FISHERY BULLETIN: VOL. 84, NO. 4 



squid abundance would enhance survival, but no 

 change has been observed. Further experimentation 

 is required, but a central question is whether many 

 squid are genetically unfit to survive or whether we 

 have not yet provided the proper foods and environ- 

 ment for good survival. Although the former pros- 

 pect seems unlikely from the evolutionary viewpoint, 

 our experimental design has certainly promoted 

 outstanding growth in surviving squid. 



With the growth data from live squid in L.0. 1982, 

 we confirmed that squid grow exponentially both by 

 weight and length during the first 2 months (Fig. 

 9). Weight increases at a rate of 8.35% body 

 weight/day (doubling their weight every 8 d) and this 

 compares very favorably with octopods (4-7%), other 

 squid (5-7%), and cuttlefishes (5-12%) (Forsythe and 

 Van Heukelem in press). Logarithmic growth dur- 

 ing the rest of the life cycle also conforms general- 

 ly to other cephalopods, except that some cepha- 

 lopods have a longer exponential growth period up 

 to one-half their life cycle (Forsythe and Van 

 Heukelem in press). The length-weight relationship 

 (Figs. 10, 11) generally conforms to those of wild- 

 caught squid, but indicates that laboratory-reared 

 squid weigh more per unit length (Table 3), possibly, 

 as a result of reduced swimming. The slopes of the 

 lines (all <3.0) indicate allometric growth (Forsythe 

 and Van Heukelem in press). The estimated feeding 

 rates of 18.0% body weight/day (days 121-176) in 

 L.O. 1982 and 14.9% (days 108-230) in L.O. 1981 

 compare well with the estimate of 14.4% (on a dry 

 weight basis) for L. opalescens of a similar size in 

 the natural population (Karpov and Cailliet 1978). 

 Younger L. opalescens (48-56 d) fed on Artemia 

 were estimated by Hurley (1976) to feed at rates of 

 36 to 80%/day (dry weight). Another loliginid squid, 

 Sepioteuthis sepioidea, had feeding rates of 20 to 

 25% (wet weight) between days 70 and 105 (La Roe 

 1971). Other squids of similar size show comparable 

 rates: Loligo plei, 10 to 18% (Hanlon et al. 1983); 

 L. pealei, ca. 11% (Macy 1980); Illex illecebrosits, ca. 

 10% (Hirtle et al. 1981); and Todarodes pacificus, 

 ca. 24% (Soichi 1976). 



Maximal survival and size in our three major ex- 

 periments were L.O. 1980 - 233 d, 77 mm ML (Yang 

 et al. 1983a); L.O. 1981 - 248 d, 113 mm ML; L.O. 

 1982 - 235 d, 116 mm ML. Figure 13 illustrates sur- 

 vival throughout these experiments and shows that 

 there was a long, steady mortality after the initial 

 high mortality of the first 2 wk. Once in the RW 

 systems (i.e., after 2 mo) most mortality was attrib- 

 uted to fin and skin damage (Hulet et al. 1979; Fig. 

 14) that accrued slowly from colliding with the sides 

 of the tank. The painted designs on the walls were 



clearly helpful in reducing wall collisions but damage 

 over time was lethal in many squid. Cannibalism ac- 

 counted for a minor number of deaths (ca. 7-10%) 

 Most mortality after day 170 in L.O. 1981 and L.O. 

 1982 was due to 1) sexual maturation and spawn- 

 ing and 2) an unusual situation where fully mature 

 females scraped the bottom of the tank often enough 

 to wear a large lesion through the ventral mantle 

 (Fig. 14C). 



It should be noted that survival rate was greater 

 where large tanks such as the RW were used. In 

 L.O. 1981 (Fig. 13A), 50% survival of squid left in 

 the smaller CT system occurred only on day 84 

 compared with day 114 for those transferred to the 

 RW. 



In summary, growth was excellent, indicating that 

 estuarine foods were sufficient and that system 

 design and water quality were conducive to growth, 

 especially in the first 2 mo. Survival was good from 

 the historical perspective (cf., Arnold et al. 1974; 

 Yang et al. 1983b) but rather poor from the produc- 

 tion standpoint. A recent hypothesis concerning 

 temperature effects on growth (O'Dor and Wells in 

 press) indicates that higher temperature in the first 

 half of the life cycle and lower temperature in the 

 latter half may enhance growth and survival of 

 laboratory-reared squid. In future work it would be 

 desirable to enhance growth during the latter half 

 of the life cycle and to provide an environment in 

 which somatic growth continues for a longer period 

 before sexual maturation occurs. 



Behavior 



Squid are generally sensitive laboratory animals, 

 responding very quickly with their sophisticated sen- 

 sory systems to any fast environmental change. 

 They habituate to many daily disturbances in the 

 tank system (e.g., tank cleaning, etc.) provided 

 everything is done slowly. Later in the life cycle they 

 become slightly less sensitive. 



Hatchlings were positively phototaxic and often 

 swam at the water surface. In nature, young squid 

 have been caught mainly by plankton nets mounted 

 on a sled and towed along the bottom (Recksiek and 

 Kashiwada 1979). It is not possible at this time to 

 explain the movements of hatchlings in nature based 

 upon laboratory observations of positive phototaxis. 



A key component in feeding behavior was move- 

 ment by the prey, regardless of the size or age of 

 the squid or food organisms. Young squid preferred 

 copepods but ate a variety and a very wide size 

 range of organisms (Fig. 4). In general, the squid 

 preferred crustaceans over fish, but the relatively 



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