HURLEY: LOLIGO OPALESCENS RAISED IN THE LABORATORY 



During the first 4 wk the squid (groups 1 

 through 3) were fed newly hatched brine shrimp, 

 Artemia salina, nauplii which were kept at densi- 

 ties ranging from 1 to 20 nauplii/ml. After this 

 time, small adult brine shrimp were added (aver- 

 age length 5.4 mm; range 2.5 to 8.0 mm) and were 

 the major source of nourishment for the remainder 

 of the rearing period. In groups 4 and 5, small 

 adult Artemm as well as nauplii were used as food 

 during the first 4 wk. 



Squid were measured using an optical microm- 

 eter on a dissecting microscope. Measurements 

 are of dorsal mantle length (measured dorsally 

 from the tip of the tail to the farthest anter- 

 ior point on the mantle). Mantle length is less 

 variable than a measurement of total length, 

 which depends upon the degree of stretch of the 

 arms and tentacles. To make possible conversions 

 to total length, measurements were made of both 

 dorsal mantle length (ML) and total length (to 

 tips of arms, not tentacles) (TL) on 35 juvenile 

 animals, and the average ratio ML/TL was 0.62 

 ± 0.014 ( ±2 SE). Measurements are all on freshly 

 dead unpreserved animals. For weight measure- 

 ments, squid were rinsed in distilled water and 

 oven dried at 60°C to a constant weight. 



Respiration measurements were made using a 

 Warburg constant volume respirometer with 

 respiration vessels kept at constant temperature 

 in a water bath. The respiration vessels contained 

 from 2 to 30 squid and were kept in constant mo- 

 tion by gentle shaking. 



Estimates were made of the number of squid 

 surviving at intervals throughout the study. The 

 number of squid alive on any day was the average 

 of three counts taken of live animals in the tank. 



Daily observations were made of the feeding 

 behavior of the squid. At various times through- 

 out the day, a squid was selected and observed for 

 about 5 min. The number of feeding attempts and 

 successful captures of prey were recorded. 



RESULTS 



Survival 



Mortality in all of the tanks was initially high 

 (Figure 1). This is similar to what LaRoe (1971) 

 found in rearing Sepioteuthis sepioidea. LaRoe 

 speculated that the high initial mortality was due 

 to insufficient quantities of food. This probably 

 was not the case in my studies, as a large amount 



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80 



70 



^ 60 



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ff 50 



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30- 



20- 



10 



D GROUP I 

 A GROUP 2 

 O GROUP 3 



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10 



20 



30 40 



50 

 DAYS 



60 



70 



80 



90 



100 



Figure l. — Estimated percent survival of Loligo opalescens in 

 the rearing tanks. Group 1 started with 300 squid; group 2, with 

 300 squid; and group 3, with 250 squid. 



of food was continually available at this stage. 

 Some of this mortality could have been caused by 

 squid which did not initiate feeding. Fields (1965) 

 found that L. opalescens which did not appear to 

 be feeding lived up to 10 days and still had some 

 internal yolk reserves left at the end of this time. 

 From 30 to 60 days mortality was low, but after 

 60 to 70 days mortality again increased. It is pos- 

 sible that the brine shrimp did not provide an 

 adequate diet for squid older than 60 days. 



Feeding Behavior 



Attack 



The attack of a young L. opalescens is similar to 

 that described for adult Loligo (Fields 1965), 

 Sepioteuthis (LaRoe 1970), and Sepia (Messenger 

 1968). Messenger divided the Sepia attack into 

 three motor patterns: attention, positioning, and 

 seizure. These three patterns may also be used to 

 describe the attack of yoimg L. opalescens. Dur- 

 ing attention, the squid orients toward a particu- 

 lar prey. The arms and tentacles are extended in 

 front of the squid and form a tight cone which is 

 pointed toward the prey. Color changes such as 

 those noted for Sepioteuthis (LaRoe 1970) and 

 Sepia (Messenger 1968) were not observed. 



177 



