Yup. another factor could be genetics OR the dominant one is simply eating more food by getting to it first. But don't be tricked by baby size...the red could ultimately be bigger than the tiger. It happens. Their true personalities won't kick in until later.Well it could also be a dominance thing, usually I find that subordinate fish don’t put on size as quickly as more dominant ones. Stress plays a factor in growth imo.
The red might be younger, too.