Yes it is best to defrost the food before feeding to goldfish, or fish in general, it's easier for the fish to eat it and they will not become "chilled" by eating the food if it is already defrosted.
There are vitamin products made specifically for fish. I use Vita-Chem freshwater version for my freshwater fish. It is used to soak the fish food in before feeding them to the fish.
No, because it can be poisonous to the fish and they will eventually die. So, I recommend feeding them fish food.
Lots of food.
The gill rakers on fish keep food particles from moving out from in between the gill arches. For filter feeding fish and some suspension feeding fish, the gill rakers function is to trap the food.
it depends on the fish you have. if you have a community, then obey the suggested feeding schedule on the food.
once their "food sacs" are gone you should probably start feeding them one or 2 day later
This may mean that you are over feeding your fish and they cannot finish what you have put in the tank; reduce the amount of food you give each feeding, and make sure you clean the tank regularly
Hand feeding a fish means that you train your fish to take their food from your hands. This is something that many fish keepers do, and you will always want to start off by letting the fish get used to seeing your hands in the tank, then gradually work your way up to being able to get them to take food from you.
Different species of fish need different foods and find/capture their food in many different ways.
Depending on the fish, all fish have different requirements for the feeding For eg. I have a gold fish who I give a pinch of fish food once or twice a day.
1) The species of fish in the pond. 2)The type of food the fish are usually fed. 3)The last time the fish were fed. 4)The next time the fish would/should be fed
take it to the vet make sure you are feeding your fish the right food aswell and enough food but still take it to the vet