Tuna should only be given a s an occasional treat.
As for feeding him dry only... Let me share with you what I have learned about feline nutrition to help you make an informed decision on what diet you should feed your cats.
Many brands of manufactured cat foods claiming to be "healthy" really are not. In fact they are made of the lowest ingredients possible. I'm not saying that a cat can't live off them... just the same as you could live off hot dogs and Mac and cheese forever, but better choices can and should be made for your feline friends. I would not venture to say that any manufactured food is "best" for a cat but a grain free organic wet food would be a good start. Feeding canned is certainly better than feeding dry in all cases.
Cats were never meant to eat dry food, also known as cereals or kibble. We, humans, make them eat it for convenience to us. It has nothing to do with them or their nutritional needs. It's completely species inappropriate.
In the wild, cats derive their entire liquid intake from their prey. They do not have a thirst mechanism because they don't need it when eating a species appropriate diet. They get all they need from what they eat. So they do not drink water. Regular ol' house cats have descended from those same wild cats.
So in a home environment, your kitty does not get the moisture it needs from dry food and it’s almost always in a constant state of dehydration. Water fountains are encouraged to TRY to get your cat to drink more and your kitty may even enjoy it, but it will never meet its water intake needs drinking from a bowl.
Deadly feline illnesses such as diabetes, kidney failure, obesity, Irritable Bowel Disease (IBD), bladder stones, kidney stones, urinary tract blockages and Urinary Tract Infections (FLUTD), with and without deadly crystals run rampant these days. Cats are not taking in enough water to stave them off. Proper water intake through a species appropriate diet alone can prevent most of these conditions.
Overall, wet is all around better for any cats diet, be it canned or Raw and they should never be fed dry cereal kibble if we wish to most closely match their wild nutritional and dietary needs. Kibble meets our needs… not our cats.
It is also bogus that kibble cleans teeth. DRY FOOD DOES NOT CLEAN TEETH. It's an old myth that has been scientifically disproved for years, but old-school vets drilled it into people's heads for so long (and sadly still do) that people still believe it. Cats can not “chew”. They do not have flat “chewing” teeth. Their molars are not for grinding food. They have meat ripping pointy carnivorous teeth. You may see them “crunch” a piece of food once to crack and break it… but they are absolutely unable to chew a hard piece of food. Want your cat to have clean teeth? Give them an appropriately sized raw bone. :o)
I personally feed a Raw Meat and Bones based diet to my cats and they are very healthy on it. I HIGHLY recommend it. Once I got the hang of it and felt comfortable with it it's a snap to prepare. It's something you might want to consider someday. Cats are obligate carnivores after all and must derive ALL their nutrients from meat based sources. They are unable to absorb them from any other source. Despite thousands of years of domestication they remain strictly carnivorous. True and honest meat eaters and that is what they need most. Protein from meat!
If you are interested in feeding a raw diet some great places to start learning are http://www.catinfo.org/ , http://www.catnutrition.org/ , and http://www.felinefuture.com/nutrition/ .
If you would like to try raw with your cats and don’t want to get all technical about it but want to try a trusted, time tested and balanced raw diet you can order from http://www.felinespride.com/products/catfood.aspx . I purchased this myself when I first started and my cats loved it!
Another premade Raw you can try is Natures Varity. I personally have never used this but know many people that do and it’s pretty easy to find http://www.naturesvariety.com/content.lasso?page=1507&-session=naturesvariety:D04EC9250597c11908GJS417647E.
If raw is not an option for you please be aware that there are three Categories of manufactured Pet Foods:
-"Grocery store" foods – (Generic Brands and cheap name brands) Those foods found in grocery stores and mass-market retailers are made with lower-quality, less-digestible, inexpensive ingredients and are therefore a cheaper alternative. While easy on the pocketbook, "grocery store" foods normally do not provide your cat with the healthiest, most nutrient-dense ingredients.
