﻿REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  93 
  

  

  pected 
  until 
  a 
  special 
  examination 
  of 
  the 
  water 
  supply 
  disclosed 
  great 
  

   numbers 
  of 
  a 
  minute 
  animal 
  in 
  the 
  hatching 
  troughs. 
  Mr. 
  A. 
  E. 
  Beards- 
  

   ley, 
  professor 
  of 
  biology 
  in 
  the 
  State 
  Normal 
  School 
  at 
  Greeley, 
  Colo., 
  

   was 
  asked 
  to 
  visit 
  the 
  hatchery 
  and 
  look 
  into 
  the 
  mortality 
  among 
  the 
  

   fish; 
  and 
  his 
  report 
  '^ 
  shows 
  conclusively 
  that 
  the 
  trouble 
  was 
  due 
  to 
  a 
  

   species 
  of 
  hydra, 
  which 
  gained 
  access 
  to 
  the 
  hatchery 
  from 
  a 
  shallow 
  

   lake 
  which 
  is 
  one 
  of 
  the 
  sources 
  of 
  water 
  supply. 
  A 
  careful 
  investi- 
  

   gation 
  having 
  failed 
  to 
  disclose 
  any 
  other 
  cause 
  for 
  the 
  death 
  of 
  trout, 
  

   and 
  the 
  hydras 
  being 
  known 
  to 
  be 
  armed 
  with 
  dart 
  cells, 
  which 
  secrete 
  

   a 
  fluid 
  by 
  which 
  small 
  crustaceans 
  and 
  other 
  animals 
  are 
  quickly 
  para- 
  

   lyzed, 
  the 
  responsibility 
  of 
  the 
  hydras 
  was 
  demonstrated 
  by 
  experi- 
  

   mental 
  tests. 
  Newly-hatched 
  fry 
  were 
  placed 
  in 
  beakers 
  filled 
  with 
  

   water 
  from 
  the 
  supply 
  pipes 
  with 
  a 
  little 
  sediment 
  from 
  the 
  hatching 
  

   trough 
  in 
  which 
  the 
  hydras 
  were 
  found. 
  In 
  less 
  than 
  thirty 
  minutes 
  

   25 
  per 
  cent 
  of 
  the 
  fry 
  were 
  dead, 
  and 
  in 
  seventy-five 
  minutes 
  all 
  were 
  

   dead, 
  while 
  in 
  a 
  beaker 
  filled 
  with 
  water 
  containing 
  no 
  hydras 
  all 
  the 
  

   fry 
  were 
  alive 
  the 
  next 
  day. 
  With 
  the 
  aid 
  of 
  a 
  lens 
  the 
  hydras 
  could 
  

   be 
  seen 
  with 
  their 
  mouths 
  closely 
  applied 
  to 
  the 
  surface 
  of 
  the 
  fry, 
  

   particularly 
  on 
  the 
  yolk 
  sac 
  — 
  a 
  dozen 
  hydras 
  sometimes 
  attaching 
  them- 
  

   selves 
  to 
  a 
  single 
  fish. 
  When 
  first 
  attacked 
  the 
  fish 
  struggled 
  violently, 
  

   but 
  the 
  movements 
  gradually 
  diminished 
  in 
  frequency 
  and 
  intensity 
  

   until 
  death 
  supervened. 
  

  

  This 
  hatchery 
  pest 
  is 
  to 
  be 
  overcome 
  by 
  excluding 
  water 
  from 
  the 
  

   lake 
  containing 
  hydra, 
  and 
  by 
  scrubbing 
  the 
  troughs 
  with 
  a 
  stiff 
  brush 
  

   and 
  then 
  quickl}^ 
  flushing 
  them 
  so 
  as 
  to 
  wash 
  out 
  the 
  hydras 
  before 
  

   they 
  can 
  become 
  attached. 
  

  

  This 
  particular 
  hydra 
  appears 
  to 
  represent 
  an 
  undescribed 
  form, 
  

   characterized 
  by 
  its 
  large 
  size 
  and 
  absence 
  of 
  color, 
  and 
  has 
  been 
  

   named 
  Hydra 
  pallida 
  by 
  Mr. 
  Beardsley. 
  

  

  GAS 
  DISEASE 
  IN 
  AQUARIUM 
  FISH. 
  

  

  For 
  a 
  number 
  of 
  years 
  the 
  aquarium 
  at 
  the 
  Woods 
  Hole 
  station 
  has 
  

   with 
  great 
  difficulty 
  been 
  kept 
  stocked 
  with 
  fish 
  and 
  other 
  animals, 
  

   owing 
  to 
  their 
  rapid 
  death 
  from 
  what 
  has 
  come 
  to 
  be 
  known 
  as 
  the 
  gas 
  

   or 
  bubble 
  disease. 
  The 
  condition 
  of 
  affairs 
  having 
  become 
  more 
  aggra- 
  

   vated, 
  it 
  Avas 
  necessaiy, 
  in 
  the 
  interest 
  of 
  the 
  fish-cultural 
  work, 
  as 
  

   well 
  as 
  of 
  the 
  biological 
  laboratory, 
  to 
  give 
  the 
  matter 
  special 
  atten- 
  

   tion. 
  In 
  the 
  Bulletin 
  for 
  1899 
  Prof. 
  F. 
  P. 
  Gorham 
  published 
  a 
  paper^ 
  

   which 
  explained 
  some 
  of 
  the 
  phenomena, 
  but 
  was 
  not 
  applicable 
  to 
  

   all 
  the 
  manifestations 
  of 
  this 
  affection; 
  and 
  it 
  was 
  therefore 
  decided 
  

   to 
  reopen 
  this 
  subject, 
  which, 
  while 
  not 
  as 
  yet 
  of 
  great 
  practical 
  impor- 
  

   tance, 
  may 
  at 
  any 
  time 
  have 
  a 
  bearing 
  on 
  fish-cultural 
  work 
  and 
  aqua- 
  

   rium 
  management. 
  The 
  following 
  data 
  on 
  the 
  symptoms 
  and 
  cause 
  of 
  

   the 
  disease 
  are 
  embodied 
  in 
  a 
  report 
  submitted 
  by 
  Mr. 
  M. 
  C. 
  Marsh, 
  

  

  a 
  Destruction 
  of 
  Trout 
  Fry 
  by 
  Hydra. 
  Bulletin 
  U. 
  S. 
  Fish 
  Commission 
  1902, 
  pp. 
  157-160. 
  

   t> 
  The 
  Gas-bubble 
  Disease 
  oi 
  Fish 
  and 
  its 
  Cause. 
  

  

  