If you are keeping only Swans (no ducks or geese in same space)... Feeding is very easy, they moderate their eating and you can (and should) keep food available 24/7...
Our diet for our 2 black swans:
Everyday:
- A LOT of salad(s) and all kind of "green leafs" (always available)
- Sliced cucumbers (we give 4 big cucumbers per day, we peel them and give the peels separately)
- Few crushed tomatoes (slice the tomato in 2 or 4 pieces, and then just "crush" by hand so its easier to eat)
- Duck pellets / granules... These might need to be moderated if they go insane with them, our girls arent so fond of these so we keep these always available too.
In addition (changing "menu")
- Peas, Corn, Carrots, Potatoes (not raw)... These are easy to buy frozen, if you buy a mix that have potatoes, the potatoes are always "half cooked" and ok for swans straight from the bag.
- shredded carrots, shredded pumpkins
- Almost all kind of edible berries, these we give very rarely, tend to be very expensive

... But if you can get good healthy berries for cheap, thats a great addition to even daily diet.
Treats
- Mango, Papaya, Apple, All kind of melons, Oranges... They love fruits, but its not good in their daily diet. We give a bigger portion of fruits to them maybe once a week, few pieces per day would work too of course.
And what goes to the fish, Swans are opportunist eaters, they will eat fish if they can catch it and its small enough. BUT they dont need the animal protein and you should never offer them any meat(s). If they catch few bugs, small lizzard or something like that by themselves, its ok and wont hurt them, but its bad diet for them.
In wild Swans can eat 4kg (8-9lbs) per day, but of course in wild they also use a lot more energy vs in captivity. Our Black Swan girls seem to eat around 4kg (8-9lbs) total in day, They have around 5kg of food available and there is always something remaining after 24h. But this is up to individuals, species, their size etc, you need to test this by yourself... Start by giving A LOT of food and then reducing the amount daily until there is always something remaining when you give their next food in 24h.
Amount of food needed varies a bit by the time of year too, while they are molding they eat a big more. And i would imagine if you have a Male+Female pair, they would eat quite a lot more when they go hormonal. Our Female+Female pair goes hormonal too, but of course not that "bad" as they would if they were Female+Male.
One more point, we use these big "dish bowls" as their cups, and wont feed them in their pond... Eating in water (pond) is the natural way for them, BUT if you do that... You will be changing the water DAILY, no amount of filtration can deal that, you would need industrial water purification plant for the amount of poop and pieces of food =)
Getting them eat "on ground" wasnt hard at all, they just accepted it immediately and with this, we can change the water "only" once a week.
View attachment 4045073
View attachment 4045067