﻿MANUAL 
  OF 
  FISH 
  -CULTURE 
  205 
  

  

  bj 
  means 
  of 
  a 
  siphon 
  in 
  the 
  other 
  compartment, 
  running 
  through 
  a 
  hole 
  

   several 
  inches 
  below 
  the 
  top 
  of 
  the 
  trough. 
  The 
  trough 
  fills 
  with 
  water 
  

   up 
  to 
  a 
  level 
  with 
  the 
  hole, 
  when 
  the 
  siphon 
  begins 
  to 
  act 
  and 
  takes 
  off 
  

   the 
  water 
  more 
  rapidly 
  than 
  it 
  enters, 
  to 
  a 
  level 
  with 
  the 
  inner 
  end 
  of 
  

   the 
  siphon, 
  the 
  fall 
  being 
  4 
  to 
  5 
  inches. 
  Air 
  then 
  enters 
  the 
  siphon, 
  

   and 
  it 
  ceases 
  to 
  act 
  until 
  the 
  water 
  has 
  again 
  risen 
  to 
  the 
  height 
  of 
  the 
  

   discharge 
  hole. 
  The 
  water 
  thus 
  rises 
  and 
  falls 
  in 
  thejars 
  automatically, 
  

   the 
  interval 
  between 
  the 
  successive 
  discharges 
  being 
  regulated 
  by 
  the 
  

   length 
  of 
  the 
  inner 
  arm 
  of 
  the 
  siphon, 
  the 
  size 
  of 
  the 
  tube, 
  and 
  amount 
  

   of 
  water 
  supplied. 
  

  

  After 
  the 
  eggs 
  are 
  introduced 
  into 
  thejars 
  a 
  piece 
  of 
  cheese-cloth 
  or 
  

   linen 
  scrim 
  is 
  placed 
  over 
  the 
  top, 
  and 
  fastened 
  by 
  means 
  of 
  rubber 
  

   bands. 
  The 
  jar 
  is 
  then 
  inverted 
  and 
  placed 
  on 
  the 
  wooden 
  supports 
  

   provided 
  for 
  the 
  purpose, 
  and 
  the 
  plug 
  in 
  the 
  bottom 
  removed 
  to 
  allow 
  

   the 
  escape 
  of 
  the 
  air 
  and 
  the 
  rise 
  and 
  fall 
  of 
  water. 
  The 
  number 
  of 
  

   eggs 
  per 
  jar 
  is 
  about 
  190,000 
  or 
  200,000. 
  

  

  DEVELOPMENT 
  OF 
  THE 
  EGG. 
  

  

  The 
  development 
  of 
  the 
  cod 
  egg 
  is 
  greatly 
  influenced 
  by 
  the 
  water 
  

   temperature, 
  which 
  fluctuates 
  from 
  day 
  to 
  day 
  and 
  n)akes 
  it 
  diflicult 
  to 
  

   state 
  exactly 
  when 
  the 
  eggs 
  will 
  hatch. 
  With 
  a 
  high 
  temperature 
  the 
  

   advancement 
  of 
  the 
  egg 
  through 
  the 
  different 
  stages 
  proceeds 
  rapidly 
  

   and 
  can 
  readily 
  be 
  ai)preciated 
  with 
  the 
  unaided 
  eye, 
  while 
  with 
  a 
  low 
  

   temperature 
  the 
  development 
  is 
  slow 
  and 
  may 
  be 
  greatly 
  prolonged 
  

   by 
  very 
  cold 
  water. 
  With 
  a 
  mean 
  temperature 
  of 
  47° 
  cod 
  eggs 
  begin 
  

   to 
  hatch 
  in 
  11 
  days, 
  although 
  2 
  or 
  3 
  additional 
  days 
  are 
  usually 
  nec- 
  

   essary 
  for 
  all 
  the 
  eggs 
  of 
  a 
  given 
  lot 
  to 
  hatch. 
  At 
  43° 
  the 
  time 
  is 
  14 
  

   or 
  15 
  days, 
  and 
  at 
  38° 
  it 
  is 
  20 
  to 
  23 
  days. 
  The 
  best 
  results 
  are 
  obtained 
  

   when 
  the 
  temperature 
  ranges 
  from 
  41° 
  to 
  47°. 
  The 
  hatching 
  proceeds 
  

   satisfactorily 
  with 
  the 
  water 
  at 
  38°, 
  but 
  with 
  a 
  lower 
  temperature 
  

   t^e 
  incubation 
  period 
  is 
  so 
  long 
  that 
  the 
  fry 
  are 
  very 
  weak. 
  On 
  the 
  

   natural 
  spawning-giounds 
  the 
  water 
  seldom 
  gets 
  below 
  38°, 
  while 
  at 
  

   the 
  stations 
  after 
  January 
  1 
  the 
  water 
  used 
  for 
  hatching 
  rarely 
  gets 
  

   as 
  warm 
  as 
  37°, 
  and 
  often 
  is 
  as 
  low 
  as 
  31°; 
  from 
  the 
  middle 
  of 
  January 
  

   to 
  the 
  latter 
  part 
  of 
  February 
  it 
  remains 
  at 
  about 
  32°. 
  Since 
  it 
  is 
  

   impossible 
  to 
  do 
  even 
  fair 
  work 
  when 
  the 
  water 
  gets 
  below 
  35°, 
  it 
  has 
  

   been 
  the 
  practice 
  to 
  warm 
  the 
  water 
  by 
  passing 
  it 
  through 
  a 
  coil 
  of 
  pipe 
  

   contained 
  in 
  a 
  tank 
  of 
  warm 
  water 
  or 
  by 
  introducing 
  steam 
  directly 
  

   into 
  the 
  water 
  pipe 
  whenever 
  the 
  hatchery 
  water 
  gets 
  below 
  37°. 
  

  

  The 
  water 
  being 
  at 
  47°, 
  during 
  the 
  first 
  4 
  days 
  the 
  egg 
  passes 
  

   through 
  the 
  different 
  stages 
  of 
  segmentation; 
  at 
  the 
  end 
  of 
  that 
  time 
  

   the 
  germinal 
  area 
  begins 
  to 
  assume 
  the 
  general 
  form 
  of 
  a 
  fish; 
  and 
  by 
  

   the 
  ninth 
  day 
  the 
  fish 
  is 
  quite 
  well 
  formed, 
  and 
  may 
  be 
  readily 
  seen 
  

   with 
  the 
  naked 
  eye. 
  By 
  the 
  tenth 
  day 
  the 
  embryo 
  shows 
  signs 
  of 
  life, 
  

   and 
  under 
  the 
  microscope 
  the 
  heart 
  may 
  be 
  seen 
  to 
  beat. 
  

  

  