Fish feeds on a lot of things. However, to get the best from them especially when raised in commercial quantity, one must give them feeds that are well compounded and rich in all necessary classes of food. Thus, I will categorize fish feeds into imported, local and others.
Imported feeds are those feeds that are already bagged and imported into the country. They are mostly floating pellets and are into different sizes like 2mm, 3mm, 4mm, 6mm etc. which are fed into the fish based on their age and sizes.
Local feeds are those prepared by sourcing for the ingredients locally, compounding them and forming them into pellets. They are usually sinking pellets and are of various sizes as well. Others are feeds like maggots, biscuits remnants, spoiled breads etc.
Meanwhile it is advisable to feed the fish on imported feeds for some time if at all local feeds will be introduced. This is because imported feeds are richer and easily picked up by fingerlings and juveniles than local feeds.
Imported feeds will make them develop very rapidly, after some time, feeding them solely on local feeds or mixing with imported will not cause any harm to the fish.
As for questions like: when is it advisable to change their feeds from imported to local? Well, if they are well fed from the onset, I normally recommend change from imported to local at the age of 2months (i.e. from juvenile stage).
However, the feeds could be changed earlier if they have a rapid growth. For instance, if they weigh around 300grams even before 2months, then, the feed could be changed. It is however advisable that you don’t change the feed sharply. It is better to mix both imported and local for like 2weeks before changing to local only.