HURLEY: LOLIGO OPALESCENS RAISED IN THE LABORATORY 

 100. 



90- 



80 



70 



60 



50 



40- 



30 



20- 



10 



• • 



• • 



— I 1 



10 IB 



DAYS AFTER HATCHING 



25 



—I 

 30 



Figure 2. — Percent of attacks on Artemia nauplii which were 

 successful as a function of the age of the squid. 



(1970) found that for Sepioteuthis , the majority of 

 the prey were lost because the squid were unable 

 to judge the attack distance. In my experiments, 

 most unsuccessful attacks occurred because the 

 prey managed to escape after being initially 

 struck. Some of the variability in success rates 

 may have been due to different motivational 

 states of the squid. 



Feeding Rates 



Several methods were used to determine the 

 food ration of the developing squid. When the 

 squid fed on nauplii, feeding rates were deter- 

 mined at irregular intervals by choosing a squid 

 and watching it for 5 min to determine the 

 number oi^ Artemia nauplii consumed during this 

 period. All of the observations accumulated dur- 

 ing a given week were combined. For each week, I 

 calculated the food eaten over a 24-h and 18-h 

 feeding period. The squid captured prey when the 



Table l. — Estimated feeding rates (percent body weight eaten 

 {)er day) of squid in rearing tanks. Each value is average for all 

 values for a given week. Values through week 4 are based upon 

 observed short-term feeding rates on Artemia nauplii and are 

 given for assumed 18- and 24-h feeding periods. Subsequent 

 values are based on counts of Artemia adults consumed in tanks 

 1 and 2. 



overhead lights were off, but it was not possible to 

 establish how much was eaten. When adult Ar- 

 temia was the primary source of nourishment, 

 record was kept of the approximate number of 

 food organisms introduced to the tank and their 

 average weight. There is some error introduced 

 here because some of the brine shrimp died and 

 were not consumed. The average weight of the 

 squid during each week was obtained from the 

 growth data and length-weight relationships pre- 

 sented in the next section. Average weight of 

 Artemia adults was 0.3 mg (obtained from six 

 random samples of 10 to 20 individuals each) and 

 average weight of nauplii was 0.002 mg (John R. 

 Hunter pers. commun.). Food consumption is 

 shown in Table 1. 



One short-term experiment was performed to 

 examine the feeding rate of 36-day-old squid on 

 yolk-sac larval anchovies. Five squid were placed 

 with 100 anchovy larvae in 8 liters of water and 

 were left for 285 min. At the end of this period 58 

 larvae had been eaten. This gives a feeding rate 

 of 2.4 larvae/squid • hour Theilacker and Lasker 

 (1974) gave the average weight of a larva of this 

 size as 0.022 mg. Using this information and the 

 average weight of the squid, a feeding rate of 

 0.028 mg anchovy/mg squid h is obtained. 



Growth 



Since the number of squid being reared was 

 small, specimens were not sacrificed for growth 

 measurements alone. Every time a squid died, it 

 was immediately measured. These measure- 

 ments constitute the majority of the points on the 

 growth curve shown in Figure 3. The points indi- 

 cated by the x's are measurements which were 

 made on squid that had been selected while alive 



179 



