The short answer, with the conditions attached
Yes, a kitten can eat tuna canned in spring water, in a small amount, as an occasional extra. Of the tuna options on a shelf, spring water is the kindest choice for a kitten: the fish is packed without added oil, which keeps it leaner, and without the salt load that comes with brine. Offer it drained and plainly flaked, with nothing seasoned, smoked, or mixed with sauces, and treat it as a garnish on the day rather than a portion in its own right.
Those conditions are the answer, not fine print. The same food offered daily, in quantity, or instead of kitten food creates problems that a teaspoon as a treat never will.
Why tuna cannot feed a growing kitten
A kitten is building bone, muscle, eyes, and brain at speed, and that construction runs on complete kitten food, which is balanced to supply the amino acids, fats, vitamins, and minerals growth requires in the right proportions. Tuna alone does not provide that balance. Fed as a main food, it leaves gaps, including nutrients cats cannot make for themselves and must get from a properly formulated diet, and it delivers other elements in proportions a small body does not need day after day.
There are two further reasons to keep tuna occasional. Fish-heavy feeding exposes a cat to mercury that accumulates with frequency, which matters more for a tiny kitten eating regularly than for an adult having a rare taste. And tuna's powerful smell and flavour can train fussiness: kittens that learn meals taste like tuna may start refusing the complete food they actually need, turning a treat into a standoff at every bowl.
Serving it sensibly
Keep the amount small, a little flaked tuna pressed onto or beside the usual kitten meal, and keep the frequency low, an occasional novelty rather than a standing appointment. Drain the spring water away rather than pouring it over the meal regularly, since the liquid carries the fishy flavour and some salt with none of the nutrition your kitten needs.
Introduce any new food, tuna included, in a tiny first taste and watch the litter tray and the kitten's comfort over the following day. A soft stool, vomiting, itching, or a kitten that goes off its normal food after trying fish is a reason to drop tuna from the treat list and, if signs persist or the kitten seems unwell, to contact your vet for advice about that specific reaction.
Better ways to use a kitten's treat allowance
If your aim is bonding and training rather than tuna itself, complete kitten treats and small pieces of simply cooked plain meat or fish give the same hand-fed pleasure without teaching the kitten to hold out for one overpowering flavour. Rotate tiny extras instead of repeating a favourite, use treats to reward litter tray success and handling practice, and count them within the day's food rather than adding endlessly on top, because kittens gain condition quietly and early habits around food tend to stick for life.
Keeping every feeder on the same page
In a household where several people feed one kitten, treat drift is the usual failure: each person adds a little tuna, and the kitten quietly eats fish all day while its complete food goes untouched. Agree who feeds, what counts as a treat, and how often tuna appears, and write it into the kitten's routine where everyone can see it, which is where KinsLe helps through Care Teams, assigning feeding duties to each person and time-stamping completed tasks so a kitten's tuna stays the rare treat it should be.