The picture shows the egg packages of mosquito Culex pipiens. They are found in water barrels. It can also be seen the small hatched mosquito larvae.
It is a very good feed for young fish.
Insect larvae and drowned insects are the normal feed in the tropics.
I take this opportunity each summer.
It does no harm.
Other mosquito larvae are produced in hatcheries (Singapore). If alive sent by plane. Genus Cironomus. Have a red color and the mosquitoes can not bite.