﻿PROPAGATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  13 
  

  

  The 
  growth 
  of 
  shell, 
  according 
  to 
  my 
  observations, 
  was 
  quite 
  

   rapid 
  for 
  the 
  first 
  few 
  days; 
  at 
  two 
  weeks 
  it 
  was 
  nearly 
  twice 
  as 
  long 
  

   as 
  the 
  glochidium; 
  at 
  four 
  weeks 
  no 
  increase 
  was 
  observed 
  beyond 
  

   that 
  of 
  the 
  second 
  week. 
  This 
  cessation 
  of 
  growth 
  is 
  rather 
  surpris- 
  

   ing, 
  but 
  is 
  in 
  accord 
  with 
  many 
  observations 
  upon 
  growth 
  under 
  

   laboratory 
  conditions. 
  Just 
  what 
  is 
  the 
  cause 
  of 
  this 
  inhibition 
  of 
  

   growth 
  I 
  can 
  only 
  surmise. 
  The 
  young 
  mussels 
  were 
  kept 
  in 
  aquaria 
  

   having 
  a 
  constant 
  stream 
  of 
  running 
  water 
  coming 
  from 
  the 
  river, 
  

   their 
  natural 
  habitat. 
  It 
  is 
  quite 
  likely 
  that 
  under 
  these 
  conditions 
  

   the 
  water 
  contains 
  too 
  small 
  an 
  amount 
  of 
  suitable 
  food 
  material. 
  

   A 
  further 
  discussion 
  of 
  this 
  matter 
  and 
  a 
  more 
  detailed 
  account 
  of 
  

   the 
  early 
  juvenile 
  stages 
  I 
  will 
  reserve 
  for 
  another 
  paper. 
  

  

  The 
  evidence 
  of 
  immunity 
  in 
  Leptops 
  olivaris 
  will 
  be 
  seen 
  by 
  a 
  com- 
  

   parison 
  of 
  results 
  (see 
  table 
  1) 
  in 
  experiments 
  VI-4 
  and 
  VI-20. 
  In 
  

   the 
  latter 
  the 
  glochidia 
  were 
  all 
  shed 
  in 
  less 
  than 
  5 
  days, 
  and 
  thus 
  in 
  

   all 
  probability 
  did 
  not 
  reach 
  maturity. 
  In 
  experiment 
  VI-4 
  the 
  

   small 
  individual 
  carried 
  a 
  large 
  number 
  for 
  11 
  days, 
  the 
  usual 
  period 
  

   of 
  parasitism, 
  while 
  the 
  larger 
  fish 
  on 
  the 
  ninth 
  day 
  had 
  one 
  glochid- 
  

   ium 
  only. 
  

  

  This 
  indication 
  of 
  occasional 
  or 
  even 
  common 
  immunity 
  to 
  these 
  

   glochidia 
  in 
  L. 
  olivaris 
  is 
  suggested 
  in 
  studies 
  of 
  natural 
  infections, 
  

   as 
  I 
  have 
  already 
  shown. 
  The 
  fish 
  is 
  rarely 
  found 
  infected 
  in 
  nature 
  

   by 
  any 
  mussel, 
  and 
  I 
  have 
  only 
  two 
  records 
  of 
  infection 
  by 
  Q. 
  pustu- 
  

   losa. 
  In 
  comparison 
  mth 
  this, 
  the 
  abundant 
  infection 
  of 
  Ictalurus 
  

   pundatus 
  (sometimes 
  as 
  high 
  as 
  50 
  per 
  cent 
  in 
  a 
  catch) 
  forms 
  a 
  

   marked 
  contrast 
  and 
  with 
  the 
  foregoing 
  experiments 
  point 
  conclu- 
  

   sively 
  to 
  the 
  channel 
  cat 
  as 
  the 
  usual 
  host 
  fish 
  and 
  the 
  most 
  suitable 
  

   for 
  artificial 
  propagation. 
  

  

  Tests 
  for 
  optimum 
  infection 
  have 
  been 
  made 
  which 
  indicate 
  that 
  a 
  

   smaller 
  number 
  of 
  glochidia 
  per 
  fish 
  is 
  desirable 
  than 
  in 
  the 
  infections 
  

   with 
  the 
  "mucket" 
  mussel, 
  L. 
  ligamentina. 
  The 
  glochidia 
  in 
  the 
  

   case 
  of 
  Q. 
  pusiulosa 
  are 
  considerably 
  larger 
  and 
  the 
  infection 
  must 
  

   necessarily 
  be 
  made 
  at 
  a 
  season 
  of 
  the 
  year 
  when 
  there 
  is 
  more 
  danger 
  

   of 
  parallel 
  infection 
  with 
  fungus 
  (i. 
  e., 
  Saprolegnia). 
  An 
  infection 
  of 
  

   800 
  to 
  1,000 
  glochidia 
  is 
  recommended 
  for 
  a 
  fish 
  of 
  1 
  pound 
  weight, 
  

   1,500 
  to 
  2,000 
  for 
  a 
  fish 
  of 
  2 
  pounds 
  weight, 
  and 
  proportionate 
  num- 
  

   bers 
  for 
  other 
  sizes. 
  Undoubtedly 
  fish 
  released 
  in 
  their 
  natural 
  

   waters 
  would 
  carry 
  larger 
  infections 
  than 
  those 
  subjected 
  to 
  the 
  more 
  

   severe 
  conditions 
  of 
  experimentation 
  in 
  captivity. 
  In 
  the 
  foregoing 
  

   estimates 
  I 
  have 
  taken 
  account 
  of 
  this. 
  

  

  The 
  collection 
  of 
  gravid 
  mussels 
  of 
  this 
  species 
  for 
  artificial 
  propa- 
  

   gation 
  requires 
  the 
  taldng 
  of 
  some 
  special 
  precautions 
  to 
  prevent 
  the 
  

   premature 
  discharge 
  of 
  the 
  glochidia. 
  The 
  best 
  results 
  are 
  secured, 
  

   in 
  warm 
  weather 
  with 
  mussels 
  that 
  have 
  been 
  collected 
  the 
  same 
  day 
  

   ^nd 
  a 
  short 
  time 
  before 
  the 
  infections 
  are 
  to 
  be 
  made. 
  If 
  the 
  edge 
  

  

  