518 



Fishery Bulletin 92(3). 1994 



Reproduction 



Gonads of 430 specimens from JA were visually ex- 

 amined macroscopically and classified (based on their 

 size, color, texture, and morphology) as male, female, 

 immature, or unknown. A subsample of these gonads 

 from specimens collected during probable reproduc- 

 tive and nonreproductive periods was removed, wet 

 weighed to the nearest 0.001 g, and preserved in 709£ 

 isopropyl alcohol for further examination. Gonads 

 selected for histology were prepared and embedded 

 by using Kahles solution (Guyer, 1953, p. 236) with 

 a graded series of ethyl alcohol and butyl alcohol 

 dehydration. Embedded subsamples taken from the 

 anterior, middle, and posterior regions of the selected 

 gonads were then sectioned at 5 and 10 urn, mounted 

 on plain microscope slides, and stained by using Dela- 

 field hematoxylin and eosin Y techniques (Humason, 

 1979, p. 112, 119-123). 



Size at first reproduction (SFR) was estimated 

 based on visual examination of gonads and by using 

 the gonadosomatic index (GSI), where: 



GSI = (gonad wet weight/whole body wet weight) x 100. 



The GSI was plotted against SL for male and female 

 M. amaena collected from periods during which the 

 species seemed to be reproductively active. A sharp 

 rise in the GSI at some length indicated the SFR. 

 The SFR was also estimated based on histological 

 examination of gonads from specimens collected dur- 

 ing the April 1984 spawning peak. Eggs were exam- 

 ined for size and stage of development from sections 

 of 11 females representing a range of sizes. Staging 

 was based on size, morphology, and staining proper- 



ties of eggs (Khoo, 1978; Wallace and Selman, 1981). 

 Testes from five males were examined histologically 

 for presence of sperm. 



Spawning season was estimated by plotting GSI 

 against month of capture for 99 sexually mature 

 males and females (larger than 145 mm SL) collected 

 throughout the sampling period. Histological sections 

 of samples from March, April, May, July, and August 

 1984 were examined for further validation of repro- 

 ductive periods. 



We did not identify individual clutches of ova in 

 females. Based on the histology, we identified ova 

 >0.4 mm on the major axis as being in an advanced 

 stage of yolk development and defined this stage as 

 mature (Table 1, See Fig. 3). Our fecundity value is 

 an estimate of the number of such ova in a female 

 specimen. Ovaries from 12 gravid females collected 

 at JA during the January 1986 spawning peak were 

 used to estimate fecundity. Three 0.02-g aliquots were 

 taken from the midsection of each ovary. All mature 

 ova (>0.4 mm on the major axis) were counted with 

 the aid of a binocular dissecting microscope. Fecun- 

 dity, F, was estimated for each female from the formula: 



F=W 1 +N 2 +N 3 )/3)x(G/A), 



where N l ,N. 2 , N 3 = the number of mature ova in each 

 aliquot; 



G = total gonad weight (g); 



A - weight of a gonad aliquot (0.02 g). 



For specimens from Puako, the same procedures 

 were followed except that no histological prepara- 

 tion or examination was done, and ripeness was es- 

 timated simply on the basis of visual appearance of 



