﻿MANUAL 
  OF 
  FISH-CULTURE. 
  53 
  

  

  HATCHING. 
  

  

  As 
  the 
  time 
  for 
  hatching 
  draws 
  near, 
  the 
  eggs 
  are 
  placed 
  on 
  trays 
  

   provided 
  with 
  legs 
  or 
  some 
  other 
  support 
  to 
  keep 
  them 
  up 
  from 
  the 
  

   bottom 
  of 
  the 
  trough. 
  Brass 
  nails 
  driven 
  into 
  the 
  under 
  sides 
  of 
  the 
  

   tray 
  rims 
  are 
  good 
  temporary 
  legs, 
  and 
  after 
  the 
  hatching 
  is 
  over 
  they 
  

   are 
  readily 
  removed 
  and 
  the 
  necessity 
  of 
  a 
  special 
  set 
  of 
  trays 
  for 
  

   hatching 
  is 
  avoided. 
  When 
  there 
  are 
  plenty 
  of 
  troughs, 
  these 
  trays 
  

   stand 
  singly 
  on 
  the 
  bottom 
  of 
  the 
  trough, 
  but 
  when 
  it 
  is 
  necessary 
  to 
  

   economize 
  room 
  two 
  or 
  even 
  three 
  are 
  disposed 
  one 
  above 
  another. 
  

   When 
  no 
  necessity 
  exists 
  for 
  economy 
  of 
  space, 
  4,000 
  eggs 
  are 
  allowed 
  

   a 
  whole 
  trough, 
  which 
  is 
  at 
  the 
  rate 
  of 
  400 
  to 
  the 
  square 
  foot; 
  2,000 
  

   or 
  even 
  5,000 
  to 
  the 
  square 
  foot 
  may 
  be 
  carried 
  through 
  hatching 
  and 
  

   the 
  entire 
  sac 
  stage, 
  but 
  the 
  latter 
  number 
  involves 
  risky 
  crowding. 
  

  

  The 
  hatching 
  is 
  sometimes 
  expedited 
  by 
  giving 
  eggs 
  that 
  are 
  just 
  at 
  

   the 
  hatching 
  point 
  a 
  decided 
  shock, 
  similar 
  to 
  that 
  given 
  at 
  an 
  earlier 
  

   date 
  to 
  kill 
  the 
  unimpreguated 
  ones; 
  also 
  by 
  the 
  temporary 
  stoppage 
  

   of 
  the 
  water 
  supply. 
  But 
  at 
  Craig 
  Brook 
  it 
  is 
  the 
  custom 
  to 
  lay 
  the 
  eggs 
  

   out 
  in 
  good 
  season 
  and 
  allow 
  them 
  unlimited 
  time 
  in 
  which 
  to 
  hatch, 
  

   sometimes 
  a 
  week, 
  sometimes 
  two 
  weeks. 
  The 
  earliest 
  lots 
  commonly 
  

   hatch 
  the 
  latter 
  part 
  of 
  March, 
  and 
  it 
  is 
  not 
  often 
  that 
  any 
  remain 
  

   unhatched 
  after 
  April 
  20. 
  The 
  mean 
  duration 
  of 
  the 
  egg 
  stage 
  is 
  

   therefore 
  about 
  157 
  days, 
  during 
  which 
  the 
  mean 
  temperature 
  of 
  the 
  

   water 
  has 
  been 
  about 
  37° 
  F. 
  While 
  hatching 
  is 
  progressing, 
  the 
  outlet 
  

   screens 
  are 
  closely 
  watched 
  to 
  keep 
  the 
  empty 
  shells 
  from 
  clogging 
  

   them 
  up; 
  for 
  when 
  a 
  considerable 
  part 
  of 
  the 
  screen 
  is 
  clogged 
  the 
  

   force 
  of 
  the 
  current 
  through 
  the 
  open 
  spaces 
  is 
  greatly 
  increased, 
  and 
  

   the 
  soft 
  and 
  yielding 
  sacs 
  of 
  the 
  fish 
  are 
  liable 
  to 
  be 
  drawn 
  through 
  

   the 
  meshes. 
  

  

  THE 
  SAC 
  STAGE. 
  

  

  When 
  the 
  shell 
  breaks, 
  though 
  it 
  has 
  been 
  coiled 
  up 
  in 
  a 
  space 
  less 
  

   than 
  ^ 
  inch 
  in 
  diameter, 
  the 
  trunk 
  of 
  the 
  newly 
  hatched 
  salmon 
  at 
  once 
  

   straightens 
  out 
  to 
  a 
  length 
  of 
  about 
  | 
  inch. 
  The 
  yolk, 
  scarcely 
  dimin- 
  

   ished 
  from 
  its 
  original 
  size, 
  hangs 
  beneath 
  and 
  constitutes 
  the 
  greater 
  

   part 
  of 
  the 
  bulk 
  of 
  the 
  fish. 
  The 
  young 
  salmon 
  is 
  for 
  a 
  while 
  more 
  

   Tinwieldly 
  than 
  a 
  tadpole. 
  When 
  frightened 
  he 
  sculls 
  about 
  with 
  great 
  

   energy, 
  but 
  makes 
  slow 
  progress 
  and 
  is 
  fain 
  to 
  lie 
  on 
  his 
  side 
  on 
  the 
  

   bottom 
  of 
  the 
  trough 
  or 
  crowd 
  with 
  his 
  companions 
  into 
  a 
  corner. 
  The 
  

   sac 
  is 
  a 
  store 
  of 
  nutriment, 
  which 
  is 
  gradually 
  absorbed 
  into 
  the 
  other 
  

   parts 
  of 
  the 
  fish 
  ; 
  and 
  so 
  long 
  as 
  it 
  lasts 
  the 
  young 
  salmon 
  will 
  not 
  eat. 
  

   The 
  interval 
  between 
  hatching 
  and 
  total 
  absorption 
  of 
  the 
  sac 
  varies 
  

   with 
  the 
  temperature, 
  the 
  mean 
  at 
  Craig 
  Brook 
  in 
  April 
  and 
  May 
  being 
  

   about 
  six 
  weeks. 
  

  

  As 
  time 
  passes 
  the 
  embryo 
  fish 
  grows 
  more 
  and 
  more 
  to 
  resemble 
  the 
  

   adult, 
  his 
  body 
  acquires 
  strength, 
  and 
  his 
  fins 
  assume 
  form 
  and 
  become 
  

   more 
  effective 
  as 
  organs 
  of 
  propulsion. 
  At 
  last 
  his 
  digestive 
  system 
  

  

  