Veterinary science is more practical for a professional career but it takes longer than Aquaculture. Vet take 4? years of study, whereas aquaculture is 2 years.
Vet science covers a wide range of animals, birds and fish, and includes general care, diseases and surgery. Fish health is briefly covered but further study is required to be a fish health specialist.
Aquaculture covers the care and keeping of farmed food fishes (not aquarium fish), and sometimes covers diseases, but it doesn't cover surgery or any other species of animal.
If you have a choice, go for vet sciences and then study aquaculture after or even while you are studying vet science. Aquaculture can be done easily any time but vet science needs you to focus on the subject.
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I haven't officially studied anything and am self taught. I read books and worked in pet shops and learnt about fish and diseases the hard way.
ANGFA is the Australian New Guinea Fishes Association and consists of scientists and hobbyists that keep native freshwater fishes from Australia and New Guinea. It's basically a fish club that specialises in rainbowfishes and a few other natives fishes. It doesn't have much to do with diseases but is interesting if you like rainbowfish.
There's more info about ANGFA at the following link.
The Australian and New Guinea Fishes Association - ANGFA
www.angfa.org.au