FISHERY BULLETIN: VOL. 87, NO. 4, 1989 



154.31). Interesting to note was the propensity 

 for decreasing mean GSFs in uku larger than 600 

 mm FL (Fig. 5). 



In contrast, the smallest mature onaga was 

 522 mm FL (2.22 kg) or 53.9% MAXLEN, and 

 ripe individuals were not encountered until 605 

 mm FL (3.22 kg) or 62.4% MAXLEN. The pre- 

 dicted value of L50 obtained from the logistic fit 

 of percentage mature on FL was 663 mm FL (a 

 = -0.0233, b = 15.462; Fig. 6), and 77% of the 

 onaga in the 675-725 mm FL class were found to 

 be at stage II of development or beyond (Table 

 2). Onaga spawned over a narrower size range 

 (600-900 mm FL; Fig. 5) compared with uku 

 (450-1,050 mm FL; Fig. 5). 



Histological examination of ovaries indicated 

 that both species follow a similar pattern of de- 

 velopment (Fig. 7). The progression from 

 oogonia to hydration is typical of snappers and 

 has been covered in detail by Crossland (1977) 

 and Wallace and Selman (1981). Postovulatory 

 follicles were not identifiable in tissue sections 

 from ripe (stage III) ovaries of either species. 

 None of the immature (stage 1) ovaries examined 

 histologically showed signs of atresia, indicating 

 that these fish had not previously spawned. 

 Identifiably atretic individuals in later stages of 

 development were not observed until the end of 

 the spawning season. 



Spawning Frequency and Pattern of Egg 

 Release 



The size-frequency distributions of oocyte di- 

 ameter were constructed for ovaries of uku 

 caught during the spawning season, using the 

 volumetric method, and were found to be poly- 

 modal, suggesting that uku may release multiple 

 egg batches (Fig. 8a). All ovaries possessed a 



Ami. 



m 







Figure 7. — Photomicrographs showing transverse histological sections of uku and 

 onaga ovaries in various stages of development. Scale bars represent 0. 10 mm. A. 

 Early developing uku (386 mm FL) ovary classified as juvenile (stage I) containing 

 numerous previtellogenic (PV) oocytes. Larger oocytes (LO) have reached the 

 lipoid or yolk vesicle stage, just prior to vitellogenesis. B. Developing (stage 11) 

 uku (525 mm FL) ovary. Shown are previtellogenic (PV) and vitellogenic (VT) 

 oocytes. C. Ripe (stage III) uku (541 mm FL) ovary with hydrated (HY) oocytes. 

 Lipoid vesicles have fused to form a single mass (LV). D. Juvenile (stage I) onaga 

 (506 mm FL) ovary consisting of previtellogenic (PV) oocytes with large central 

 nucleus (NU) containing numerous nueleoh (NC). E. Developing (stage II) onaga 

 (753 mm FL) ovary showing numerous mature oocytes in different stages of vitel- 

 logenesis (VT). F. Enlargement of a developing onaga ovary. Shown are gran- 

 ulosa (GR) and thecal (TH) cell layers, zona radiata (ZR), and yolk gi-anules 

 (YG). G. Ripe (stage III) onaga (605 mm FL) ovary showing hydrated (HY), 

 vitellogenic (VT) and previtellogenic (PV) oocytes. 



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