Like  many  of  the  lower  vertebrate  animals,  especially
fish,  salmon  manifest  intermittent  periods  of  appetite  during
which  growth  proceeds,  and  of  abstinence,  during  which
growth  is  suspended.*  The  salmon  feeds  and  grows  without
intermission  through  the  stages  of  alevin,  parr,  and  smolt,
and  continues  to  do  so  in  the  sea  in  its  transition  to  the
grilse  stage.  Under  the  stimulus  of  unlimited  nutrition,  the
fish  rapidly  increases  in  bulk,  until  the  time  comes  when  its
tissues  are  so  fully  stored  with  fats  and  proteids,  that  no  more
nourishment  can  be  assimilated,  appetite  ceases,  and  the  fish
returns  to  its  native  river.  There  is  no  evidence  to  connect
the  return  of  grilse  in  May,  five  or  six  months  before  the
spawning  season,  with  the  sexual  impulse.  It  appears  probable
that,  the  purpose  with  which  the  fish  visited  the  sea  having
been  accomplished,  it  simply  returns  home,  i.e.,  to  its  native
fresh  water,  which  is  its  most  congenial  environment.  After
an  uncertain  period,  appetite  may  return,  and  the  fish  obeys
the  impulse  to  seek  again  the  salt  water,  teeming  with  various
forms  of  life  offering  an  abundance  which  cannot  be  found
in  the  river.
