Page 35 - World Aquaculture Magazine - March 2011

World Aquaculture 33
Spawning and larviculture trials of cobia,
Rachycentron canadum (Linnaeus, 1766)
in the United Arab Emirates
Omer M. Yousif, Do V. Minh, K rishna K. Kumar, A bdul-Fatah A. A bdul-Rahman
and Bui V. Hung1
Cobia Rachycentron
canadum, the sole represen-
tative of the family Rachy-
centridae, is a migratory
pelagic species that occurs
in tropical and subtropical
seas except for the eastern
Pacific (Arnold et al. 2002).
It is a gonochoristic species
that has demonstrated the
capacity for high fecundity
and ease of induced and
natural spawning in captiv-
ity (Holt et al. 2007, Benetti
et al. 2008a). They are mul-
tiple batch spawners with a
protracted spawning period
(Faulk and Halt 2003, Benetti et al.
2008b). The information available on
the timing of gonadal maturation in
different parts of the world indicates
that cobia spawn from April through
September with the peak in spring and
early summer (Kilduff et al. 2002,
Faulk and Halt 2003).
Because of the success achieved
around the world in commercial farm-
ing, cobia is sought as a potential
candidate for aquaculture at Abu Al
Abyad Island, Emirate of Abu Dhabi,
United Arab Emirates (UAE). The real
challenge, in such an attempt, is the
ability of cobia to successfully cope
with the harsh conditions prevailing
on the island. The sea water tempera-
ture readings reach as high as 36ºC
and salinity as high as 55 ppt. Despite
this stressful environment, the produc-
tivity of the waters around the island
is surprisingly high (Al Abdessalaam
and Yousif 2002).
Fig. 1. Anesthetized cobia female cannulation.
This article reports the first trials on
the potential of spawning and larvicul-
ture production of cobia at the Aqua-
culture Center, Abu Al Abyad Island
(ACAAB), UAE. The trials were first
conducted usign full strength natural
seawater (51 ppt) of Abu Al Abyad
Island and then later using diluted sea-
water (37 ppt).
Broodstock Management
In 2008 the broodstock, initially im-
ported as fry from Taiwan in 2005 and
grown in marine cages (51 ppt salin-
ity) at ACAAB, were conditioned for
spawning. From October to Decem-
ber 2007 they were fed trash fish and
squid at five percent of body weight
(BW) per day. From January to the
anticipated spawning month of April
2008, the fish were fed trash fish and
squid supplemented with minerals, vi-
tamins and fish oil at 2-2.5 percent BW
per day. During mid-March fish of
both sexes were selected and
transferred to 40 t indoor
spawning tanks (STs). Only
females with cannulated oo-
cytes with an average diam-
eter of ≥ 800µm (Figure 1)
and running ripe males were
selected for spawning. Clove
oil (4-Allyl-2-methoxyphe-
nol) in a dose of 0.01 ppm
was used to anaesthetize
the fish during cannulation
and transportation from the
cages to the STs. Thirty-nine
females averaging 8.4 kg BW
and thirty-ninemales averag-
ing 8.1 kg BW were stocked
in each of the 40 t STs at a ratio of 1:1.
The total number of brooders in each
ST was 6 fish (total biomass per tank
was 50.1 kg). Twenty one females were
left to spawn naturally and 18 females
were induced with a dose of human
chrionic gonadotropin at 1,000 IU/kg
BW. During the spawning period the
water salinity was 55 ppt, water tem-
perature ranged between 24 and 28ºC,
dissolved oxygen ranged between 5-6
ppm and photoperiod was maintained
at 12:12. All spawning, hatching and
larval rearing tanks were plumbed to
a common sand filteration system and
an ultraviolet sterilization unit.
During the 2009 trials, the same
protocol for broodstock management
was followed except that all brooders
were gradually acclimated in the STs
to 37 ppt seawater in the first week of
March. A total number of 15 females
averaging 11.9 kg BW and 30 males av-
eraging 9.3 kg BW (1 female:2 males)