BAILEY: EARLY LIFE HISTORY OF PACIFIC HAKE 



vival. Hunter (1980) contrasted several types of 

 life history tactics for larvae of marine fishes. He 

 indicated that in relatively cold water, where 

 metabolic costs are low, a tactic of slow growth, 

 feeding on large prey, and passive hunting may 

 be common. This does appear to be the strategy 

 of Pacific hake larvae. This tactic is quite differ- 

 ent from that of high metabolism, fast growth, 

 and active hunting demonstrated by other lar- 

 vae, such as Pacific mackerel and to a lesser ex- 

 tent northern anchovy. Larvae of Pacific hake 

 are located in colder water than larvae of Pacific 

 mackerel and northern anchovy (Ahlstrom 1959) 

 and compared with these other species the 

 growth of Pacific hake larvae is slow (Fig. 9). 

 Metabolic rates are difficult to compare because 

 of different experimental techniques, but as a 

 lower limit (due to the restrictive container size), 

 3-5 d old Pacific mackerel larvae require about 

 0.411 Ml-0 2 /animal per h at 19°C (Hunter and 

 Kimbrell 1980). This compares with 0.265 M l-0 2 / 

 animal per h for first-feeding Pacific hake larvae 

 at 12°C from this study. 



I have calculated the energetic requirements 

 of a first-feeding Pacific hake larva based on the 

 routine metabolic rate at 12°C (the ambient tem- 

 perature off the California coast) and growth in 

 weight for larvae caught in the field, after cor- 

 recting for preservation effects (Table 5). These 

 values were converted to calories assuming val- 

 ues of 1 /j1-0 2 =0.005 cal and 1 mg-dry weight of 



TABLE 5.— Caloric requirement of first-feeding Pacific hake 

 larvae from growth and metabolism. 



Mackerel 



Anchovy 



Hake 



Figure 9.— Comparative growth of field-caught Pacific hake 

 larvae (at 11°-14°C; this study), field-caught anchovy larvae 

 (13°-16°C; Methot and Kramer 1979), and laboratory-reared 

 Pacific mackerel larvae (19°-20°C; Hunter and Kimbrell 

 1980). 



Respiration rate at 12°C - 30 /yl/animal per h 



Length Weight Corrected 



(mm) (mg) weight (mg)' 



Growth day 4 3 412 0440 0.0694 



day 5 3 577 0.0512 0.0808 



Weight gain 011 mg/d = 0550 calories 2 

 Respiration = 7.20 /j\/d = 0.0360 calories 3 



00910 calories 



Daily ration = Metabolism f Growth t Nonassimilated + Egestion 

 Daily ration x 0.7 = Metabolism + Growth 

 Daily ration = 130 calories 



'Corrected for preservation effects. 



2 5 003 cal/mg-dry wt tissue (Laurence 1977). 



3 005 cal//jl-Q 2 (Laurence 1977). 



larval fish tissue = 5.003 cal (Laurence 1977). 

 The average first-feeding hake larva thus re- 

 quires 0.091 cal/d to maintain and grow. This 

 value is likely to be an underestimate of the cal- 

 oric requirement due to an undetermined 

 amount of energy needed to attack, capture, and 

 digest prey animals. Estimates of assimilation 

 coefficients range from 0.8 (Healy 1972; Dagg 

 1976) to 0.5 ( Vlymen 1977). Assuming an assimi- 

 lation coefficient of 0.7, as suggested by Ware 

 (1975) and Laurence (1977), Pacific hake larvae 

 would need to ingest 0.130 cal/d to satisfy meta- 

 bolic and growth costs. Although this seems to be 

 a reasonable estimate, significant errors may 

 arise from the factors used for length-weight 

 conversion, preservation effects, and from the 

 assumed assimilation coefficient. I would sug- 

 gest a more thorough examination of these fac- 

 tors in future experiments. 



Using Sumida and Moser's( 1980) report on the 

 stomach contents of 3-4 mm Pacific hake larvae 

 (Table 6), I calculated an estimate of daily ration 

 that can be compared with the above estimate. 

 Several approximations are necessary in this 

 calculation, including 1) a feeding period of 12 h, 

 2) a digestion time, which I assume to be 5 h— 

 ranges for other species are 3-8 h for herring 

 (Werner and Blaxter 1980) and 2-4 h for Pacific 

 mackerel (Hunter and Kimbrell 1980), and 3) a 

 value of 5.2519 cal/mg-dry wt for copepods 

 (Laurence 1976). The daily ration can then be 

 calculated as: Daily ration = Stomach content 

 weight X Feeding period/Digestion time (Feign- 

 baum 1979; Laurence 1977). For small Pacific 

 hake larvae the daily ration thus calculated is 

 0.129 cal, which compares very closely with the 

 previous estimate. 



Hunter and Kimbrell (1980) calculated that 

 3-5 d old Pacific mackerel larvae require 0.143 

 cal/d to maintain and grow, based on the weight 



595 



