FLOATING SEA HORSE JUVENILES
From: bchadwick@agric.wa.gov.au
Sent: March 31, 2000
QUESTION:
This diagnostic lab has had a case submission involving deaths in sea
horse juveniles, which seems like it must be related to
supersaturation problems in the system to me. The owner feels that he's
ruled out supersaturation however, so I'd like to seek the advice of list
members as to whether there are any suggestions as to whether anything
else may be causing this problem.
Basically the operation in question start losing juvenile sea horses
from the moment they start emerging from the pouch. Affected juveniles
float to the surface with gas in the abdominal cavity and in bubbles under
the skin (as seen histologically) and can never get down again. Some
juveniles float up virtually as soon as they emerge from the pouch, even
before they receive the first feeding, which is given about 24 hours after
the first juveniles emerge. Within 24 hours of the first feeding, about
50% have floated up and been lost, and then losses continue at the rate of
about 50% of what's left each day until they're all gone. By 1-2 weeks
they're always all gone, and this has continued for virtually the whole
time this operation has been attempting to raise sea horses (many months).
Other fish in the system have never been affected by this gas bubble
disease, including the juveniles of other species. The sea horses are in
tanks further from the pump than other species. These facts have convinced
the owner that supersaturation is unlikely, but I can't really see any
other explanation.
Brad Chadwick
Fish Health Section
Fisheries W.A.
c/ AgWA, Baron-Hay Crt
South Perth WA 6151, Australia
Tel. +08 9368 3205
Fax: +08 9474 1881
e-mail: bchadwick@agric.wa.gov.au
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COMMENTS:
I experienced this problem in 1989 in a research project breeding H.
angustus. I submitted samples to Dr Jeremy Langdon (Fish
pathologist) who felt it was probably due to a bacterial infection in
their swim bladders and recommended manipulating husbandry conditions. The
problem was solved by a combination of 1) introducing a protein skimmer to
the system, 2) darkening the tank and 3) placing a dim light at the base
of the tank. The protein skimmer increased the proportion of juveniles
which successfully inflated their swim bladders. Darkening the tank and
adding a dim light improved survival after the commencement of feeding
(i.e. after around 24 hours). Seahorse juveniles were attracted to light
as were the food source we were using (Artemia nauplii). By placing a dim
(actinic) light at the bottom of the tank the juvenile seahorses and
Artemia congregated in the same region at the bottom of the tank and the
juveniles fed and grew well. In contrast, if the main source of light came
from the surface, juveniles skimmed the surface in search of food and
mortalities similar to what you have described were experienced.
Craig Lawrence
Research Scientist (Aquaculture)
Fisheries Western Australia
Fisheries Research Division
WA Marine Research Laboratories
Tel. +61 08 9246 8415
Fax : +61 08 9447 3062
e-mail clawrence@fish.wa.gov.au