▁fin ▁is ▁small ▁and ▁has ▁ 4 - 5 ▁weak ▁sp ines , ▁while ▁the ▁posterior ▁fin ▁is ▁larger , ▁with ▁one ▁sp ine ▁and ▁ 8 ▁or ▁ 9 ▁ray s . ▁The ▁length y ▁anal ▁fin ▁is ▁somewhat ▁sick le - sh aped , ▁has ▁one ▁sp ine ▁and ▁ 1 6 ▁to ▁ 1 8 ▁ray s . ▁As ▁bef its ▁the ▁name , ▁they ▁are ▁sil very ▁on ▁the ▁sides ; ▁the ▁back ▁is ▁somewhat ▁yellow ish , ▁and ▁the ▁unders ide ▁is ▁a ▁transl uc ent ▁green ish . ▁These ▁are ▁small ▁fish , ▁with ▁ 1 5   cm ▁recorded , ▁but ▁most ▁adult s ▁ 1 0   cm ▁or ▁less . ▁ ▁They ▁primarily ▁feed ▁on ▁zo op l ank ton , ▁moving ▁in ▁enorm ous ▁schools ▁capable ▁of ▁de ple ting ▁populations ▁of ▁the ▁small ▁ar th rop ods ▁and ▁cr ust ace ans ▁they ▁favor . ▁In ▁turn , ▁they ▁are ▁pre y ▁for ▁a ▁variety ▁of ▁fish ▁and ▁birds . ▁The ▁sil vers ides ▁con greg ate ▁in ▁the ▁shall ows , ▁generally ▁over ▁sand ▁or ▁gra vel ▁bottom s ▁with ▁overhead ▁cover ▁if ▁possible , ▁but ▁then ▁move ▁out ▁to ▁open ▁water ▁in ▁search ▁of ▁additional ▁food , ▁which ▁increases ▁pred ation ▁risk . ▁They ▁are ▁often ▁observed ▁in ▁a ▁sort ▁of ▁daily ▁migration ▁pattern ▁as ▁a ▁result . ▁ ▁The ▁exact ▁native ▁range ▁of ▁the ▁in land ▁sil vers ide ▁is ▁not ▁known ; ▁they ▁are ▁w ides p read