is the best one to trial. Proteins are broken down and animals do not react to food given in this manner.

Some veterinarians will prescribe a medication to help with the itching your dog may be suffering from. This medication will help for a while, but in reality it is only masking the symptom, not curing it. If you do not remove the source of the itching, you will have to continue to give the prescription and possibly continuously increase the dose as time goes on. If your dog has a more serious reaction to the fish, such as respiratory issues or anaphylactic shock, seek veterinary care immediately.

Once you remove fish from your dog’s diet, the symptoms should subside in time. It may be several weeks before you see any serious improvements. If your dog has a serious reaction, such as anaphylactic shock, the sooner you seek veterinary care, the better off he will be. If you do not get him veterinary care, he may die.

Since fish is still considered a ‘new’ protein source, not many dogs are allergic to it yet. If you suspect your dog is one of the few allergic to it, discuss it with your veterinarian. The two of you will come up with a diet plan suitable to your lifestyle and his dietary needs.