FISHERY BULLETIN: VOL. 82, NO. 1 



end of the experiment, and the 1980C group was 

 starved from hatch to death. The 1980D group was 

 reared at 7°C for 3 d, before it was accidentally de- 

 stroyed. A fourth group, 1980B, was formed from a 

 1980A subsample and was placed in its own 50 1 

 aquarium after 7 d of feeding and then starved for 

 5d. 



Two groups, 1981A and 1981B, were reared in 

 April-May of 1981 at the Bamfield Marine Station, 

 Bamfield, B.C. The eggs came from spawn laid on 

 Fucus spp. in the intertidal zone of Toquart Bay, 

 Barkley Sound, B.C. Therefore, the eggs came from 

 the lower west coast stock. The first population, 

 1981 A, was raised in a 1,000 1 circular, flow-through 

 aquarium. The water temperature rose gradually 

 from 8° to 9°C over the rearing period. Food was 

 added daily. Group 1981B was reared in a culture 

 chamber suspended in Bamfield Inlet. The chamber, 

 a 2,000 1 circular tank (Marliave 1981), floated at the 

 surface of the Inlet. Wild plankton was swept through 

 louvres on one side of the chamber by tidal currents 

 and was trapped in the chamber where it served as 

 food for the larvae. During the first 3 wk , no herring 

 larvae was in the plankton from the Bamfield Inlet, so 

 the tank population was not contaminated with wild 

 herring. The surface water temperature of the Inlet 

 over the rearing season was 9°-10°C. 



One group, 1982 A, was reared from eggs in the 

 laboratory at the Bamfield Marine Station, April- 

 May 1982. The group grew in a 25 1 rectangular 

 aquaria cooled to 8°-9°C. The eggs came from spawn 

 laid on eelgrass, Zostera marinus, in the intertidal 

 zone at the head of Bamfield Inlet and, therefore, 

 came from the lower west coast stock. The fish were 

 fed from hatch to age 30 d, and then the survivors 

 were moved to another tank of the same size where 

 they were starved for 8 d. This subgroup was 

 named 1982B. 



The lighting for all the laboratory groups was 

 fluorescent and was on a 10-h light: 14-h dark cycle. 

 This cycle was cued to the natural photoperiod with 

 light sensors. Water in all of the tanks, except 1981A 

 and 1981B, was gently aerated with an airstone, and 

 about one-third of the volume was replaced daily with 

 fresh seawater. Dead organisms and feces were daily 

 siphoned off the floor in all tanks, except 198 IB 

 which did not accumulate wastes because its floor, 

 drilled with over 1,000 small holes, was self-cleaning. 



Hatching 



All larvae in any single group were hatched within 

 24 h of each other. In 1980, hatching was stimulated 

 by scraping the eggs off the wall of a holding tank. In 



1981 and 1982, hatching was stimulated by exposing 

 late-stage eggs to air for 1 5 min. The exposure caused 

 an explosive hatch when the eggs were returned to 

 seawater. The egg masses were removed from the 

 tanks <24 h after hatching began. 



Food 



Food for three of the four fed populations consisted 

 of freshly hatchedArtemia nauplii. One of the feeding 

 groups, 1981B, fed exclusively on wild plankton 

 swept into the chamber by tidal currents. Another 

 group, 1 98 1 A, was raised on a diet of Artemia nauplii 

 supplemented with wild plankton captured with a 

 plankton net from the surface of Bamfield Inlet, In all 

 feeding groups, food was first supplied either at 

 hatch or before the second day after hatch, the day 

 when Pacific herring larvae first begin to exhibit feed- 

 ing behavior. Both the Artemia nauplii and the wild 

 zooplankters were attracted to the overhead light, 

 and they tended to cluster in a patch at the surface of 

 the water. Enough food organisms were added each 

 day to the feeding groups to maintain the patches at 

 all times so that the larvae of these groups had the 

 opportunity to feed at will at any time. It is not known 

 whether the 198 IB larvae in the culture chamber had 

 a similar opportunity, but the relatively high growth 

 rate of this group indicates that food was 

 abundant. 



Absence of food organisms in the water of starving 

 groups was ensured by filtering seawater through a 

 layer of glass wool before it was added to a tank. Sam- 

 ples of filtered water were examined under a micro- 

 scope to verify the absence of food organisms. 



Samples 



Samples of 10-18 larvae were taken from each of the 

 groups at intervals of 2-20 d. In 1980 the fish were 

 frozen at -10°C, and in 1981 and 1982 they were 

 preserved in 377c isopropyl alcohol. The standard 

 length was measured from the tip of the snout to the 

 end of the notochord with the vernier scale of a com- 

 pound microscope. Some of the larvae were 

 measured live before preservation, stored in- 

 dividually, and then measured again 1-6 mo later. 

 Freezing caused a mean (±1 SD) percent shrinkage 

 of 6.3 + 3.5 (n = 26), and isopropyl alcohol caused a 

 mean (± 1 SD) percent shrinkage of 0.04 ± 3.2 (n = 

 97) which was not significantly different from 0% 

 shrinkage (t = 0.0124, df = 96, P > 0.9). An examina- 

 tion of the individual percent shrinkages showed no 

 trend with live standard length. Frozen lengths were 

 corrected to live lengths by multiplying by the factor 



114 



