YANG ET AL.: CULTURE EXPERIMENTS OF LOLIGO OPALESCENS 



restricted diet offered to them may have influenced 

 that. Fields (1965) and Karpov and Cailliet (1978) 

 agreed that L. opalescens adults prefer fish over 

 crustaceans but there was no clear-cut preference 

 in younger squid. It is clear from laboratory obser- 

 vations that squid learned to associate certain events 

 with feeding (e.g., opening the tank top), and the 

 general level of activity increased markedly during 

 these periods. We were also able to stimulate 

 feeding in the CT systems by dimming and bright- 

 ening the lights to attract the planktonic food 

 organisms into the water column near the squid. 



Schooling behavior was correlated with size. 

 Larger body size and growth of the fins were re- 

 quired before squid could swim in place against a 

 current; this occurred at about 10 mm ML (41-44 

 d in L.O. 1981 and 1982). Hurley (1976) reported 

 that L. opalescens 4 to 5 mm ML could briefly form 

 loose schools when disturbed, but this may have 

 been in static water. At 15 mm ML, L. opalescens 

 were powerful enough to form distinct schools (Yang 

 et al. 1983a), indicating the size at which one could 

 expect schooling to appear in nature. How and why 

 squid begin schooling in nature has not been 

 investigated. 



Cannibalism was not seen in L.O. 1980 (Yang et 

 al. 1980b, 1983a) and accounted for 7 to 19% of mor- 

 talities in experiments L.O. 1981 and 1982. Lack of 

 food did not precipitate this behavior. On the spawn- 

 ing grounds in Monterey, CA, mature squid often 

 have cephalopod remains in their stomachs (Lou- 

 kashkin 1977; Karpov and Cailliet 1978); in one case 

 as many as 75% of males had squid remains in their 

 stomachs (Fields 1965). This could be a behavioral 

 response to overcrowding (Fields 1965) or to restrict 

 prey organisms on the spawning grounds. We anti- 

 cipate that cannibalism in tanks would be a signi- 

 ficant problem only during prolonged food shortage 

 or if squid of a very wide size range were in the same 

 system (cf., Hanlon et al. 1983). 



Body patterning was not studied in great detail 

 but several observations are noteworthy. Young 

 animals are capable only of simple chromatic expres- 

 sion such as "All dark" or "Clear". When excited, 

 L. opalescens of all sizes show some degree of dark- 

 ening; this is similar to other loliginid squids (cf., 

 Hanlon 1982; Hanlon et al. 1983). By the time the 

 squid are approximately 80 to 100 mm ML they can 

 show a repertoire that includes about a dozen 

 chromatic components of patterning (e.g., Dark arm 

 tips, Ring on the mantle, etc.). This places L. 

 opalescens in a category of rather simple pattern- 

 ing, making it comparable to L. pealei and L. 



vulgaris, slightly more complex than Lolliguncula 

 brevis (Dubas et al. 1986), but simpler than Loligo 

 plei (Hanlon 1982; Hanlon et al. 1983). Further 

 analysis is warranted because much behavior is ex- 

 pressed through patterning and may yield impor- 

 tant behavioral clues. 



Social behavior was first manifest in schooling (see 

 above) then much later in mild intraspecific aggres- 

 sion. Occasionally two squid would fight over one 

 fish, but the first firm observations came at the time 

 of sexual maturation when mating was seen. As 

 Hurley (1977) noted, there were no obvious inter- 

 actions among males to form a dominance hierarchy 

 for mate selection. Mating was initiated by males, 

 and both typical forms of mating were observed: 

 "head-to-head" matings in which spermatophores 

 were stored in the bursa copulatrix; and male- 

 underneath matings in which spermatophores were 

 deposited in the mantle near the oviduct (cf., Drew 

 1911; McGowan 1954; Hurley 1977). Females mated 

 promiscuously as they do in nature, and females 

 were also stimulated visually to lay eggs around ar- 

 tificial facsimiles of egg mops (Fig. 16). Males were 

 not observed to guard or defend egg capsules as 

 described by Hurley (1977), but this may have been 

 because relatively few egg capsules were left in the 

 tank each day. 



Reproduction 



In L.O. 1980 only the subadult stage was reached 

 in 233 d (Yang et al. 1980b, 1983a). Full sexual 

 maturity was achieved in L.O. 1981 and 1982 and 

 spawning of viable eggs occurred from days 196 to 

 239 and 175 to 226, respectively (Fig. 13). Relatively 

 few egg capsules were laid per female, and these 

 capsules were generally shorter and contained 

 slightly fewer eggs per capsule than those reported 

 from natural populations, but this was probably due 

 to the smaller size of these spawning females (Hixon 

 1983). 



Laboratory cultured Loligo opalescens matured 

 precociously and since they are terminal spawners 

 this prevented attainment of full adult size. In the 

 laboratory, males as small as 71 mm ML had fully 

 formed spermatophores and females became sexual- 

 ly mature beginning at about 60 mm ML (Fig. 15). 

 In nature, the average adult size is 150 mm ML for 

 males and 140 mm ML for females, although size 

 at onset of maturity is variable and can be as low 

 as 72 mm ML for males and 81 mm ML for females 

 (Fields 1965; Hixon 1983). Precocious maturation 

 has also been reported in other squid maintained in 

 the laboratory (cf., Durward et al. 1980; Hanlon et 



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