﻿MANUAL 
  OF 
  FISH-CULTURE. 
  .145 
  

  

  should 
  be 
  discolored 
  enough 
  to 
  preveut 
  the 
  fish 
  from 
  seeing 
  the 
  nets, 
  

   but 
  not 
  thick, 
  say 
  from 
  10 
  to 
  20.* 
  An 
  occasional 
  freshet 
  reduces 
  the 
  

   temperature 
  and 
  prolongs 
  the 
  season 
  ; 
  however, 
  with 
  an 
  equal 
  number 
  

   of 
  fish 
  in 
  the 
  rivers, 
  clear 
  water 
  is 
  probably 
  more 
  advantageous 
  for 
  

   natural 
  increase, 
  as 
  a 
  large 
  i)roportion 
  of 
  naturally 
  deposited 
  eggs 
  must 
  

   perish 
  from 
  sufibcation 
  under 
  the 
  mud 
  in 
  seasons 
  of 
  freshet. 
  

  

  THE 
  WEATHER 
  AND 
  SPAWN. 
  

  

  The 
  development 
  of 
  eggs 
  within 
  the 
  ovaries 
  is 
  hastened 
  by 
  heat 
  and 
  

   retarded 
  by 
  cold. 
  In 
  a 
  warm 
  season 
  fish 
  ready 
  to 
  spawn 
  are 
  more 
  

   numerous 
  early 
  in 
  the 
  season 
  than 
  in 
  a 
  cold 
  one, 
  and 
  the 
  period 
  for 
  

   obtaining 
  them 
  is 
  apt 
  to 
  close 
  earlier. 
  The 
  eggs, 
  not 
  only 
  after 
  they 
  

   are 
  deposited 
  and 
  impregnated, 
  but 
  before 
  they 
  leave 
  the 
  body 
  of 
  the 
  fish, 
  

   are 
  affected 
  by 
  the 
  temperature 
  of 
  the 
  water, 
  often 
  being 
  "blighted" 
  

   or 
  "rotten 
  ripe." 
  This 
  phenomenon 
  was 
  observed 
  as 
  far 
  back 
  as 
  1873. 
  

   It 
  occurs 
  on 
  the 
  water 
  reaching 
  80° 
  to 
  81°, 
  or 
  with 
  a 
  rapid 
  rise. 
  On 
  

   the 
  other 
  hand, 
  a 
  sudden 
  fall 
  in 
  temperature 
  has 
  been 
  observed 
  to 
  

   arrest 
  natural 
  spawning, 
  produce 
  blighted 
  eggs, 
  and 
  to 
  destroy 
  those 
  

   in 
  the 
  hatching-vessels. 
  Continued 
  low 
  temperature 
  is 
  also 
  disastrous 
  

   to 
  fishing. 
  

  

  An 
  abnormally 
  inferior 
  quality 
  of 
  the 
  Potomac 
  Eiver 
  eggs 
  was 
  noticed 
  

   during 
  the 
  full 
  period 
  of 
  operations 
  in 
  189G. 
  The 
  bulk 
  of 
  the 
  run 
  of 
  shad 
  

   made 
  their 
  appearance 
  on 
  a 
  rapidly 
  ascending 
  temperature, 
  and 
  the 
  

   eggs 
  were 
  injured 
  within 
  the 
  parent 
  fish, 
  more 
  than 
  half 
  perishing 
  

   before 
  conversion 
  into 
  fry. 
  The 
  rise 
  in 
  temperature 
  was 
  greater 
  than 
  

   had 
  been 
  recorded 
  in 
  the 
  eleven 
  years 
  preceding. 
  The 
  run 
  of 
  shad 
  

   increased 
  proportionately, 
  the 
  catch 
  at 
  one 
  seine 
  increasing 
  from 
  100 
  

   to 
  800 
  in 
  24: 
  hours. 
  A 
  snowstorm 
  on 
  April 
  7— 
  morning 
  air 
  temperature 
  

   35° 
  F. 
  and 
  mean 
  air 
  temperature 
  40° 
  — 
  was 
  followed 
  by 
  heavy 
  frost 
  on 
  

   April 
  9, 
  the 
  morning 
  air 
  temperature 
  on 
  the 
  last-named 
  date 
  being 
  34°. 
  

   The 
  river 
  water 
  on 
  April 
  10 
  was 
  4G°, 
  rising 
  to 
  48° 
  on 
  April 
  12 
  and 
  to 
  

   71° 
  in 
  the 
  afternoon 
  of 
  April 
  21, 
  thus 
  gaining 
  25° 
  in 
  10 
  days. 
  After 
  

   April 
  21 
  the 
  catch 
  of 
  shad 
  fell 
  off 
  to 
  such 
  an 
  extent 
  that 
  fishing 
  was 
  

   no 
  longer 
  profitable. 
  

  

  The 
  water 
  of 
  the 
  Potomac 
  early 
  in 
  March 
  is 
  usually 
  of 
  a 
  temjierature 
  

   of 
  36° 
  to 
  40°, 
  rising 
  to 
  52° 
  to 
  5S° 
  about 
  the 
  middle 
  of 
  April, 
  when 
  the 
  

   spawning 
  period 
  begins, 
  and 
  at 
  the 
  end 
  of 
  May, 
  the 
  close 
  of 
  the 
  period, 
  

   it 
  averages 
  from 
  ■65° 
  to 
  70°. 
  

  

  STRIPPING 
  AND 
  FERTILIZING 
  THE 
  EGGS. 
  

  

  In 
  stripping 
  the 
  eggs 
  the 
  shad 
  is 
  lifted 
  with 
  the 
  right 
  hand 
  and 
  

   caught 
  above 
  the 
  tail 
  with 
  the 
  left. 
  All 
  slime 
  and 
  loose 
  scales 
  are 
  

   removed 
  by 
  going 
  over 
  the 
  fish 
  two 
  or 
  three 
  times 
  in 
  quick 
  succession 
  

   with 
  the 
  right 
  hand. 
  The 
  head 
  is 
  carried 
  to 
  the 
  left 
  side 
  under 
  the 
  

  

  *The 
  condition 
  that 
  permits 
  the 
  discernment 
  of 
  objects 
  at 
  a 
  distance 
  of 
  10 
  to 
  20 
  

   inches 
  beneath 
  the 
  water 
  surface, 
  the 
  method 
  of 
  registration 
  employed 
  by 
  the 
  Wash- 
  

   ington 
  CD, 
  C.) 
  aciueduct 
  office. 
  

  

  F. 
  C. 
  K, 
  1897 
  10 
  

  

  