The zoo writes about it on 13 February 2020 (translated):
UNIQUE VEGAN FOOD FOR FISH IN BLIJDORP
Herbivorous fish in aquariums are fed worldwide with fish feed with animal ingredients. There must be another way, thought Blijdorp. The zoo took action and is now developing its own, more natural diet for the herbivorous marine fish in the Oceanium. Everything is aimed at improving the welfare of the animals.
Ingredients fish food
The existing fish food of marine fish differs greatly from the diet of their species in the wild. All over the world they receive food of mainly animal origin, such as fishmeal. The plant-based ingredients in these foods are grown on land and not in the sea, such as corn, grain, soybeans and other beans. That’s pretty strange. There is a suspicion that this “unnatural” food is the cause of various fish diseases. An adequate diet could at least suppress various fish diseases such as marine head and lateral line erosion. That is why a new feed is being developed in the Oceanium.
100% vegan from the sea
Animal and farmed products are omitted from this new, natural feed. It only consists of vegetable products from the sea. With this, not one but more steps are taken in the right direction. After all, avoiding the use of soy also protects the Amazon region.
Most herbivorous fish are “grazers”. For example, surgeonfish (known as Dory from the Disney movie) eat algae that grow on the hard surface of reefs. This natural grazing behaviour is also stimulated in the Oceanium. The new fish feed is not bound with the usual gelatin of animal origin but with agar made from red and brown algae. This is spread over our artificial corals in liquid form. This gives the fish the chance to show their natural grazing behavior. For the other fish in these aquariums it is more difficult to eat with this because their mouths are unsuitable for scraping or pulling away the food. In this way only the herbivorous fish can eat it. Now they can graze longer, just like they do in nature.