▁species ▁( the ▁green ▁chrom is , ▁the ▁margin ate ▁das cy ll us ▁and ▁the ▁wh itet ail ▁das cy ll us ) ▁spend ▁the ▁night ▁between ▁cor al ▁branches ▁where ▁they ▁beat ▁their ▁fins ▁at ▁a ▁rate ▁about ▁twice ▁that ▁of ▁normal ▁day time ▁sw imming . ▁This ▁creates ▁water ▁curr ents ▁that ▁keep ▁the ▁inner ▁zone ▁of ▁the ▁cor al ▁( and ▁thus ▁the ▁fish ▁themselves ) ▁well ▁o xygen ated , ▁at ▁levels ▁about ▁four ▁times ▁higher ▁than ▁in ▁the ▁absence ▁of ▁the ▁fish . ▁Though ▁the ▁fish ▁are ▁active ▁( most ly ▁in ▁a ▁repet itive ▁way ), ▁they ▁do ▁not ▁respond ▁to ▁light ▁or ▁to ▁the ▁presence ▁of ▁potential ▁pred ators . ▁The ▁research ers ▁who ▁documented ▁this ▁behaviour ▁called ▁it ▁" sleep - sw imming ". ▁ ▁S leep ▁could ▁also ▁be ▁absent ▁during ▁specific ▁parts ▁of ▁a ▁fish ' s ▁life . ▁Species ▁normally ▁qu ies cent ▁at ▁night ▁become ▁active ▁day ▁and ▁night ▁during ▁the ▁sp aw ning ▁season . ▁ ▁Many ▁parent al ▁species ▁for ego ▁sleep ▁at ▁night ▁and ▁fan ▁their ▁eggs ▁day ▁and ▁night ▁for ▁many ▁days ▁in ▁a ▁row . ▁This ▁has ▁been ▁observed ▁in ▁thre esp ine ▁stick le back , ▁ ▁conv ict ▁c ich l id ▁and ▁rain bow ▁c ich l id , ▁ ▁various ▁species ▁of ▁dam self ish , ▁ ▁small mouth ▁bass ▁and ▁larg em outh ▁bass , ▁and ▁the ▁brown ▁b ull head . ▁Some ▁di urn al ▁species , ▁like ▁the