, ▁sp aw ning , ▁and ▁parent al ▁care . ▁ ▁Be hav iour al ▁sleep ▁ ▁Instead ▁of ▁exam ining ▁brain ▁activity ▁for ▁sleep ▁patterns , ▁an ▁alternate ▁approach ▁is ▁to ▁examine ▁any ▁rest / activity ▁cycles ▁that ▁might ▁indicate ▁" be hav iour al ▁sleep ". ▁The ▁following ▁four ▁behaviour al ▁criteria ▁are ▁characteristic ▁of ▁sleep ▁in ▁birds ▁and ▁m amm als ▁and ▁could ▁be ▁extended ▁to ▁fish es : ▁ ▁( 1 ) ▁prolong ed ▁in activity ; ▁( 2 ) ▁typical ▁rest ing ▁post ure , ▁often ▁in ▁a ▁typical ▁shelter ; ▁( 3 ) ▁altern ation ▁with ▁activity ▁in ▁a ▁ 2 4 - h ▁cycle ; ▁( 4 ) ▁high ▁ar ous al ▁th resh olds . ▁Based ▁on ▁these ▁criteria , ▁many ▁fish ▁species ▁have ▁been ▁observed ▁sleep ing . ▁ ▁The ▁typical ▁sleep ▁post ure ▁of ▁the ▁brown ▁b ull head ▁is ▁with ▁the ▁fins ▁stretch ed ▁out , ▁the ▁tail ▁lying ▁flat ▁on ▁the ▁bottom , ▁the ▁body ▁incl ined ▁to ▁one ▁side ▁at ▁an ▁angle ▁of ▁ 1 0 - 3 0 ▁degrees ▁to ▁the ▁vertical , ▁the ▁card iac ▁and ▁resp ir atory ▁frequencies ▁much ▁slower ▁than ▁normal , ▁and ▁much ▁less ▁sens itivity ▁to ▁sound ▁and ▁to ▁being ▁touched . ▁ ▁Moz amb ique ▁til ap ia ▁are ▁motion less ▁at ▁the ▁bottom ▁at ▁night , ▁with ▁a ▁lower ▁resp ir atory ▁rate ▁and ▁no ▁eye ▁movement , ▁and ▁they ▁do ▁not ▁respond ▁as ▁readily ▁as ▁during ▁the ▁day ▁to ▁elect