| Larval stages of many
teleost fishes contain both ovarian and testicular tissue, and sexual differentiation
begins shortly after hatching or initiation of feeding. Several techniques
(e.g., manual separation, hybridization, and sex reversal via steroid administration)
have been developed for the control of sexual differentiation in fishes,
and there are pros and cons to each technique. Tilapia generally attain
sexual maturity at age 3 - 6 months and begin to reproduce immediately,
which causes a variety of problems for the production of tilapia for market.
Consequently, strategies for the production of monosex (i.e., male) tilapia
populations are being developed.
The primary goal of studies
conducted under INAD #11-236 is to generate data evaluating the efficacy
of
17 alpha-Methyltestosterone (MT) administered in feed to larval tilapia
to produce populations comprised of >90% male fish. Under this INAD,
Hawkins, Inc., Pharmaceutical Group (Minneapolis, MN), is the only authorized
manufacturer of MT, and Rangen, Inc. (Buhl, ID), is the only authorized
supplier of MT-medicated feed to all Investigators. One treatment option
is allowed (see below). Withdrawal requirements (days or individual fish
weight) depend on whether fish are reared in a “batch culture”
system (120-d withdrawal period) or a “partial-harvest/restock culture”
system (individual fish must weigh at least 350 g before being slaughtered
for market).
| Treatment
option: Administer MT at a dose of 9 mg active drug/kg of fish biomass.
MT will be incorporated into tilapia feed by Rangen, Inc. at a rate
of 60 mg MT/kg feed. Therefore, based on standardized procedures for
tilapia production, newly hatched tilapia fry should be fed 150 g
MT-medicated feed/kg fish biomass/day (i.e., fed at 15% body weight
daily). MT-medicated feed should be fed to tilapia fry for 28 consecutive
days. No retreatment will be allowed. |
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