Zudaire et al.: Reproductive potential of Thunnus albacares in the western Indian Ocean 
261 
I 
c n 
r 2,00 
1,95 
- 1,90 
1,85 
1,80 
1,75 
Figure 5 
Mean variation in gonadosomatic index (GSI), hepatosomatic index (HSI), and 
condition factor (K) for Yellowfin Tuna (Thunnus albacares), in our study of the 
reproductive potential of this species in the western Indian Ocean, by oocyte de- 
velopmental stage: primary growth (PG), cortical alveolar (CA), primary, second- 
ary, and tertiary vitellogenesis (Vtg); germinal vesicle migration (GVM); hydra- 
tion (Hydr.), and regenerating (Reg) stage. 
The energy allocation strategy varies among organ- 
isms as an adaptive measure to deal with the fluctua- 
tions in the availability of energy in marine environ- 
ments (Alonso-Fernandez and Saborido-Rey, 2012). 
Subtropical and tropical waters with relatively low 
fluctuations in environmental conditions (e.g., in food 
supply, temperature, and photoperiod) are conducive 
habitats for species to offset the cost of the reproduc- 
tive process by concurrent energy from feeding, with- 
out having to rely entirely on stored energy reserves 
(Alonso-Fernandez and Saborido-Rey, 2012). Yellowfin 
Tuna continue to feed while they reproduce, and it has 
been suggested that the high spawning activity of this 
species depends on prey availability during spawning 
(Itano 2 ). On the basis of our results, we suggest that 
Yellowfin Tuna, like other tropical species (Arrington et 
ah, 2006), requires energy from feeding as well as from 
stored energy to carry out ovarian development. There- 
fore, Yellowfin Tuna could be described as a capital- 
income breeder (Alonso-Fernandez and Saborido-Rey, 
2012), in which the energy stored before reproduction 
is not enough to offset the cost of reproduction, and en- 
ergy allocation from feeding is necessary for successful 
reproduction (Henderson and Morgan, 2002). 
Fecundity estimation 
Few studies have dealt with the fecundity of Yellowfin 
Tuna in the Indian Ocean. In our study, the estimated 
mean BF (3.1 million oocytes) 
is within the range reported by 
Hassani and Stequert, 5 and in 
Table 6 by Timochina and Ro- 
manov 2 for the western Indian 
Ocean and by Sun et al. 6 for the 
western Pacific Ocean. Howev- 
er, our estimate is larger than 
the values reported by Schae- 
fer (1996, 1998) for the eastern 
Pacific Ocean and by Itano 2 for 
the western Pacific Ocean. It is 
lower than the values reported 
by Itano 2 for the Hawaii area. 
Furthermore, the mean BFrel 
value (74.4 oocytes per gram 
of gonad-free weight) deter- 
mined in our study for Yellow- 
fin Tuna is slightly higher than 
the values described by Schae- 
fer (1996, 1998) and Sun et 
al. 6 (Table 6), and it is consid- 
erably higher than the values 
reported by Itano 2 . Besides the 
geographic differences among 
studies, intrapopulation vari- 
ability in fecundity (Schaefer, 
1996) could be the main factor 
that caused the difference be- 
tween the results of our study 
and previously published results. 
The BF increased with female size and weight 
(P<0.05); however, the BF-length and BF-weight rela- 
tionships showed low r 2 (<0.25) with high variability — 
a finding that could result from the asynchrony of the 
population spawning (i.e., with some individuals at the 
beginning and others at the end of their individual 
spawning season). The intercept of the regression line 
between the BF and weight was statistically different 
from zero, indicating that larger females spawn more 
oocytes per gram than smaller females; this dynamic in 
turn would contribute to increasing the egg production 
for large females (Dominguez-Petit and Saborido-Rey, 
2010). However, the BF of fish of the same size varied 
greatly, indicating that other factors, such as fish con- 
dition during spawning, could also drive female produc- 
tivity (Hassani and Stequert 5 ; Murua and Motos, 2006). 
Experiments with captive Yellowfin Tuna showed 
evidence of a positive relationship between the daily 
food ratio and egg batch production (Margulies et al., 
5 Hassani S., and B. Stequert. 1990. Sexual maturity, 
spawning and fecundity of the yellowfin tuna (Thunnus al- 
bacares) of the Western Indian Ocean. Coll. Vol. IPTP (Indo- 
Pacific Tuna Development and Management Program) Doc. 
Vol. 4, p. 91-107. IPTP PO. Box 2004, Colombo, Sri Lanka. 
6 Sun, C., W. Wang, and S. Yeh. 2005. Reproductive biology 
of yellowfin tuna in the central and western Pacific Ocean. 
Western and Central Pacific Fisheries Commission (WCPFC). 
WCPFC-SC1, BI WP-1, 1-14 p. 
