FISHERY BULLETIN: VOL. 82, NO. 1 



Juveniles were then subdivided and transferred to 

 different regimes, allowing an examination of the 

 interactive influence of greater age and novel 

 environment on increment production. 



MATERIALS AND METHODS 



Fertilized Porichthys eggs were collected inter- 

 tidally from White Rock, British Columbia, on 9 and 

 22 June 1982. Yolk-sac larvae remain attached to the 

 rock upon which the eggs were originally deposited 

 (Arora 1948), necessitating the collection of both 

 rocks and egg masses. Upon return to the laboratory, 

 eight separate egg masses (50-250 ova each) were 

 isolated in individual saltwater aquaria and main- 

 tained under a diel photoperiod and a temperature of 

 13°C. Small amounts of methylene blue, strep- 

 tomycin sulphate, and penicillin G were used to con- 

 trol bacterial and fungal infection. Embryo 

 development varied both among and within egg 

 masses, but the difference appeared to be <2-3 d. 



On 1 July, egg masses were exposed to an 

 experimental environment. Environmental regimes 

 were selected to provide a diel periodicity of either 

 photoperiod or temperature. A third regime main- 

 tained constant conditions of both variables. In this 

 manner, the influence of both factors on increment 

 formation could be determined for newly hatched lar- 

 vae. Daily increment production in the constant 

 environment would suggest the presence of an 

 endogenous circadian rhythm. Regimes were as 

 follows: 



14L:10D at a constant temperature of 19°C 



(14L:10D/CT) 

 24L with 14 h at 21 C C and 10 h at 19 C (24L/ 



14TV10T,) 

 24L at a constant temperature of 19°C (24L/ 



CT) 



Duplicate aquaria, each containing an egg mass (or 2 

 small masses, if at similar developmental stages), 

 were kept in light-proof, temperature-controlled 

 cubicles under each of the above environments. All 

 lighting was fluorescent (30 jiiEs/m 2 /s). Temperature 

 fluctuations were timer-controlled and conducted 

 parallel to the light cycle. New temperatures were 

 reached VA h after initiation. Mean temperatures 

 approximated those of the egg collection site; diel 

 temperature fluctuations were present at the site, 

 but were not recorded. Aquarium water was changed 

 at 7-10 d intervals. Hatching date varied among and 

 within egg masses, beginning between 7 and 1 1 July. 

 Release from the rock (before completion of yolk-sac 



resorption) was more variable, and occurred between 

 23 July and 9 August. Live adult Artemia were first 

 provided as food on 30 July and were consumed by 

 both released and attached larvae. Thereafter, 

 Artemia were maintained in all aquaria at all times, 

 with the exception of two 3-d periods when food was 

 not available. Food abundance did not differ among 

 the aquaria. Observations of feeding fish indicated 

 that the accessibility of Artemia did not limit 

 growth. 



By 10 August, all fish were about 32-d old 

 (posthatch) and had become juveniles (i.e., had 

 assumed the appearance of an adult). To test the 

 effect of an altered photoperiod or temperature cycle 

 on juveniles, one tank from each of the environmental 

 regimes was subdivided (Fig. 1). About 25 fish were 

 transferred from one aquarium ("cohort") to each of 

 the remaining environments, while leaving 25 fish in 

 the original environment as a control. Sagittae were 

 removed from up to 25 of the excess fish to determine 

 the effect of the original environment on newly 

 hatched larvae. In order to remove any intercohort 

 variability of hatching dates, only one of the two avail- 

 able cohorts from each environment was subdivided 

 and sampled. However, low numbers of 1 4L: 1 0D/CT 

 fish necessitated the transfer of an entire cohort. 



For processing, the sagittae were brushed free of 

 tissue and glued sulcus-side up with instant glue on a 

 standard microscope slide. Sagittae were ground and 

 polished with metallurgical lapping film (grit size 30 



AUG 10 

 JULY 1- AUG 10 TRANSFER 



14L 10D/CT 



24L/ 14T, 10T 



24L/CT 



AUG 10- SEPT 10 



24L/14T, 10T 2 141 10D/CT 24L/CT 



Fk;i RE 1. — Summary of experimental environmental regimes of 

 plainfin midshipman through time. Fish transferred to new environ- 

 ments on 1(1 August came from the same egg mass as that sampled 

 on 10 August. 



166 



