Metamorphosis
in summer flounder: manipulation of thyroid status to synchronize settling
behavior, growth, and development
S. Gavlik, M. Albino, J.L. Specker-2002
Aquaculture, 203(3-4): 359-373
Abstract:
In the aquaculture of summer flounder (Paralichthys
dentatus), the inherent variation in growth and settling behavior during
metamorphosis may lead to cannibalism and necessitate increased labor due to
grading. Our goal was to use thyroid hormone manipulation to synchronize
settling behavior and produce a uniformly sized cohort of juvenile summer
flounder. Premetamorphic flounder were treated with exogenous thiourea (TU,
30 ppt, an inhibitor of thyroxine (T4) synthesis). Following removal of TU,
metamorphosing flounder were exposed to either exogenous T4 (T4-Na salt, 100
ppb, dissolved in DMSO) or DMSO only. A control (no TU, then DMSO only, when
appropriate) was used for comparison. Settling behavior in the control was
prolonged, with the Peak Settlement Interval (defined as the interval
beginning on the day the first 20% settled until the day 80% had settled)
requiring 9 days, and a settling rate of 4.1±0.2 fish/day. Settling
behavior was synchronized by thyroid hormone treatment. The Peak Settlement
Interval was reduced (5 days) and settling rate increased (8.5±0.6
fish/day) by TU treatment. Treatment with TU followed by T4 further reduced
the Peak Settlement Interval (3 days) and increased settling rate (11.2±0.6
fish/day). Development rate (DR) and growth rate (GR) were reduced by TU
treatment, but following TU with T4 treatment restored DR and GR to control
levels. However, TU treatment eliminated the larger, potentially
cannibalistic juveniles found in control tanks. Both treatments reduced
variance in GR, whereas only TU-T4 reduced variance in DR. Percent survival
was unaffected by treatment. In aquaculture, the effective synchronization
of settling behavior by thyroid hormone manipulations should reduce the
labor costs associated with grading. We recommend a treatment regime that
could aid in the production of more uniform cohorts of juvenile summer
flounder.
(Graduate School of Oceanography, University of Rhode
Island, Box 200, 218 South Ferry Rd., Narragansett, RI 02882, USA, Tel.:
+1-401-874-6820; fax: +1-401-874-6887, e-mail of S. Gavlik: sgavlik@gso.uri.edu,
e-mail of J.L. Specker: jspecker@gso.uri.edu)