™ 30 



A. 



■o- 



11 13 15 17 19 21 



Age (Days) 



n 



IT 



* 5 



O 



(5 



FISHERY BULLETIN: VOL. 87, NO. 3, 1989 



It 13 15 17 



Age (Days) 



a> 30 



z 



B. 



11 13 15 17 19 21 



Age (Days) 



* 



O 15 



11 13 15 17 19 



Age (Days) 



Figure 2. — Ingestion rates (A.); net assimilation efficiencies (B.); growth rates (C); and growth efficiencies (D.) of reared 

 walleye pollock larvae. Closed circles and open circles indicate well fed and poorly fed larvae, respectively. 



larvae caught at sea. In the laboratory, yolk-sac 

 larvae from days to 4 (posthatch) were growing 

 0.20 mm/d at 6.4°C. Growth rates decreased to 

 0.06 mm/d just after onset of feeding (4.8 mm 

 SL) and increased to 0.16 mm/d from days 19 to 

 21 (5.8 mm SL). Growth rates of field-collected 

 walleye pollock larvae, determined from otolith 

 increments, ranged from 0.12 to 0.25 mm/d, 

 linearized over ages 7-45 days (6.0-14.6 mm SL) 

 for larvae caught in the Gulf of Alaska in 1983 (at 

 5.5°-7.0°C (Kendall et al. 1987)). In 1987 the 

 growth rate of Gulf of Alaska walleye pollock 

 larvae at 5.8 mm SL was 0.18 mm/d as deter- 

 mined from the growth equation given in Yokla- 

 vich and Bailey (1989). Growth of field-caught 

 larvae, like laboratory-reared larvae, was slow 

 at ages corresponding to the transition from 

 endogenous to exogenous feeding. Specific 

 growth in dry weight was 7%/d. This is some- 

 what slower than the wet weight-specific gi-owth 

 rates estimated from field-caught larvae at 

 10%/d (Fukuchi 1976; Nishiyama 1981). These 

 weight-specific growth rates are much lower 

 than those of subtropical species (from 15 to 

 50%/d) (Houde and Schekter 1983; Theilacker 



1987), but they are similar to those of other sub- 

 ai'ctic species (Laurence 1975; 1978) 



Decreased evacuation rates with increased 

 larval size (and age) were closely related to the 

 development of the digestive system, especially 

 midgut coiling, which begins at about 5.2 mm SL 

 (13-16 days) and is completed at about 5.8 mm 

 (19-21 days). Our gut clearance times (5.3-6.1 

 hours) for first-feeding larvae fed rotifers are 

 similar to the 5 hours found by Paul (1983) for 

 pollock larvae fed copepod nauplii at 5.5°C. Gen- 

 erally these gut clearance times are considerably 

 slower than those of warm-water species, e.g., 

 northern anchovy at 1.15-1.5 hours (Theilacker 

 1987). Walleye pollock larvae with high ingestion 

 rates in high prey densities had faster rates of 

 gut clearance compared with those held in low 

 prey densities. Furthermore, larvae with full 

 guts placed in prey-free water had very slow 

 clearance rates, indicating that continuous feed- 

 ing facilitates movement of ingested prey 

 through the guts. 



Specific daily ration increased from 21 to 25% 

 at day 7 to a peak value of 46-51% at days 13-16 

 as a function of increasing ingestion rates. It 



532 