-Premium foods – (Iams/Eukanuba, Purina One, Hills Science Diet, Nutro and such) Foods often found in grocery stores, pet stores, and veterinarian offices that contain higher-grade ingredients, but still include many elements of "grocery store" food, such as artificial colors, artificial flavors, chemical preservatives, and "filler" ingredients such as corn and wheat products, by-products and even animal digest. Yuck! Premium foods are usually more expensive than "grocery store" foods because their ingredients are sometimes of a higher quality, and are therefore somewhat more beneficial and digestible. But don’t be fooled, some of those same so called Premium brands are sometimes worse than grocery store foods, but they charge prices like they are better. They aren’t!
-Healthy foods – (Wellness, Merrick, Eagle Pack, Drs Foster & Smith) The newest addition to the pet food market - provide pets with the highest quality, healthiest, and most nutritious ingredients. They are typically available for purchase online or direct from the manufacturer. Some better retailers are starting to carry them now. Complete Petmart carries a few healthy brand foods. Foods in the Healthy class contain nutrient-rich ingredients. Formulated to provide optimum health benefits for pets, these foods often use real meat as the primary protein source, carbohydrate-rich whole grains like brown rice and barley and whole, fresh fruits and vegetables. They should not contain artificial preservatives, flavors, or colors. They will almost always be fortified with additional vitamins and minerals, and will use the best natural sources for fatty acids to help build healthy skin and a beautiful coat. Because healthy foods use high quality ingredients, you should expect to pay a little more than you would for other types of pet food. Remember, though, with healthy foods you can feed less since healthy foods are more nutrient-dense than other types of food so it often evens out or cost’s les than feeding foods filled with cheap non-nutritional by-products fillers.
With all that information in mind, when you are choosing a new cat food, study the ingredients. All ingredients on pet food labels are listed by weight. Meaning whatever ingredients are listed first on the list, there is more in there. The first ingredients listed should be whole meat ingredients, protein sources, such as Chicken or Turkey. NOT just the word “meat”! Who the heck knows what that is? The word Chicken Meal is ok, but it should be a secondary ingredient, not first. Meal is the meat dehydrated and ground into a powder.
The ingredients also should NOT include any by-products or animal digest whatsoever. Those are disgusting left over animal parts that are scraped off the filthy floors of meat and poultry plants. They should just go into the trash but they put them into pet food instead. EW!!!! Also make sure there are no artificial colors or flavors. And make sure there is no BHA and BHT used preservatives. These preservatives have been shown to cause cancer in both cats and dogs. Bad Bad stuff and it’s in almost every cat treat on the market. :(
So, in summery of the ingredients… if you see the words by-products, Animal Digest, the word “meat” alone, Corn, Corn Gluten, Wheat Gluten, or BHA or BHT… stop reading, put down that product and move on to the next.
Be aware that when switching to a Healthy, Holistic or Organic food, you will pay for what you get. Good foods are not cheap. They are pricey and will cost you more than cheaper products, just like steak costs more than hotdogs. But again, you will be feeding a better food and improving the over all health of your pet. This in turn leads to less vet visits for illness now and more importantly later in life in their geriatric years. You will also feed less of this food on a per animal basis because a smaller amount of food contains what your cat needs. Overall healthy wet foods are well worth it, if only for the piece of mind that the ingredients are better for your cat than cheap crap.
You can start your research for a healthy cat food here if you are not ready to try feeding a Raw diet:
http://www.onlynaturalpet.com
If you want to buy in a store, Complete Petmart is a good store and carries quite a few natural, organic, and holistic blends. Also check with your local feed/grain stores.
I highly recommend you take the time to research for yourself, but the information I have given should get you off to a good start. Good luck choosing a new healthy food!
********IMPORTANT*******Don’t forget to switch your Pets food slowly over a period of 10 to 14 days, if you can. Mixing 25% new to 75% old. Then 50/50… then 75% new to 25% old. And finally switch over to 100% new. Take it slow as not to upset their digestive system.
Side note… Please don’t feed Iams / Eukanuba. It’s ALL fillers, byproducts, animal digest and CRAP. Read the ingredients! There is nothing good for your cat in that food. Not to mention they conduct the most appalling animal testing you have ever seen. http://www.iamscruelty.com to see the terror they create.