Page 5 - IJA-Vol.3-No.12

International Journal of Aquaculture, 2013, Vol.3, No.12, 55-62
http://ija.sophiapublisher.com
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was from 1st July to 25th July, corresponding to the
temperatures ranging from 21.0 ℃ to 22.0 ℃. The
mean diameter of the eggs was (0.607±0.03) mm, and
a total of 4.345 million eggs were collected through
the spawning season, of which 2.845 million were
considered as well developed (Figure 1). 1.8 million
newly hatched larvae were obtained in this study, and
the hatching rate was 41.7%.
Figure 1 Spawning frequency and egg numbers produced by T. modestus
Like most species from the family of Monacanthidae,
the eggs of bluefin leatherjacket were subjected to
adhesive egg. The adhesiveness of eggs from
Monacanthidae is very strong (Zhao et al. 1985). In
nature, this type of eggs was normally adhered to the
substrate such as reef, algae and cay. There are a large
number of viscin threads distributing on the egg
surface of bluefin leatherjacket (Zhao et al. 1985;
Safran and Omori 1990). Previous studies indicated
that by using viscin threads the fertilized eggs of
bluefin leatherjacket can stick on the substrates such
as shell, coral reef, large algae, and rocks in the
natural environment (Qian 1998; Su and Li 2002).
Results from our previous investigation indicate that
the plastic plate and black soft plastic film attracted
more eggs in the artificial breeding environment, and
the viscin threads of eggs were not well stuck to the
rough surface materials (Guan et al. 2012). Therefore,
plastic corrugated plates were used to collect the eggs
in the present study.
In order to manipulate the natural hatching environment
and reduce human interruption, after eggs collection,
the eggs’ together with attached plastic corrugated
plates were directly incubated in the larval rearing
tanks without any treatments. Because of the
characteristic of sticky, the fertilized eggs were easily
to be lumped with sands or other substrates. Copepods
and nematodes were observed living on the egg lumps
in the present study. The hatching rate was only
41.7%, which was lower than those species with
floating eggs (Ma et al. 2012a; Nocillado et al., 2000).
It is unclear whether the hatching rate was affected by
lump-forms and parasites in the present study. In order
to increase the hatching rate, future research should
towards developing the hatching protocols for
adhesive eggs, and technology such as eggs debonding
should be considered in the future study.
1.2 Description of Development During Endogenous
Feeding Period
After approximate 1 h 30 min, fertilized eggs entered
into 2-cell stage, and 32-cell stage was recorded at 3 h
25 min (Table 1, Figure 2). After 6h further development,
the fertilized eggs entered into blastula stage, the
accumulated temperature reached to 132.93 (℃×h). When
the accumulated temperature reached to 210 (℃×h),
fertilized eggs entered into gastrula stage. After 48h
development when the accumulated temperature reached
to 1 000 (℃ ×h), fertilized eggs became pre-hatch
embryo, and 50% eggs hatched when the accumulated
temperature reached to 1050 (℃ ×h) (Table 1, Figure 2).
1.3 Yolk and Oil Globule Absorption
Growth and morphological characteristics of the
larvae during the first five days are presented in Table 2.
The mean total length (TL) of newly hatched larvae
was (2.08±0.09) mm with an ellipsoid yolk-sac of
(0.5331 ±0.0366) mm long and (0.2593±0.0393) mm
wide. One oil globule with the diameter of (0.20±0.01) mm
was presented at the anterior end of the yolk-sac. After
hatching, fish larvae had un-pigmented eyes, and the
mouth did not open. Melanophores were presented on
the snout tip, the trunk and on the tissue surrounding
the inner side of the yolk-sac. Xanthophores were
presented on the trunk, abdomen and around the head.
The mouth opened on 3dph, while first feeding was