A word of caution regarding fish-based dry (kibble) pet foods!
It seems that most pet food companies have exploded with fish varieties for dogs and cats. Salmon, sardine, mackeral, haddock and other varieties of whitefish to name a few. Many people think that pets with food allergies are less likely to have a problem with fish-based foods than with chicken or other protein sources. While this may be true for some pets, there is definitely a down-side with consistently feeding fish-based foods.
First of all, there is a huge concern with the level of contamination currently in our oceans, which means that it is not really a good idea for anyone (person or pet) to eat a diet that is based on daily consumption of fish (unless perhaps you live in a remote area of the world and are catching your own fish and eating a variety of different seafoods). Secondly, there are specific chemical preservatives that are used to preserve fish meal to be used in pet foods, and these toxins add up over time; especially when pets eat fish based food every day for months to years.
You may have heard of some common food preservatives such as BHA & BHT, which should definitely be avoided, as they are known carcinogens (cancer-causing). However, few people have heard of Ethoxyquin, the chemical typically used to preserve fish in pet food diets. Chemical preservatives can build up to toxic levels in the body when they are consumed regularly over time, even if the amount per meal is determined to be “safe” or below toxic levels. Furthermore, Ethoxyquin has been linked to kidney disease and kidney failure in pets, in addition to its carcinogenic potential.
A very important and misleading fact about pet foods containing Ethoxyquin- is that this chemical preservative is often added to the fish or fish meal prior to its delivery to the pet food manufacturing plants. In this (very typical) scenario, pet food companies do not list Ethoxyquin in the ingredient panel on the bag, so most consumers do not know that their pets are ingesting these toxins in their food.
As a general rule, I recommend avoiding dry food diets to opt for fresher sources of pet food which include fresh-frozen raw, freeze-dried raw, air dried, dehydrated raw, or home-cooked, if done correctly, with balanced nutrients and supplements.
If you do choose to feed dry food, I definitely caution against consistently feeding exclusively fish-based diets. It is much better for most pets to be eating a variety of protein sources, not only for improved all-around nutrition, but also to help avoid heavier levels of unwanted additives in certain types of foods.