﻿MANUAL 
  OF 
  FISH-CULTURE. 
  153 
  

  

  In 
  recoiinectiug, 
  the 
  air 
  may 
  be 
  expelled 
  with 
  the 
  metal 
  top 
  screwed 
  

   down 
  in 
  position. 
  To 
  effect 
  this, 
  draw 
  both 
  glass 
  tubes 
  up 
  to 
  the 
  top 
  of 
  

   the 
  jar 
  and 
  turn 
  on 
  a 
  full 
  head 
  of 
  water, 
  when 
  the 
  air 
  will 
  be 
  forced 
  out 
  

   in 
  bubbles 
  above 
  the 
  eggs, 
  the 
  bubbles 
  escaping 
  through 
  the 
  outlet 
  

   tube. 
  The 
  central 
  tube 
  is 
  now 
  restored 
  to 
  its 
  former 
  position. 
  The 
  

   automatic 
  action 
  permits 
  entire 
  separation 
  of 
  bad 
  from 
  good 
  eggs, 
  

   though 
  some 
  days 
  may 
  be 
  required 
  to 
  accomplish 
  the 
  full 
  result. 
  The 
  

   dead 
  become 
  lighter 
  from 
  gases 
  arising 
  from 
  deconq^osition. 
  A 
  net, 
  

   small 
  enough 
  to 
  easily 
  enter 
  the 
  mouth 
  of 
  the 
  jar 
  and 
  fixed 
  to 
  a 
  handle 
  

   several 
  inches 
  longer 
  than 
  the 
  jar, 
  is 
  convenient 
  for 
  removing 
  particles 
  

   of 
  foreign 
  matter. 
  

  

  Shad 
  eggs 
  are 
  semi-buoyant, 
  and 
  those 
  which 
  will 
  not 
  rise 
  commence 
  

   lumi)ing 
  on 
  the 
  third 
  or 
  fourth 
  day. 
  The 
  usual 
  period 
  of 
  hatching 
  is 
  

   from 
  6 
  to 
  10 
  days, 
  sometimes 
  longer, 
  according 
  to 
  temperature 
  of 
  water, 
  

   but 
  with 
  high 
  temi)erature 
  they 
  will 
  hatch 
  in 
  3 
  days. 
  Fry 
  hatched 
  in 
  

   less 
  than 
  5 
  days 
  are 
  usually, 
  though 
  not 
  always, 
  weak. 
  In 
  general, 
  the 
  

   period 
  of 
  incubation 
  varies 
  inversely 
  with 
  the 
  prevailing 
  temperature, 
  

   but 
  continuous 
  dark 
  and 
  cloudy 
  days 
  will 
  retard 
  and 
  strong 
  light 
  will 
  

   accelerate 
  develoi)ment 
  under 
  preciselj^ 
  the 
  same 
  conditions 
  of 
  water 
  

   temperature, 
  and 
  other 
  circumstances 
  not 
  well 
  understood 
  may 
  also 
  

   have 
  their 
  influence. 
  

  

  Fry 
  when 
  hatched 
  are 
  about 
  0.37 
  inch 
  long. 
  They 
  have 
  been 
  meas- 
  

   ured 
  at 
  intervals 
  of 
  from 
  5 
  to 
  15 
  days, 
  from 
  late 
  in 
  May 
  to 
  the 
  middle 
  

   of 
  October. 
  Toward 
  the 
  middle 
  of 
  August 
  the 
  rate 
  in 
  growth 
  dimin- 
  

   ishes. 
  When 
  9 
  days 
  old 
  they 
  are 
  about 
  0.02 
  inch 
  long. 
  Fry 
  0.5 
  inch 
  

   long 
  July 
  20th 
  were 
  0.75 
  ijich 
  long 
  8 
  days 
  later; 
  on 
  August 
  14th, 
  2 
  to 
  

   2.25 
  inches; 
  September 
  20th, 
  3 
  to 
  4 
  inches; 
  October 
  1st, 
  4 
  to 
  4 
  J 
  inches; 
  

   November 
  4th, 
  5 
  to 
  7 
  inches. 
  Some 
  years 
  they 
  grow 
  faster 
  than 
  others, 
  

   and 
  in 
  some 
  streams 
  more 
  rapidly 
  than 
  in 
  others. 
  From 
  the 
  State 
  fish- 
  

   ponds 
  at 
  Ealeigh, 
  North 
  Carolina, 
  33 
  were 
  removed 
  in 
  November, 
  1884, 
  

   which 
  measured 
  S 
  to 
  9 
  inches. 
  Their 
  usual 
  size 
  in 
  the 
  Potomac 
  in 
  the 
  

   fall 
  is 
  3 
  to 
  4 
  inches. 
  

  

  MEASURING 
  THE 
  EGGS 
  AND 
  FRY. 
  

  

  To 
  estimate 
  the 
  number 
  of 
  eggs 
  and 
  of 
  the 
  young 
  fry 
  was 
  for 
  years 
  

   rather 
  a 
  difficult 
  matter 
  to 
  accomplish 
  satisfactorily. 
  The 
  standard 
  

   made 
  use 
  of 
  at 
  the 
  outset 
  was 
  undoubtedly 
  much 
  too 
  high. 
  The 
  scale 
  

   most 
  used 
  at 
  present 
  is 
  a 
  light 
  square, 
  made 
  of 
  wood, 
  the 
  longer 
  leg 
  

   being 
  15 
  inches 
  and 
  the 
  shorter 
  7^ 
  inches 
  long. 
  The 
  material 
  is 
  ^ 
  inch 
  

   wide 
  and 
  ^ 
  inch 
  thick. 
  The 
  graduations 
  are 
  on 
  the 
  longer 
  leg, 
  and 
  

   read 
  from 
  the 
  lower 
  end 
  upward. 
  The 
  first 
  line 
  is 
  at 
  a 
  height 
  corre- 
  

   sponding 
  to 
  the 
  level 
  attained 
  in 
  the 
  jar 
  by 
  a 
  measured 
  half-pint 
  of 
  

   water, 
  and 
  the 
  succeeding 
  lines 
  are 
  determined 
  by 
  the 
  introduction 
  of 
  

   additional 
  half-pints 
  of 
  water. 
  When 
  the 
  scale 
  is 
  being 
  constructed, 
  

   the 
  central 
  glass 
  tube 
  is 
  stopped 
  at 
  the 
  lower 
  end 
  that 
  it 
  maj'' 
  displace 
  

   an 
  amonu't 
  of 
  water 
  equal 
  to 
  the 
  amount 
  of 
  eggs 
  it 
  will 
  displace 
  in 
  

  

  