﻿MANUAL 
  OF 
  FISH-CULTURE. 
  65 
  

  

  The 
  couditioiis 
  at 
  Craig 
  Pond, 
  M^here 
  some 
  of 
  the 
  worst 
  cases 
  recov- 
  

   ered, 
  were 
  these: 
  Au 
  area 
  of 
  231 
  acres; 
  a 
  maximum 
  depth 
  of 
  09 
  feet; 
  

   exceedingly 
  pure 
  and 
  transparent 
  water, 
  like 
  that 
  of 
  the 
  iuclosure. 
  

  

  At 
  two 
  of 
  the 
  other 
  iuclosures 
  tried 
  that 
  summer, 
  where 
  there 
  was 
  

   no 
  attack 
  of 
  fungus, 
  the 
  water 
  was 
  brown 
  and 
  dark, 
  like 
  that 
  of 
  ordi- 
  

   nary 
  brooks 
  and 
  jionds, 
  and 
  in 
  the 
  remaining 
  one 
  it 
  was 
  intermediate 
  

   in 
  character. 
  

  

  These 
  facts 
  point 
  strongly 
  to 
  the 
  character 
  of 
  the 
  water 
  as 
  the 
  cause 
  

   of 
  the 
  fatality 
  of 
  the 
  disease, 
  and 
  especially 
  to 
  its 
  pellucid 
  character, 
  

   which 
  exi)osed 
  the 
  salmon 
  to 
  an 
  extraordinary 
  glare 
  of 
  light, 
  whereby 
  

   the 
  growth 
  of 
  the 
  pest 
  was 
  greatly 
  encouraged. 
  The 
  recovery 
  in 
  the 
  

   transparent 
  water 
  of 
  Craig 
  Pond 
  was 
  rendered 
  possible 
  by 
  the 
  great 
  

   depth 
  of 
  the 
  water, 
  through 
  which 
  but 
  a 
  small 
  fraction 
  of 
  the 
  light 
  of 
  

   day 
  could 
  penetrate. 
  No 
  doubt 
  the 
  salmon 
  liberated 
  there 
  at 
  once 
  took 
  

   refuge 
  in 
  the 
  deeper 
  parts. 
  The 
  suggestion 
  naturallj' 
  arises 
  that 
  arti- 
  

   ficial 
  shade 
  might 
  be 
  useful 
  in 
  the 
  treatment 
  of 
  such 
  diseases, 
  whether 
  

   the 
  attacking 
  fungus 
  be 
  identical 
  with 
  that 
  observed 
  in 
  the 
  above 
  in- 
  

   stances 
  or 
  a 
  related 
  one. 
  

  

  It 
  is 
  certain, 
  from 
  the 
  promptness 
  with 
  which 
  dead 
  animal 
  matter 
  

   becomes 
  the 
  prey 
  of 
  saprophytic 
  growths, 
  that 
  the 
  spores 
  of 
  these 
  

   water-molds 
  are 
  well 
  disseminated 
  throughout 
  fresh 
  waters, 
  everywhere 
  

   ready 
  to 
  seize 
  upon 
  an 
  opportunity 
  for 
  germination 
  and 
  growth, 
  and 
  

   that 
  as 
  a 
  general 
  rule 
  these 
  spores 
  are 
  quite 
  unable 
  to 
  seize 
  upon 
  any 
  

   animal 
  substance 
  which 
  is 
  not 
  already 
  dead 
  or 
  in 
  a 
  diseased 
  condition, 
  

  

  A 
  growth 
  of 
  Saprolegnia 
  ferax 
  once 
  established 
  on 
  the 
  body 
  of 
  a 
  

   salmon 
  is 
  able 
  to 
  extend 
  itself 
  upou 
  and 
  into 
  the 
  living 
  tissues 
  around 
  

   it, 
  which 
  it 
  seizes 
  upon 
  and 
  destroys. 
  Growing 
  upon 
  u 
  dead 
  egg, 
  it 
  not 
  

   only 
  ensnares 
  the 
  neighboring 
  living 
  eggs, 
  but 
  sometimes 
  pierces 
  their 
  

   shells 
  and 
  establishes 
  itself 
  on 
  the 
  internal 
  parts. 
  In 
  one 
  instance 
  the 
  

   fungus 
  had 
  gone 
  so 
  far 
  as 
  to 
  attach 
  itself 
  to 
  a 
  living 
  embryo, 
  which, 
  on 
  

   removal 
  from 
  the 
  shell, 
  was 
  found 
  to 
  support 
  on 
  the 
  sac 
  quite 
  a 
  tut't 
  of 
  

   growing 
  fungus, 
  though 
  neither 
  on 
  the 
  sac 
  nor 
  any 
  other 
  part 
  of 
  the 
  

   fish 
  was 
  a 
  trace 
  of 
  dead 
  substance 
  discernible. 
  

  

  It 
  has 
  been 
  asce<rtained 
  that 
  the 
  Scvprolegnia 
  which 
  attacked 
  the 
  

   living 
  salmon 
  can 
  be 
  communicated 
  by 
  contact 
  to 
  dead 
  flies, 
  and 
  that 
  

   Saprolegnia 
  found 
  growing 
  in 
  the 
  ordinary 
  way 
  on 
  dead 
  flies 
  in 
  water 
  

   can 
  be 
  communicated 
  in 
  its 
  turn 
  to 
  living 
  and 
  healthy 
  dace 
  and 
  may 
  

   so 
  flourish 
  on 
  them 
  as 
  to 
  cause 
  their 
  death. 
  

  

  The 
  impression 
  has 
  i)revailed 
  that 
  the 
  Saprolegnia 
  which 
  infests 
  the 
  

   eggs 
  in 
  hatching-troughs 
  originates 
  in 
  or 
  is 
  encouraged 
  by 
  bare 
  wood 
  

   exposed 
  to 
  water, 
  and 
  that 
  special 
  effort 
  is 
  necessary 
  to 
  prevent 
  its 
  

   forming; 
  but 
  experience 
  at 
  this 
  station 
  does 
  not 
  show 
  that 
  attacks 
  of 
  

   fungus 
  on 
  either 
  eggs 
  or 
  fish 
  could 
  be 
  traced 
  to 
  bare 
  wood, 
  and, 
  on 
  the 
  

   other 
  hand, 
  eggs 
  and 
  fish 
  in 
  troughs 
  carefully 
  varnished 
  with 
  asphaltum 
  

   are 
  no 
  freer 
  from 
  fungoid 
  or 
  other 
  disease 
  than 
  those 
  in 
  neighboring 
  

   troughsfrom 
  which 
  long 
  use 
  had 
  worn 
  almost 
  the 
  last 
  vestige 
  of 
  varnish. 
  

  

  F. 
  C. 
  R. 
  1897 
  5 
  

  

  