Ramon and Bailey Spawning seasonality of Thunnus alalunga 



727 



methods described in Hunter et al. (1986). A cross 

 section of the ovary was taken from the middle re- 

 gion of the ovary, dehydrated, embedded in paraffin, 

 sectioned at 7 ^m, and stained with Harris's hema- 

 toxylin followed by eosin counterstain. The slides 

 were examined with a compound microscope to de- 

 termine the stage of ovarian development (as char- 

 acterized by the presence or absence of yolk, lipid 

 vesicles, hydrated oocytes, and postovulatory fol- 

 licles) and were classified as early developing 

 (unyolked), late developing (partially yolked), or ad- 

 vanced (fully yolked) (Schaefer, 1987). A second cross 

 section of ovarian tissue was taken from the outer 

 edge of the ovary to the lumen. This sample was 

 placed in 33% glycerol for 10 to 20 minutes to sepa- 



rate the oocytes from the ovarian connective tissue 

 (Hunter et al., 1986). The separated oocytes were then 

 measured to 0.01 mm to determine the average size 

 of the most developed stage of oocytes in each ovary; 

 this was done by measuring the diameter of 20 oo- 

 cytes in the sample as described by Schaefer (1987). 

 The mean diameter of the most advanced stage of 

 oocytes was plotted against months to examine the 

 seasonal trend of maturity (Fig. 2). Oocyte diameter 

 and developmental stage of the ovaries were exam- 

 ined to see if differences in weight between the right 

 and left sides of the ovary were associated with dif- 

 ferences in the reproductive state. 



The histological condition of the samples did not 

 provide the resolution necessary to distinguish 



« E 



V, E 



o — 



E % 



S S. 



JUL AUG SEP 



OCT NOV DEC JAN 



MAR APR MA 



Figure 2 



Monthly variation in mean diameter of the most advanced stage of oocytes 

 for albacore, Thunnus alalunga, sampled from New Caledonia and Tonga, 

 1990 to 1992 (±2 standard errors; n=97). Numbers above error bars indicate 

 the sample size for each month. 



