﻿MANUAL 
  OF 
  FISH-CULTURE. 
  213 
  

  

  eggs. 
  The 
  largest 
  number 
  of 
  eggs 
  takeu 
  from 
  one 
  fish 
  in 
  Casco 
  Bay 
  

   in 
  1897 
  was 
  200,000. 
  

  

  From 
  the 
  field 
  the 
  fertilized 
  eggs 
  are 
  conveyed 
  to 
  the 
  station 
  in 
  jars, 
  

   as 
  described 
  in 
  the 
  chapter 
  on 
  cod 
  propagation. 
  For 
  short 
  shipments 
  

   they 
  may 
  be 
  transported 
  in 
  buckets 
  or 
  cans. 
  

  

  Mackerel 
  eggs 
  may 
  be 
  artificially 
  incubated 
  in 
  a 
  variety 
  of 
  ways. 
  In 
  

   1896 
  three 
  forms 
  of 
  apparatus 
  were 
  employed 
  for 
  comparative 
  purposes. 
  

   These 
  were 
  (1) 
  the 
  McDonald 
  hatching-jar, 
  with 
  the 
  water 
  supplied 
  

   through 
  the 
  long 
  central 
  tube 
  and 
  discharged 
  through 
  a 
  cheesecloth 
  

   top; 
  (2) 
  the 
  Chester 
  jar, 
  and 
  (.3) 
  the 
  automatic 
  tidal-box; 
  the 
  latter 
  

   gave 
  the 
  best 
  results. 
  

  

  Owing 
  to 
  the 
  very 
  small 
  size 
  of 
  the 
  eggs, 
  from 
  200,000 
  to 
  225,000 
  

   may 
  be 
  placed 
  in 
  a 
  Chester 
  jar 
  and 
  450,000 
  or 
  more 
  in 
  a 
  tidal 
  box 
  20 
  

   by 
  11 
  inches. 
  The 
  eggs 
  are 
  manipulated 
  in 
  about 
  the 
  same 
  way 
  that 
  

   cod 
  eggs 
  are, 
  but, 
  owing 
  to 
  the 
  short 
  period 
  of 
  incubation, 
  require 
  very 
  

   little 
  handling. 
  

  

  For 
  reasons 
  not 
  yet 
  definitely 
  determined, 
  but 
  apparently 
  connected 
  

   with 
  the 
  condition 
  of 
  the 
  eggs 
  rather 
  than 
  the 
  methods 
  of 
  hatching, 
  

   mackerel 
  ova 
  are 
  liable 
  to 
  exceedingly 
  large 
  mortality 
  during 
  incuba- 
  

   tion. 
  While 
  as 
  many 
  as 
  75 
  per 
  cent 
  of 
  certain 
  small 
  lots 
  of 
  eggs 
  have 
  

   produced 
  fry, 
  less 
  than 
  1 
  per 
  cent 
  of 
  most 
  of 
  the 
  eggs 
  hatch. 
  

  

  The 
  period 
  of 
  incubation 
  at 
  a 
  mean 
  water-temperature 
  of 
  58° 
  is 
  about 
  

   5 
  days. 
  In 
  48 
  hoilrs 
  after 
  impregnation 
  the 
  embryo 
  is 
  discernible, 
  and 
  

   in 
  08 
  hours 
  its 
  development 
  is 
  far 
  advanced. 
  The 
  critical 
  period 
  seems 
  

   to 
  be 
  the 
  end 
  of 
  the 
  third 
  day, 
  when 
  a 
  large 
  part 
  of 
  the 
  eggs 
  die. 
  

  

  The 
  fry 
  are 
  planted 
  withiu 
  24 
  hours 
  of 
  hatching. 
  They 
  are 
  taken 
  

   to 
  the 
  natural 
  spawning-grounds 
  in 
  regular 
  transportation 
  cans 
  and 
  

   liberated 
  below 
  the 
  surface 
  of 
  the 
  water. 
  

  

  