HUNTER and KIMBRELL: EARLY LIFE mSTORY OF PACIFIC MACKEREL 



005- 



LnW = -5 442-0 337 T 

 r^ =0 970 



e 



OD 



I 



^ 0005 - 



2 

 < 

 liJ 



5 



001 - 



.000 



2 3 4 5 



ELAPSED TIME (h) 



FIGURE 10.— Rate of gastric evacuation of 4.01+0.03 mm SL 

 Pacific mackerel larvae fed Brachionus plicatilis. Each point 

 represents the mean dry weight of fi. plicatilis in guts of 13-16 

 larvae. Dry weight estimated by counting numbers of B. 

 plicatilis in stomachs and multiplying by the mean dry weight of 

 one B. plicatilis iO.lSfig) iTheilacker and McMaster 1971). 



Warburg flasks was probably less than that of 

 free-swimming larvae. These respiration mea- 

 surements do establish a lower limit to food ration, 

 because the ration would have to exceed the 

 metabolic requirement just to meet maintenance 

 costs. 



DISCUSSION 



The characteristics of the embryonic period (du- 

 ration of incubation and yolk-sac periods, extent of 

 yolk reserves, size at first feeding, and ability to 

 withstand starvation) were similar to other tem- 

 perate fishes with small pelagic eggs (Lasker et al. 

 1970; Zweifel and Lasker 1976) and did not differ 

 greatly from some subtropical species (Houde 

 1974). Small differences in these characteristics 

 may be of importance (Houde 1974) but growth, 

 metabolism, feeding, and swimming behavior are 

 of more value in characterizing the early life his- 

 tory of Pacific mackerel. 



Pacific mackerel larvae grew rapidly, complet- 

 ing metamorphosis (15 mm SL) in 2-3 wk. Fast 

 growth appears to be characteristic of scombroid 

 larvae and is even more rapid in tropical scom- 

 broids: Auxis thazard grew to 64 mm SL in 17 d 

 (Harada, Murata, and Furutani 1973) and A. 

 tapeinosoma grew to 49 mm SL in 18 d (Harada, 

 Murata, and Miyashita 1973). Fast growth re- 

 quires a large food ration; we found that Pacific 

 mackerel larvae consumed about 877f of their dry 



Table 3. — Estimate of ration, metabolism, and growth efficiency of 3-5 d old Pacific mackerel larvae fed Brachionus plicatilis. 



'Calculated from mean larval length using relation given in Figure 4. 



Mean counts of 8. plicatilis in stomach converted to weight using one B. plicatilis = 0.16 ^g (Theilacker and McMaster 1971). 

 Each sample consisted of 13-16 larvae; sampling began after first hour of feeding. 



Ration = (/•■/(• f) - r, where r is mean stomach contents, k is rate of gastric evacuation (0.377), and t is duration of feeding period (12 h). (From G. Stauffer, 

 unpubl. manuscr. Southwest Fisheries Center. La Jolla. Calif ) 



Caloric value of B. plicatilis = 5.335 cal/g (Theilacker and McMaster 1971). 



Maintenance requirement from; 7.45 /nl 02,mg per h; 1 ^1 O2 = 0.005 cal; time = 24 h; and dry weight of larvae on day ration estimated. 



Caloric value of weight gained assumed to equal 5.000 cal/g. 



Gross efficiency (dry weight) = weight gam/ration. 



99 



