FISHERY BULLETIN: VOL. 84, NO. 4 



took place mainly at night, but some individuals 

 spawned during the day. Egg capsules in the early 

 portion of the spawning period were small, with a 

 length of 2.2 to 4.7 cm when laid. Superficially there 

 were no differences with normal capsules, but usual- 

 ly the early ones contained only a few eggs while 

 a few had none. Typical newly laid egg capsules 

 were between 6.0 and 9.0 cm and contained an 

 average of 156 eggs (range 107-199). These egg cap- 

 sules were normal in length and egg number com- 

 pared with L. opalescens in nature (Hixon 1983). 



A large number of typical egg capsules were in- 

 cubated and a normal second generation hatched. 

 The average mantle length of second generation 

 hatchlings was 2.3 mm ML (range 1.9-2.7 mm ML, 

 n = 13). This was smaller compared with first 

 generation hatchlings (average 2.7 mm ML) but 

 there was no difficulty in rearing them on copepods 

 for 10 d. Since initial survival was confirmed, fur- 

 ther rearing ceased. 



In L.O. 1982, three patches of artificial egg cap- 

 sules made of silicon glue were placed on the bot- 

 tom of the RW tank to stimulate spawning. The 

 squid spawned 15 fertilized egg capsules around the 

 artificial capsules (Fig. 16). 



DISCUSSION 



Water Quality and System Design 



Water quality was consistently good throughout 

 both experiments and was probably a major con- 

 tributor to culture success. The CT systems were 

 particularly clean (Fig. 2) because the water volume 

 was relatively large for the small biomass of animals. 

 In the large RW system, water quality changed only 

 slightly when the biomass of squid and food or- 

 ganisms reached its maximum from approximately 

 days 150 to 220 (Figs. 2, 5, 7). The highest total 

 biomass level was 1,706 g between days 180 and 190 

 in L.O. 1981, which is equivalent to approximately 

 155 g/m 3 of water. At this point, the nitrate- 

 nitrogen level reached 23 mg/L, which is still low 

 [Spotte (1979a) gave a conservative safe level of 20 

 mg/L for most marine organisms]. Ammonia-nitro- 

 gen and nitrite-nitrogen levels always stayed below 

 the recommended safe level of 0.1 mg/L (Spotte 

 1979a) in both experiments. We know from our re- 

 cent unpublished data that a drop in pH (which ac- 

 companies nitrogen level increase; Hirayama 1966) 

 is more dangerous to squid; therefore, addition of 

 sodium bicarbonate was necessary to keep the pH 

 near 8.0. Several improvements in system design 

 helped improve water quality over our L. opalescens 



experiment in 1980 (Yang et al. 1983a), when nitrite- 

 nitrogen reached 1.22 mg/L and nitrate-nitrogen 

 reached 39.20 mg/L. These included increased 

 culture water depth and volume in the RW (5,990 

 to 8,610 L), increased number of protein skimmers 

 from 2 to 5 and generally more oyster shell substrate 

 area for increased biological filtration. Furthermore, 

 regular addition of trace metals assured high levels 

 since losses occur through foam fractionation in pro- 

 tein skimmers (Spotte 1979b) and metabolism of 

 filter bed bacteria, squid, and food organisms. 



Growth and Survival 



Growth in L. opalescens is very fast (Figs. 8, 9) 

 and conforms to a general trend among cephalopods 

 in which the early life cycle is characterized by rapid 

 exponential growth, followed by slower logarithmic 

 growth until reproduction and death (Boyle 1983; 

 Forsythe and Van Heukelem in press). 



Egg development is temperature-dependent and 

 takes 19 to 25 d at 16.5°C (Fields 1965), 27 to 30 

 d at 15°C (L.O. 1981, this report) and 30 to 35 d 

 at 13.6°C (McGowan 1954). Hatching success was 

 high, and young squid survived several days on in- 

 ternal yolk. Many squid will feed before internal yolk 

 is absorbed (Boletzky 1975). The young will feed on 

 a variety and wide size range of crustaceans and 

 fishes (Fig. 4). Zooplankton, but especially copepods, 

 are readily attacked and eaten by very young squid. 

 It is noteworthy that relatively large mysids could 

 be fed successfully to hatchlings within the first 

 week (Fig. 3: L.O. 1982) and for 3 to 4 mo there- 

 after as a primary food. Mysids are easier to col- 

 lect and acclimate to laboratory conditions and are 

 thus attractive to the culturist for pragmatic 

 reasons. Loligo opalescens hatchlings (2.3-2.8 mm 

 ML) are much larger than those of L. pealei (1.7 mm 

 ML) or L. plei (1.6 mm ML) (McConathy et al. 1980) 

 and are consequently easier to rear because larger 

 food organisms can be used immediately. Larval fish 

 were attractive to young squid but are difficult to 

 provide. 



Major mortality occurred within 10 d posthatch- 

 ing. Although high food densities and variety were 

 provided (Tables 1,2; Figs. 3, 4, 5), many squid ap- 

 peared to have difficulty making the transition from 

 passive yolk absorption to active feeding on live 

 organisms. A learning process may be involved, 

 because capturing copepods was initially difficult 

 (squid have been observed to miss 40 times con- 

 secutively) and improved when squid attacked from 

 behind. Past experience (cf., Yang et al., 1983a) sug- 

 gested that increasing food abundance relative to 



790 



