YANG ET AL.: CULTURE EXPERIMENTS OF LOLIGO OPALESCENS 



differed, since distal embryos usually hatched first. 

 Since we used early stage eggs removed from their 

 habitat in California, no polychaete worms (Capitella 

 ovincola) were observed in the egg capsules (cf., 

 McGowan 1954), although we had observed worms 

 in other late stage California egg capsules. 



During embryonic development, granules or 

 crystals appeared in the perivitelline fluid of some 

 eggs, but no significance to survival or development 

 could be associated with this condition. The outer 

 tunics of the egg capsules incubated in Instant 

 Ocean were more elastic until the later stages 

 (around stage 27) than those incubated in natural 

 seawater. More bacteria and other benthic or- 

 ganisms grow on the capsules incubated in natural 

 seawater. These differences did not influence devel- 

 opment or hatching success. Embryos near hatch- 

 ing (stage 29) generally moved little or were nearly 

 static, but in most individuals the external yolk sac 

 was already broken off within the egg. External yolk 

 sacs were observed on a few hatchlings. In L.O. 

 1981, bright illumination stimulated hatching in very 

 late stage eggs and therefore light levels were in- 

 creased during later stages of egg development in 

 L.O. 1982. 



Foods and Feeding 



The species and size of food organisms were 

 similar in the two experiments. The general progres- 

 sion of food types began with zooplankton, then 

 mysidean shrimps, then palaemonid shrimp larvae 

 and adults, and finally fishes (Fig. 3). The use of 

 brine shrimp has been curtailed since they were 

 found to be unattractive to the hatchlings. 



The size range of food organisms fed in the first 

 30 d is large, especially when compared with the size 

 of 1-d-old hatchlings (2.3-2.8 mm ML, Fig. 4). How- 

 ever, as shown in Figure 4, the hatchlings have only 

 small fins and are not strong swimmers; therefore, 

 feeding on active prey at this stage is not excellent. 

 A summary of the types and quantities of food of- 

 fered in the experiments (L.O. 1981 is used as an 



example) is given in Figure 5. Large amounts of food 

 were available to the squid; this was important dur- 

 ing the first weeks when hatchlings could only cap- 

 ture food organisms drifting very close to them. The 

 relationship of hatchling to food organism density 

 during the first 59-d period in each experiment is 

 summarized in Table 1. Unfortunately there was no 

 clear relationship between densities and survival. 

 For example, in L.O. 1982, there were twice as 

 many food organisms per squid as in L.O. 1981, but 

 survival (cf., Fig. 13) was not better. Figure 5 shows 

 more specifically the number of food organisms fed 

 daily in L.O. 1981. 



The early rearing period in L.O. 1981 and 1982 

 coincided with the spawning of mysid shrimp in the 

 Galveston estuaries. Therefore, small mysids with 

 a total length of about 2.0 mm (Fig. 4B) were abun- 

 dantly supplied. This was particularly important 

 since small mysids swim more frequently in the 

 water column than do adults. Young mysid hatch- 

 lings were given as food by day 12 in L.O. 1981 and 

 immediately in L.O. 1982 (Fig. 3). Small mysids 

 distribute themselves more evenly in the culture 

 tanks and are easier for hatchlings to capture. 

 Palaemonetes spp. were fed to juvenile and adult 

 squid (Fig. 3). Shrimp ranged in size from 2.0 to 25.0 

 mm. They were graded by size and fed based on size 

 and availability. Daily siphoned remains indicated 

 that only the abdominal flesh was consumed, with 

 the thorax and carapace discarded. 



Fish were generally used for juvenile or older 

 squid. However, fertilized red drum eggs were 

 available in L.O. 1981, and larvae up to 13-d old (Fig. 

 4E) were given to the hatchlings. In the two ex- 

 periments, a total of over 14 fish species of 10 

 families were fed (Table 2). To determine the diet 

 preference for fish species, the actual consumption 

 of fish (i.e., total weight of fish put in tank minus 

 total weight of fish remains) was compared for a 

 total of 5 kg fish fed in L.O. 1982 (Fig. 6). The 

 cyprinodont fish were most preferred (consumption 

 of 83%). Only small Fundulus spp., smaller than 31 

 mm (Cyprinidontidae), were fed because large Fun- 



Table 1.— The mean density of squid and food organisms per liter of culture water from days 



0-30 and 30-59. 



775 



