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Fishery Bulletin 91(2). 1993 



in the month of October, and would coincide with the 

 spring warming of water in Cleveland Bay after low 

 winter temperatures which begin to rise in August/ 

 September (Kenny 1974, Walker 1981). Highest GSI 

 values were also reported for male and female L. 

 vulgaris during the spring period in the Mediterra- 

 nean (Worms 1983). 



The interpretation of fluctuations in the GSI and 

 NGL/DML index is complex due to a variety of fac- 

 tors: (1) L. chinensis exhibits fast growth and has a 

 short lifespan, therefore annual data sets reflect a num- 

 ber of different generations of squids; (2) because of 

 rapid growth and the observed variability in gonad 

 growth (especially in females), greater sample num- 

 bers would be needed to adequately describe gonad 

 growth fluctuations on a smaller scale (e.g., intra- 

 monthly variability); (3) due to the tropical nature of 

 the environment, squids (especially males) are mature 

 throughout most months of the year and, therefore, 

 gonad indices are generally reflecting periods of greater 

 investment in reproductive structures rather than pe- 

 riods of immaturity vs. maturity. 



The data peaks in October may have been due to 

 the increasing day length in spring, stimulating the 

 optic gland to produce increased hormonal levels which 

 accelerates gonad growth (see Mangold 1987). Since 

 day length would be shortened over the winter period 

 (June- August), the increasing day length during the 

 spring period, along with increasing water tempera- 

 tures, may produce physiological responses leading to 

 maximal gonad growth. More intensive sampling (e.g., 

 fortnightly) over the late-spring and early-summer pe- 

 riod may provide a clearer picture of relative gonad 

 growth over this period. The relationship between 

 mantle length and NGL could constitute a good matu- 

 rity index for females, since the relationship between 

 NGL and DML is closer than the relationship between 

 DML and gonad weight (Worms 1983). Data for fe- 

 males of L. chinensis from this study suggest that the 

 NGL/DML index provides results very similar to GSI 

 values. Maturity parameters based on NGL alone could 

 constitute a more convenient means to determine ma- 

 turity for tropical squids. 



Nidamental gland length The fact that length of the 

 nidamental gland of L. chinensis bears a very close 

 resemblance to growth of the gonad highlights the close 

 association this organ has with maturation and egg 

 development. The nidamental gland serves the func- 

 tion of producing a gelatinous matrix which encases 

 the cephalopod egg (Roper et al. 1984). Previous stud- 

 ies have used the NGL/DML ratio as a convenient 

 means to assess maturity. Temperate loliginids have 

 been shown to possess mature oocytes when this ratio 

 is >0.2 (Yang et al. 1986, Hanlon et al. 1989). This 



relationship generally holds well for females of L. 

 chinensis. Out of 112 females (captured throughout 

 the 2yr sampling period) analyzed for this ratio, all 

 the mature females had an NGL/DML ratio >0.2. Of 

 the immature females analyzed, six individuals (5.4%) 

 had a ratio >0.2 (highest value=0.26). This parameter 

 therefore appears to be useful for tropical loliginids as 

 well. The 0.2 NGL/DML ratio does appear to be the 

 minimum parameter for mature females. 



Nidamental gland measurements are thus useful for 

 providing a rapid and convenient means of assessing 

 the level of maturity in tropical loliginids. The nida- 

 mental gland can also provide useful information about 

 the past history of a female squid. The fact that some 

 of the larger, older, immature females captured during 

 January had small underdeveloped nidamental glands 

 was one means to ascertain that these females had 

 actually not yet matured and had not regressed from a 

 previously mature condition. 



Hectocotylus length The hectocotylus is an impor- 

 tant reproductive structure employed by the male to 

 pass spermatophores to the female during copulation. 

 It is also extremely useful for quick sexual identifica- 

 tion of preserved specimens. Coelho et al. (1985) car- 

 ried out a detailed study of the growth of the hecto- 

 cotylus of Illex illecebrosus to determine if the degree 

 of hectocotylization of the fourth arm could be related 

 to maturity. However, no close relationship was found 

 between maturity and the degree of hectocotylization. 

 A partial explanation for this lack of relationship be- 

 tween these parameters was attributed to the fact that 

 the squids examined might have included individuals 

 which hatched at different localities and which had 

 developed under different temperature regimes (e.g., 

 some squids could have been immigrants from a more 

 southerly population exposed to warmer temperatures). 

 This could well account for considerable confusion in 

 the Illex data, as individuals of L. chinensis from dif- 

 ferent seasons showed a different relationship between 

 hectocotylus length and mantle length, and hectocotylus 

 length and age. These seasonal growth patterns which 

 were temperature-related did have an influence on the 

 development rate of the hectocotylus, with slower- 

 growing individuals eventually possessing a larger 

 hectocotylus than their faster-growing counterparts. 

 Different-sized hectocotili on similar-sized squids could 

 therefore indicate that the squids had developed un- 

 der different growth rates. This also suggests that the 

 size ratio of many other structures to body size may 

 also be influenced by the ambient temperature in which 

 the squid develops. Parameter ratios and indices used 

 for taxonomic purposes should therefore be cautiously 

 employed, at least for nearshore squids, and, when- 

 ever possible, parameters should be measured in 



