Formula is now supposed to have LCPs (AA and DHA, or Omega 3 and Omega 6 as they also get called) as it was shown a few years ago that this made a difference to babies intelligence and is naturally occurring in breastmilk. Aptamil had it in before the research was done and it was recommended for all formulas, which is how they got the reputation of being closest to breastmilk, which is no longer true as all formulas now have LCPs.
Anyway, as we know from adverts, fish and fish oil is a good source of these so that is why there is fish in the ingredients.