Tuna-based pet foods make up about 5 percent of canned pet foods, and a surfeit of formulations exist. The tuna used may or may not be human-grade; though it usually is in upscale gourmet lines. Dark muscle meat, byproducts, chemically altered fish protein and even endangered tuna species are used in cat foods.
Dark Muscle Meat
Dark muscle meat, also known as blood meat, contributes about 12 percent of tuna caught to produce canned foods, and it's the main ingredient in tuna-based pet foods. The blood meat has a strong flavor that may be appealing to cats, but blood meat is generally trimmed from canning tuna, as there's little demand for it in the human food marketplace. Depending on the grade of cat food, the muscle meat may or may not be human-grade.
Fish Protein Hydrolysate
Fish protein hydrolysate is fish protein broken down through a chemical process to change the chemistry of the protein's peptide bonds. Industries like this process because it is simple and inexpensive and creates a stable product with variable chemical composition and functionality. However, such chemically altered products have limited nutritional integrity and are highly salty. Therefore, they are used generally in flavor enhancers and pet foods.
Controversy has surrounded the use of endangered bluefin tuna in some cat foods. The Mars company received criticism from Greenpeace and other organizations for their use of bluefin-tuna-flavored cat food. The company stated it intends to use only sustainably sourced fish by 2020 and is phasing out the bluefin-tuna-flavored food, replacing with an albacore-flavored product. Greenpeace member Willie Mackenzie replied that bluefin tuna may be extinct by 2020 and that more-rapid progress must be made.
Since tuna's white muscle meat is the most sought part of the fish, many parts are considered waste products, also known as byproducts. These include the skin, bones, fat, organs and other parts of the fish that are not in demand. Although these parts of the fish do contain some protein and fat, they have no commercial value. Therefore, they are used to make other products including fish oil, fish meal, fertilizer, gelatin and pet foods. In general, foods with byproducts are less healthy than those without.
Sarah Whitman's work has been featured in newspapers, magazines, websites and informational booklets. She is currently pursuing a master's degree in nutrition, and her projects feature nutrition and cooking, whole foods, supplements and organics. She also specializes in companion animal health, encouraging the use of whole foods, supplements and other holistic approaches to pet care.