THE EFFECT OF BLOODWORMS AND
ARTEMIA FEEDING ON INDUCED MATURATION AND SPAWNING OF FARFANTEPENAEUS
AZTECUS IN A CLOSED RECIRCULATING SYSTEM
R.L. Gandy, T.M. Samocha
Abstract:
One of the major limiting factors
in the development of a farm-raised live bait-shrimp industry in the U.S. is
the lack of a reliable source of pathogen-free postlarvae (PL). Productions
of PL in the past were based on the collection and spawning of wild gravid
females. The detection of a WSSV-like virus in all native shrimp populations
in Texas waters requires careful monitoring of these spawners to avoid
spreading the disease. A study, funded partially by the USDA Small Business
Innovation Research grant, was initiated to evaluate the feasibility of
developing a PL production center to support the farm-raised live
bait-shrimp industry in Texas. Wild populations of Farfantepenaeus
aztecus were collected in deep waters off the Texas coast. Shrimp were
quarantined for 30 days during which they were screened for infectious
viruses (IHHNV, TSV and WSV). Once cleared by the diagnostic Lab, shrimp
were transferred into three maturation tanks (4 m in diameter each) operated
with a biofilter in a completely closed recirculating mode. Each tank was
stocked with 40 males (20±3.6 g) and 20 females (36±3.3 g). All females in
two maturation tanks were unilaterally ablated by cauterization. Shrimp in
one tank were fed bloodworms (8% of body weight/d) and squid (12% of body
weight/d) while shrimp in the other tank were offered the squid ration and
enriched adult Artemia (8%of body weight/d). Females in the third
tank were not ablated and shrimp were fed the bloodworms and squid rations.
A photoperiod of 12 h light and 12 h dark was maintained throughout the
study. Salinity was kept between 34 and 35 ppt, temperature between 26.5 and
27.0°C. pH between 7.2 and 7.9, ammonia between 0.23 and 1.06 mg/1, nitrite
between 3.08 and 5.98 mg/l, and nitrate at 30 mg/l. Preliminary results
suggest a slightly higher spawning rate per night for the ablated females
that were fed the enriched. Artemia (12 vs. 11% spawns/night).
Although spawn-size was similar among diet treatments 100 K eggs), nauplii
quality of the ablated females fed the enriched Artemia was slightly
better with 15 to 20% higher survival to the first zoea stage than the
bloodworm treatment. Poor spawning rate (1.4%spawn/night) with small
spawn-size (20K/spawn) were found for the unablated females. These results
suggest that wild population of F. aztecus can be induced to mature
and produce viable larvae in a completely closed recirculating system when
females are unilaterally ablated and fed frozen food items.
(Lone Star Farm, P.O.Box 18773,
Corpus Christi, TX 78480 USA, e-mail: rgandy@earthlink.net)