808 



Fishery Bulletin 97(4), 1999 



Discussion 



This study describes the pattern of allocation of re- 

 sources to the growth of somatic and reproductive 

 tissues in Sepia pharaonis, one of the two most com- 

 mercially important cephalopods in the Suez Canal 

 and northern Indian Ocean. This study indicates that 

 gametogenesis is fueled by energy and nutrients de- 

 rived from the diet rather than from reallocation of 

 somatic reserves. Two complementary methods 

 (analysis of covariance and multivariate regression 

 on the entire data set) and the monthly changes in 



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50 



40 



30 



20 



I i i I 



N94 J M M J S N95 J M 



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N94 



M 



M 



N95 



Figure 3 



Female Sepia pharaonis mean (SD) dry weight indices of mantle (MI) 

 head (HI), viscera (VI), digestive gland (DGI), nidamental gland (NGI) 

 and gonad masses (GSI) for standard size (110-1.30 mm MLi. 



dry weight of somatic indices of a restricted size range 

 showed essentially similar patterns of maturation. 

 Sexual maturation in Sepia pharaonis affected 

 males and females differently. Forsythe and Van 

 Heukelem (1987) suggested that male maturity in 

 cephalopods was achieved at little cost to somatic 

 growth and that, in most cases, males continue to 

 grow after reaching maturity. Changes in male so- 

 matic mass do not appear to be related to maturity. 

 At full maturity in males, dry weight of reproduc- 

 tive and accessory reproductive tissues accounted for 

 only 2.6% of the total somatic dry weight. However, 

 these tissues accounted for approxi- 

 mately 16*^ in females. For both sexes, 

 somatic growth was completed by late 

 October as the average mantle mass and 

 head mass components reached maxi- 

 mum weights. 



In females, spawning occurred from 

 spring throughout the summer, and the 

 end of spawning activity was reflected 

 by a sharp drop in the average gonad 

 weight index in October (Fig. 3) . Thus 

 spawning occurred at the time of in- 

 creasing temperature and food avail- 

 ability (Gabr, unpubl. data). There was 

 no evidence of decline in feeding rate 

 with maturation. This finding suggests 

 that gonadal growth may be supported 

 directly by the assimilated food ration, 

 although some diversion of resources 

 into reproduction at the expense of so- 

 matic growth also occurred. This diver- 

 sion of resources was indicated by a 

 small but significant decrease in mantle 

 and head mass with maturation (Fig. 2), 

 and the inverse relationship of mantle 

 . and head mass with gonadal indices 

 (Fig. 3). 



There is some evidence to support the 

 idea that female Sepia pharaonis may 

 feed, grow, and mature simultaneously 

 in the field. For example, no spent fe- 

 males were caught at any time of the 

 year. This may be because it is difficult 

 to differentiate spent females from ma- 

 ture ones if spent females remain in 

 good condition (because they continue 

 to feed when mature). Because females 

 need a greater energetic reserve for re- 

 production, they grow faster than males 

 and reach a maximum size of 240 mm 

 ML, whereas the maximum size for 

 males was 170 mm ML. Sepia pharaonis 

 spawns in shallow water and migrates 



M 



