Beberapa aspek men genai biologj pembiakan tuna, thunnus albacares (bonnaterre)
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Date
1995
Authors
Sok Kean, Khoo
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Abstract
The reproductive biology of yellowfin tuna, Thunnus
albacares (Bonnaterre) , caught from the eastern par"c of
the Indian Ocean at the latitude of 0 - 10° N and
longtitude of 80 - 95° E were studied. Gonads of this
fish weLe taken from Taiwanese tuna lortgline vessels at
the Penang Harbour from October 1992 to September 1993.
Histological and histochemical examinations were used to
determine the sexual development of both male and female
gonads.
The testis of yellowfin tuna is of the restricted
spermatogonial testis-type. This is not typital of most
teleosts as its spermatogonia were restricted to the
1 distal terminus of the tubules immediately beneath the
tunica albuginea.
Oogonia and oocytes in the pre-vitellogenesis stage
showed similar features as those of other teleostean
fishes. However, the vitellogenesis phase was
significantly different from that of other fishes as the
yolk vesicles stage did not occur and therefore cortical
alveoli was absent in the oocytes. Vitellogenesis (~f
the yellowfin tuna was characterized first by the
appearance of lipoid yolks, which 'occupied the
cytoplasmatic region around the nucleus. Subsequent to
this, yolk granules began to appear in the peripheral
region of the cytoplasm. Eventually, lipoid yolks grew
bigger and fused to become oil dropl~ts in the middle
of the oocyte, while yolk granules went through the same
growing and fusing process to become yolk platelets
which were ~pushed' to the periphery of cytoplasm by the
oil droplets.
Studies on the gonadosomatic index (GSI) of yellowfin
tuna indicated that they are annual spawner and that
their peak spawning season extended from February to
April each year. The peak season was complemented·by
the results from the measurements of mean diameter of
oocytes. These studies also showed that yellowfin tuna
is a multiple spawr.ar which spawns at least twice during
the spawning season.
Similar values of GSI do not necessarily mean that the
gonads are at the same stage of sexual development. In
this study, the mean GSI were almost the same for the
months of November and June for the male fish, and
November with May for the females; Detailed
histological observation showed that these fish were at
different phases of reproductive cycle though. I?uring
the month of November, the fish was in the middle of the
pre-spawning period while in the months of May and June,
they were at the post-spawning period. For the male
fish, the post-spawning period could be distinguished
from the pre-spawning period by the presence of empty
lumens in the testis where spermatozoa did not exist or
only present in a very small number, while for the
females, the presence of post-ovulatory follicles was a
very good indicator of the post-spawning period.
The reproductive cycle of yellowfin tuna appeared to be
influenced by the North and South Equatorial Currents
which created the Intertropical convergence Zone during
the months of January and February in the area of study . .
The re~filting upwelling may induced the fish to spawn
during this period. The Indian Monsoon season which
brought heavy rain from the months of June to September
may also played an important role in the seasonal
reproductive cycle of the yellowfin tuna in the Indian
Ocean.
Description
Keywords
Biologj pembiakan tuna , Thunnus albacares (bonnaterre)