EARLY LIFE HISTORY OF PACIFIC MACKEREL, SCOMBER JAPONICUS 



John R. Hunter and Carol A. Kimbrell^ 



ABSTRACT 



The early life history of Pacific mackerel, Scomber japonicus , is described from laboratory-rearing 

 studies and examination of stomach contents of sea-caught larvae. At 19° C mackerel eggs hatched in 

 56 hours, larvae were 3.1 mm standard length with a dry weight of 0.04 mg of which 50% was yolk. First 

 feeding occurred 46 hours after hatching; all larvae fed by 60 hours (age 2.5 days). Larvae were then 3.6 

 mm long with fully pigmented eyes and 10% of the yolk remaining. Starvation was irreversible if 

 larvae were not fed before age 4.5 days. Metamorphosis ( 15 mm standard length) occurred in 24 days at 

 16.8^ C to 16 days at 22.1° C. Larvae 3-5 days old consumed 87% oftheirbody weight per day and had a 

 mean gross growth efficiency in dry weight of 33%. Oxygen consumption was 6.1 m1 Qz per milligram 

 dry weight per hour at 18° C and 11.4 /xl O^ per milligram dry weight per hour at 22° C. Swimming 

 speeds ranged from 1.3 standard lengths per second for first-feeding \arvae to 3.8 standard lengths per 

 second for fish at metamorphosis. Fifty percent of the larvae were able to capture a prey when the width 

 of the prey was 85% of the width of the mouth and 95% were able to do so when the prey was 57% of the 

 width of the mouth. Cannibalism was common in rearing groups; at 8 mm standard length, 50% of the 

 larvae became capable of feeding on other fish larvae and cannibalism ceased when schooling com- 

 menced. Chief food items of sea-caught larvae were stages of copepods; maximum food width increased 

 rapidly with larval length and was equivalent to the maximum mouth width. Mean prey width was 

 38% of mouth width. The larger organisms, constituting half of the prey eaten, accounted for 85-90% of 

 the total voliune of food eaten. 



The development and distribution of eggs and lar- 

 vae of the western Pacific population of the Pacific 

 mackerel, Scomber japonicus , has been described 

 (Kramer 1960; Kramer and Smith 1970), but little 

 information exists on growth, behavior, and 

 physiology of the larval stages. Incubation times 

 and other data are known for the Japanese popula- 

 tion of S . japonicus (Watanabe 1970). This paper 

 provides some of the information needed to 

 characterize the early life history of Pacific mack- 

 erel, including incubation times, yolk absorption, 

 onset of feeding, vulnerability to starvation, 

 swimming and feeding behavior, food ration, and 

 oxygen consumption. 



METHODS 



Laboratory Experiments and Sea Samples 



Eggs were obtained from Pacific mackerel 

 maintained in spav^ming condition in the labora- 

 tory and induced to spawn by hormone injection 

 (Leong 1977). Effects of temperature on incubation 

 time were determined by placing test tubes con- 



'Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 

 92038. 



taining 10 eggs and 25 ml of seawater in a temper- 

 ature block set to produce a temperature gradient 

 of ll.l°-23.3°±0.2° C (2 SE (standard error)) 

 (Lasker 1964). Hatched eggs were counted at 2-4 h 

 intervals and time from fertilization to 50% hatch 

 estimated. Rate of yolk absorption was deter- 

 mined at 19.4°±0.4° C by measuring the surface 

 areas of the yolk-sac and oil droplet from tracings 

 made with an optical comparator (Wolfson 1965). 

 Six samples, each of 15-25, larvae were taken over 

 the first 72 h after hatching. 



To estimate the time of first feeding at 

 18.9°±0.3° C, groups of larvae without past feed- 

 ing experience were transferred to a 100 1 con- 

 tainer containing 150 rotifers/ml (Brachionus 

 plicatilus). Four hours later, they were removed 

 and the percentage of larvae that fed and the mean 

 number of rotifers in the gut were calculated. 

 Eight groups of 10-39 larvae were tested at periods 

 from 18 to 114 h after hatching. 



A starvation-based mortality curve was es- 

 tabilished at 19.0°±0.3° C by starting with 1,000 

 eggs in each of two 200 1 containers, and counting 

 and removing dead larvae daily. The age was de- 

 termined at which starvation became irreversible 

 in first-feeding larvae. Seven hundred and fifty 

 eggs were incubated in each of four 200 1 tanks and 

 the resulting larvae were fed for the first time at 



Manuscript accepted October 1979. 

 FISHERY BULLETIN: VOL. 78, N 



NO. 1, 1980. 



89 



