﻿MANUAL 
  OF 
  FISH-CULTUKE. 
  39 
  

  

  dashing 
  down 
  a 
  steep 
  bed 
  has 
  absorbed 
  all 
  the 
  air 
  that 
  is 
  needed 
  in 
  10 
  

   or 
  liO 
  feet 
  of 
  hatching-trough, 
  and 
  demands 
  no 
  further 
  attention 
  on 
  this 
  

   score; 
  but 
  if 
  the 
  water 
  is 
  taken 
  from 
  a 
  lake, 
  a 
  spring, 
  or 
  a 
  quiet 
  brook 
  

   it 
  contains 
  less 
  air, 
  which 
  may 
  be 
  so 
  reduced 
  before 
  it 
  gets 
  through 
  the 
  

   hatching 
  house 
  as 
  to 
  be 
  unable 
  to 
  do 
  its 
  proper 
  work. 
  It 
  is 
  therefore 
  

   desirable 
  to 
  adopt 
  all 
  practicable 
  means 
  of 
  reinforcing 
  it. 
  If 
  the 
  site 
  

   of 
  the 
  hatchnig-house 
  commands 
  a 
  fall 
  of 
  5 
  feet 
  or 
  more, 
  the 
  object 
  

   may 
  be 
  attained 
  bj^ 
  contriving 
  in 
  the 
  conduit 
  outside 
  the 
  house, 
  or 
  in 
  

   the 
  hatching-troughs 
  themselves, 
  a 
  series 
  of 
  miniature 
  cascades. 
  

  

  The 
  broader 
  and 
  thinner 
  the 
  sheet 
  of 
  water 
  the 
  more 
  thoroughly 
  it 
  is 
  

   exposed 
  to 
  the 
  air, 
  and 
  if, 
  instead 
  of 
  being 
  allowed 
  to 
  trickle 
  down 
  the 
  

   face 
  of 
  a 
  perpendicular 
  board, 
  it 
  is 
  carried 
  ofi" 
  so 
  that 
  it 
  must 
  fall 
  free 
  

   through 
  the 
  air, 
  both 
  surfaces 
  of 
  the 
  sheet 
  are 
  exposed 
  and 
  the 
  effect 
  

   doubled. 
  If 
  practicable, 
  it 
  is 
  best 
  to 
  aerate 
  in 
  the 
  conduit, 
  which, 
  as 
  

   already 
  suggested, 
  may 
  be 
  made 
  wide 
  and 
  open 
  for 
  that 
  purpose. 
  

  

  If 
  aeration 
  can 
  not 
  be 
  effected 
  outside 
  the 
  house 
  it 
  may 
  be 
  done 
  

   inside 
  by 
  arranging 
  two 
  long 
  troughs 
  side 
  by 
  side, 
  leveled 
  carefully, 
  

   so 
  that 
  the 
  water 
  is 
  received 
  in 
  one 
  of 
  them 
  and 
  poured 
  over 
  into 
  the 
  

   other 
  in 
  a 
  sheet 
  the 
  whole 
  length 
  of 
  the 
  trough. 
  In 
  the 
  hatching- 
  

   troughs 
  themselves 
  there 
  is 
  an 
  opportunity 
  for 
  aeration 
  either 
  by 
  

   making 
  short 
  troughs 
  with 
  a 
  fall 
  from 
  one 
  to 
  another 
  or 
  by 
  inclining 
  the 
  

   troughs 
  and 
  creating 
  falls 
  at 
  regular 
  distances 
  by 
  partitions 
  or 
  dams, 
  

   each 
  with 
  its 
  cascade, 
  after 
  the 
  fashion 
  already 
  described. 
  The 
  only 
  

   serious 
  difficulty 
  is 
  encountered 
  where 
  the 
  ground 
  is 
  very 
  flat, 
  so 
  that 
  

   the 
  requisite 
  fall 
  can 
  not 
  be 
  obtained, 
  and 
  in 
  this 
  case 
  the 
  best 
  that 
  

   can 
  be 
  done 
  is 
  to 
  make 
  a 
  very 
  large 
  pool, 
  several 
  square 
  rods 
  at 
  least, 
  

   outside 
  the 
  house, 
  and 
  make 
  all 
  the 
  conduits 
  as 
  wide 
  as 
  possible, 
  so 
  

   that 
  the 
  water 
  shall 
  flow 
  in 
  a 
  wide 
  and 
  shallow 
  stream. 
  

  

  It 
  will 
  of 
  course 
  be 
  borne 
  in 
  mind 
  that 
  the 
  better 
  the 
  aeration 
  the 
  

   smaller 
  the 
  volume 
  required 
  to 
  do 
  a 
  given 
  work, 
  and 
  on 
  the 
  other 
  hand 
  

   it 
  is 
  equally 
  true 
  that 
  the 
  greater 
  the 
  volume 
  the 
  less 
  aeration 
  is 
  

   necessary. 
  When 
  so 
  large 
  a 
  volume 
  as 
  6 
  gallons 
  per 
  minute 
  for 
  every 
  

   100,000 
  eggs 
  is 
  at 
  command, 
  a 
  comparatively 
  small 
  amount 
  of 
  aeration 
  

   will 
  answer. 
  But, 
  so 
  far 
  as 
  known, 
  the 
  higher 
  the 
  degree 
  of 
  aeration 
  

   the 
  better 
  the 
  result, 
  without 
  limit, 
  other 
  things 
  being 
  equal, 
  and 
  it 
  is 
  

   therefore 
  advised 
  to 
  make 
  use 
  of 
  all 
  the 
  facilities 
  existing 
  for 
  this 
  

   purpose. 
  

  

  FILTERING. 
  

  

  Before 
  the 
  introduction 
  of 
  wire 
  or 
  glass 
  trays 
  for 
  hatching 
  fish 
  eggs 
  

   it 
  was 
  customary 
  to 
  lay 
  them 
  on 
  gravel, 
  and 
  it 
  was 
  then 
  absolutely 
  

   necessary 
  to 
  filter 
  all 
  but 
  the 
  purest 
  water. 
  Even 
  ordinary 
  spring 
  

   water 
  deposits 
  a 
  very 
  considerable 
  sediment, 
  which 
  might 
  accumulate 
  

   upon 
  the 
  eggs 
  to 
  such 
  an 
  extent 
  as 
  to 
  deprive 
  them 
  of 
  a 
  change 
  of 
  

   water 
  and 
  smother 
  and 
  destroy 
  them. 
  When, 
  however, 
  eggs 
  are 
  depos- 
  

   ited 
  on 
  trays 
  arranged 
  for 
  a 
  circulation 
  of 
  water 
  beneath, 
  as 
  well 
  as 
  over 
  

   them, 
  as 
  described 
  below, 
  even 
  though 
  their 
  upper 
  side.^ 
  are 
  covered 
  

   with 
  sediment, 
  they 
  are 
  clean 
  and 
  bright 
  underneath 
  and 
  remain 
  in 
  

  

  