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ıf they are independent from each other, yes you can assuming you are using between subjects ANOVA.

Yes. The factor is species (qualitative factor) with different levels and each species is a level. But the levels must be independent.

Yes ,you can do. If you have fish of different size, different species and different age group. But as such for a case you can't do the factorial. If you have only one species you can either do one way ANOVA or you can follow GLM to get a clear picture of your data. 

Yes, you can do