﻿6 
  GROWTH 
  AND 
  MfGRATION 
  OF 
  FRESH- 
  WATER 
  MUSSELS, 
  

  

  the 
  age 
  question. 
  After 
  carrying 
  on 
  experimental 
  work 
  for 
  some 
  time 
  

   on 
  my 
  own 
  initiative, 
  I 
  was 
  given 
  opportunity 
  in 
  1910 
  to 
  undertake 
  

   the 
  work 
  on 
  a 
  larger 
  scale 
  under 
  the 
  direction 
  of 
  the 
  Commissioner 
  of 
  

   Fisheries. 
  

  

  PLAN 
  OF 
  INVESTIGATION. 
  

  

  In 
  the 
  experiments 
  to 
  ho 
  undertaken 
  I 
  proposed 
  to 
  ascertain 
  the 
  

   rate 
  of 
  growth, 
  to 
  mquire 
  mto 
  the 
  meaning 
  of 
  growth 
  lines, 
  to 
  hwes- 
  

   tigate 
  the 
  relation 
  of 
  age, 
  maximum 
  size, 
  etc., 
  and, 
  as 
  a 
  secondary 
  

   problem, 
  to 
  gather 
  data 
  concerning 
  migration. 
  The 
  plan 
  of 
  work 
  

   was, 
  in 
  brief, 
  to 
  collect 
  a 
  thousand 
  specimens 
  of 
  as 
  many 
  species 
  and 
  

   sizes 
  as 
  could 
  be 
  secured 
  in 
  the 
  region 
  where 
  the 
  work 
  was 
  carried 
  on 
  ; 
  

   in 
  some 
  way 
  mark 
  them 
  individually, 
  weigh, 
  measure, 
  and 
  make 
  any 
  

   other 
  necessary 
  records; 
  and 
  then 
  return 
  them 
  to 
  their 
  usual 
  habitat 
  

   and 
  at 
  suitable 
  intervals 
  reclaim, 
  weigh, 
  and 
  measure 
  again. 
  

  

  To 
  carry 
  out 
  this 
  work, 
  two 
  questions 
  of 
  method 
  had 
  to 
  be 
  solved 
  : 
  

   (1) 
  The 
  marking 
  of 
  specimens 
  and 
  (2) 
  the 
  reclaiming 
  of 
  them. 
  

  

  MARKING 
  OF 
  SPECIMENS. 
  

  

  In 
  1909 
  I 
  experimented- 
  with 
  two 
  ways 
  of 
  marking: 
  One 
  was 
  to 
  

   scratch 
  a 
  symbol 
  (pi. 
  i, 
  H), 
  as 
  a 
  Roman 
  numeral, 
  on 
  the 
  shell, 
  and 
  

   in 
  this 
  way 
  identify 
  it 
  for 
  future 
  records; 
  the 
  second 
  method 
  was 
  to 
  

   fasten 
  a 
  serial-numbered 
  tag 
  to 
  the 
  shell 
  and 
  keep 
  records 
  by 
  these 
  

   numbers. 
  In 
  the 
  final 
  work 
  both 
  methods 
  were 
  used, 
  the 
  former 
  for 
  

   hght 
  shells, 
  the 
  latter 
  for 
  heavy 
  ones. 
  

  

  The 
  method 
  of 
  marking 
  a 
  shell 
  by 
  scratching 
  a 
  number 
  on 
  it 
  is 
  

   simple 
  enough, 
  as 
  a 
  mark 
  cut 
  through 
  the 
  epidermis 
  of 
  a 
  mussel 
  

   valve 
  will 
  be 
  carried 
  indefinitely. 
  To 
  get 
  a 
  satisfactory 
  series 
  for 
  

   a 
  large 
  number 
  of 
  specimens, 
  however, 
  is 
  difficult. 
  

  

  The 
  tagging 
  with 
  serial 
  numbers 
  seemed 
  to 
  me 
  to 
  be 
  more 
  exact. 
  

   For 
  this 
  method 
  I 
  used 
  brass 
  tags 
  about 
  the 
  size 
  of 
  a 
  dime 
  and 
  

   fastened 
  them 
  to 
  the 
  specimens 
  with 
  a 
  hght 
  copper 
  \vire 
  passed 
  

   through 
  a 
  small 
  hole 
  made 
  in 
  the 
  posterior 
  edge 
  of 
  the 
  valve. 
  The 
  

   hole 
  in 
  the 
  valve 
  was 
  made 
  with 
  a 
  very 
  fine 
  button-eye 
  drill 
  about 
  

   2 
  milhmeters 
  from 
  the 
  posterior 
  edge 
  of 
  the 
  shell 
  (pi. 
  i, 
  ii, 
  and 
  iii). 
  

   To 
  hold 
  the 
  button-eye 
  drill, 
  a 
  geared 
  hand 
  driU 
  was 
  used, 
  and 
  only 
  a 
  

   few 
  seconds 
  were 
  needed 
  to 
  drill 
  a 
  hole 
  even 
  in 
  a 
  thick 
  shell. 
  By 
  

   makmg 
  a 
  little 
  hook 
  on 
  the 
  wire 
  it 
  could 
  be 
  passed 
  through 
  the 
  hole 
  

   and 
  out 
  between 
  the 
  valves, 
  usually 
  without 
  much 
  difficulty. 
  In 
  

   large 
  specimens 
  it 
  was 
  found 
  that 
  the 
  work 
  of 
  tagging 
  could 
  be 
  more 
  

   readily 
  accomplished 
  by 
  wedging 
  the 
  valves 
  open 
  slightly 
  before 
  

   inserting 
  the 
  wdre. 
  A 
  slight 
  injury 
  to 
  the 
  animal 
  often 
  resulted 
  

   from 
  the 
  fact 
  that 
  the 
  mantle 
  was 
  not 
  sufficiently 
  drawn 
  back 
  to 
  

   avoid 
  the 
  drill 
  point. 
  T\Tiile 
  the 
  irritation 
  at 
  the 
  moment 
  was 
  

  

  