Although your cat would probably love nothing more than to eat tuna all the time, a high-fish diet isn't compatible with proper cat nutrition.
I'd like to share some information on cat nutrition as requested by a reader. I've been a long-time feline fancier and a subscriber to various magazines devoted to the animals. Add to that the reading of numerous books and talks with my vets—including the recently deceased Dr. Les Colette, who wrote the medical column for Cats Magazine—and you have someone who hopes she knows a little about the subject.
I used to make complicated concoctions for my pets to insure their good health, and one of the ingredients I used was dry milk. My advice is: Don't! Over a period of time I noticed that the cats would have loose stools and diarrhea, especially if I increased the amount of milk powder over a period of days to 1/3 cup per animal. Other breeders I spoke with confirmed my observation. According to what I've read, some adult cats can tolerate milk, but some, if not most, can't digest it properly—just like some people. To be on the safe—and healthy—side, don't give this food, either fresh or dried, to grown felines.
Another point: Fish is not a natural food for cats and I strongly caution against its overuse! The animals can become almost addicted to it and refuse anything else. This has happened to three cats that belong to a neighbor of mine. Two are able to tolerate a high-fish diet, but the one that is not has become afflicted with skin problems and loss of hair. Now the owner is stuck with a "problem" pet, since her cat won't eat other foods and she can't bear to go through the difficult period of getting it to accept alternate fare.
Another error people make in the belief that they're upgrading their cats' nutrition is to feed them eggs. Whole eggs. Again, don't. The yolk is OK, but the white blocks the absorption of important nutrients in the intestine. Be thrifty: Give the yolk to Puss and add the white to your breakfast eggs.
Many people are unaware that fats are important in the feline diet. A daily teaspoon of butter or oil (not fish oil) is a very good idea. Got fat scraps from steak or other meat? Rinse off the seasonings and chop the pieces into the animals' food. Cats, unlike humans, need saturated fat—especially if you rely heavily on canned or dry commercial rations, which (to retard spoilage) contain very little of this necessary ingredient.
In the wild state, a cat usually eats most of its prey, including the contents of the intestine. If your felines are indoor pets, as mine are, provide a pot of grass for them to nibble instead.
And that brings up the question of vitamin C, which was long considered an unnecessary additive for felines because the animals produce it in their bodies. Illness or disease, however, can quickly deplete a cat's capacity to manufacture enough of this very essential substance. I recommend that a good supplement with vitamin C and minerals be added to the daily diet, no matter what it is. Control your pet's intake of vitamins A and D, which are toxic in large doses. (The same rule applies to people.)
If you use canned food, as I do, read that label! Some unscrupulous manufacturers make incomplete rations that can kill kittens if they're fed exclusively on the one brand. Use only those tinned foods that are described on the can as complete and balanced. Almost all such products contain fish, by the way, so don't add more.
Unfortunately, I'm not familiar with the possible ill effects of bone meal on cats. Here's my philosophy, though: If there's any doubt about the safety of an ingredient, don't use it. There are safe and established methods of feeding the creatures and it shouldn't be necessary to experiment with your pet.
Here's a sample diet which I find healthy and practical to feed to my eight cats. The basis is a balanced canned food (Friskies, Puss 'n Boots), a dry ration (Purina) and a vitamin and mineral supplement. To this I add cottage cheese (sparingly); bacon drippings—again sparingly, because of the high salt content—or oil or butter; unseasoned meat broth from chicken backs, necks and skin, steak bones, etc.; egg yolks; chopped leftover meats and fat; liver occasionally; wheat germ ... whatever I have on hand. It isn't necessary to make exotic mixtures. For kittens I combine strained baby meats and cottage cheese as an extra feeding.
I could go on and on. If you feed your cats raw meat, check them for worms twice a year. Provide some dry food: It cleans the teeth, just as bones clean the teeth of wild felines. Don't give your pets a monotonous diet—variety is the spice of life and health—and don't overfeed them.
Take your animals to the vet if they start ailing (preferably at the first sign). Have him check out any physical problem, and don't depend on home remedies or neighborly advice unless you or your neighbor are thoroughly grounded in feline physiology and health care. Cats are not like people or dogs. They are unique. New facts are being discovered all the time. You'd be surprised how many veterinarians are great with dogs, horses, and cows but don't know their cats!
Incidentally, if you must doctor your pet at home, don't use aspirin. It's very poisonous to cats.
Read up on feline health, body functions, nutrition, etc., just as you do for farm livestock. Care for cats with knowledge, common sense, and love, and they'll reward you with many years of companionship.
Cat lovers will find the following magazines entertaining and full of up-to-date information:
 Cats Magazine. Special eight-month subscriptions are available for $3.50. This is the most comprehensive of the three publications.
 Cat Fancy. Eight issues $6.95, 16 issues $12.95. For the general reader.
 Siamese News Quarterly. (Volume XIV, Nos. 3 and 4 contain nutritional information.)