I believe it is for nutritional reasons as the manufacturer states there are no preservatives or binders used (maybe they just mean gel binders?). But i'm no fish food expert but I did stay at a holiday inn express last night!
EDIT, from the website
Why is aloe vera in the food?
I started experimenting with aloe vera in my fish food formula when I learned of all the wonderful properties and abundance of vitamins, minerals and other beneficial substances that it contains. Some of the minerals found in aloe vera juice include calcium, sodium, iron, potassium, chromium, magnesium, manganese and zinc. It has Vitamins A, B1, B2, B6, B12, C and E, Folic Acid and Niacin. Aloe vera also contains amino acids and a rich supply of building materials that help to produce collagen an, essential protein found in all animals and specifically in fish scales.