Enormous cardinal tetras at the Vancouver Aquarium

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I was at the Vancouver (public) Aquarium a week or two ago. They had a tank full of enormous cardinal tetras, twice the size of any cardinal tetras I have seen anywhere else. I am not sure if they received them this size to start with or if they raised them to this size. I am looking at overfeeding my cardinals to achieve the same results maybe with a mix of live and frozen food. If anyone has seen or raised similar monster cardinal tetras any tips on this.