Why one anchovy is fine and a habit is not
Anchovies are small oily fish, and in themselves they carry the same fish oils and protein that make oily fish a useful part of many dogs' diets. Nothing in a plain anchovy is toxic to dogs. What changes the picture is how anchovies reach a pizza: they are cured in salt or packed in brine or oil, then baked on top of a salty, cheesy, seasoned base, picking up extra oil and flavouring as they cook. A single fish is a trace amount of all that. A regular scattering, or the whole leftover portion an owner might tip into a bowl, is a salt load a dog's body did not evolve to handle at once.
Preparing the pizza anchovy before it reaches him
Lift the anchovy off the pizza and run it briefly under the tap, which takes off surface brine, pizza grease, and any loose cheese or tomato sauce clinging to it — the sauce may contain onion or garlic seasoning he does not need. Pat it dry and offer just the fish, not the crust corner it sat on. If your household orders anchovies canned in oil for cooking instead, the same logic applies: one fish, drained well and rinsed, as an occasional curiosity rather than an ingredient in his meals. Fresh or plainly cooked anchovy, when it is available, is the cleanest version of all, served boneless in the tiny quantity these little fish naturally come in.
Salt is the real portion limit here
Think of the portion question for anchovies as a salt question, not a fish question, and one small fish is where the answer lands for any size of dog. Afterwards, make sure his water bowl is full and fresh, because a salty bite makes a dog drink, and drinking is exactly how his body sorts the salt out. Watch for the signs that salt did not agree with him — unusual thirst that does not settle, vomiting, wobbly unsteadiness, or diarrhoea — and call your vet promptly if you see them, particularly in a small dog, for whom one fish is proportionally a bigger dose. Repeated vomiting or tremors after any very salty food should be treated as urgent.
Dogs who should not get the anchovy at all
Skip this particular treat entirely if your dog has heart disease, kidney problems, high blood pressure being managed by your vet, or a prescribed low-salt diet, because for those dogs there is no sensible occasional exception — the salt is the very thing their diet is controlling. Puppies, too, are better given plainer treats while their systems are still developing. For these dogs, the pizza-night ritual can still include them: set aside a small piece of something from his own food before the boxes open, and let that be his share of the occasion.
Turning pizza night into a managed ritual instead of a scrounge
Dogs learn pizza night fast, and the appealing smell of anchovy makes begging at the table intense if it is sometimes rewarded. Decide the household rule before the box opens — one rinsed fish, given in his bowl away from the table, or nothing at all — and stick to it, because negotiating at the table teaches him that persistence upgrades the portion. Clear plates and the pizza box promptly, since a determined dog left alone with leftover slices will help himself to far more salt, fat, cheese, and crust than the single fish you intended.
Recording the one-off so it stays a one-off
The difference between a harmless single anchovy and an accidental habit is usually just memory: someone forgets he had one last time, or two people each give him one on the same night. Noting the treat in his KinsLe Care Teams feeding duties, with the completed task showing when he had it, keeps the family's pizza-night rule honest and stops one fish quietly becoming his standing order.