Sun et al.: Reproductive biology of Makaira nigricans 
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Oocyte diameter (microns) 
Figure 7 
Frequency distributions (percentages) of oocyte diameter (black solid lines) with 
95% bootstrapped confidence intervals (gray dashed lines) for six ovarian developing 
stages of blue marlin (Makaira nigricans ): (A) immature; (B) resting; (C) maturing; 
(D) mature; (E) spawning-spawned; and (F) recovering. CN, chromatin nucleolar 
oocytes; PN, perinucleolar oocytes; PV, previtellogenic oocytes; VT, vitellogenic 
oocytes; HY, hydrated oocytes; UO, unovulated hydrated oocytes. 
Ocean, the spawning season for blue marlin is May 
through September, but most activity is between July 
and August according to data collected near Puerto 
Rico (Erdman, 1968), although Yeo (1978) indicated 
that blue marlin spawn at temperatures of 26-29°C 
from April to September in the western North Atlantic. 
These estimates of spawning season would indicate 
that blue marlin have an extended spawning season 
and may be more reproductively active during summer, 
perhaps because of higher temperatures at that time. 
Batch fecundity 
It has been argued that more accurate estimates of 
batch fecundity can be obtained by using only oocytes 
in the migratory nucleus and hydrated stages (sailfish, 
Istiophorus platypterus\ Chiang et al., 2006a). Unfor- 
tunately, few ovary samples with migratory nuclei or 
hydrated oocytes were observed in our study. However, 
the oocyte distributions exhibited clear modes, includ- 
ing oocytes at sizes that are ready to be spawned. The 
oocyte size-frequency method usually yields results 
similar to those based on counts of hydrated oocytes if 
females with highly advanced oocytes are used (Hunter 
et al., 1985). In this study, the gonad tissues were col- 
lected and preserved for further examination. Batch 
fecundity is usually back-calculated gravimetrically 
as the product of the oocyte density per gram of the 
preserved tissue and the total fresh weight of the ovary. 
However, Ramon and Bartoo (1997) indicated that 
preserved ovaries of mature albacore tuna ( Thunnus 
alalunga) lost an average of 2% of their fresh weight. 
The effect of preservation on weight lost may bias 
the estimation of batch fecundity by the gravimetric 
method and may also bias identification of the most 
advanced-stage oocytes. Thus, gonad weights for fresh 
