4.00 mm. long was 39.5 percent, 17.8 percent 

 at 5.00 mm., 6.7 percent at 6.75 mm., and Z.9 

 percent at 7.75 mm. The rapid decrease in 

 abundance after 7.5 mm. is assumed to be 

 masked by the ability of the larvae to escape 

 capture by swimming away from the mouth of 

 the collecting net. 



3.23 Adolescent phase 



In 1966 several hundred Pacific mackerel 

 were hatched from eggs and reared to preadult 

 stages at the Fishery-Oceanography Center. 

 At about age 2 months several in this batch 

 were accidentally killed in their tank. Eight of 

 these were X-rayed and measured; their 

 lengths ranged from 35 to 77 mm. 



Nothing is known about juvenile Pacific 

 mackerel in the sea. Their behavior in aquar- 

 ium tanks indicates that they are particulate 

 feeders on live or "dead" animal food- -even 

 prepared food--taking live or frozen brine 

 shrimp, cut bait, fish or squid, and prepared 

 trout food. The last was the least digestible; 

 undigested material was voided shortly after 

 feeding. 



3.3 Adult phase 



3.31 Longevity 



Most of the fish taken commercially are less 

 than 6 years old; most are 0, 1, 2 and 3 years 

 old. Occasionally large mackerel appear in the 

 catch. Fitch (1952) reported that the oldest 

 Pacific mackerel aged was 11 years. Fitch 

 (1956) reported that fish over 8 years old were 

 rare and that 6-year-olds were becoming very 

 uncommon. 



3.32 Hardiness 



No data on hardiness in ocean environment. 

 Mackerel held in aquaria do best in circular 

 plastic -lined tanks. 



3.33 Competitors 



No data except that since they are often 

 caught with jack mackerel, they may connpete 

 with that species. 



3.34 Predators 



Not studied except for predation by man. 



3.35 Parasites, diseases, injuries 

 and abnormalities 



No data for fish in ocean environment. In 

 captivity these fish eventually develop hyper- 

 plasia (cancer-like growths) on the skin in the 

 head region. 



3.4 Nutrition and growth 



3.41 Feeding 



Pacific mackerel feed at any time of day. 

 They can be caught at night by chumming 

 under lights. They are particulate feeders. 



3.42 Food 



Fry (1936b) stated that this mackerel has a 

 tremendous appetite and shows very little dis - 

 c rimination inits feeding. Any animal matter 

 alive or dead is acceptable for food. He re- 

 ported that the fish takes fish or squid several 

 inches long, as well as small animals such as 

 cope pods or other free -swimming crustaceans. 

 He stated that in general they feed on one kind 

 of food at a time--for example, copepods, 

 anchovies, or squid, but not mixtures ofthese, 

 (See 3.23 for feeding in aquaria.) 



3.43 Growth rate 



When 2 years old. Pacific mackerel are about 

 12 inches (305 mm.) long and weigh about 3/4 

 pound (340)--Fitch, 1951. The relation of 

 weight, length, and age are shown in figure 7. 



Fry (1936b) listed the following approximate 

 weights and lengths (in ounces and inches) 

 and called them "rough averages": 



Condition factors (table 3) were derived from 

 data for 137 mackerel presented by Fitch 

 (1951, table 14) and from the data of G. O. 

 Schumann (unpublished) on 139 of 340 macke- 

 rel hatched and reared at this laboratory, 



A- ^ n, <• 1 i^- weight X 10? 

 according to the formula: K fork length ' 



where weight is in grams and length is in 

 nnillimeter s. 



Hatanaka and Takahashi (1956) captured and 

 held in captivity, for feeding experiments, a 

 number of Japanese mackerel for which I 

 calculated the condition factors. The factors 

 for their specimens, when caught, were higher 

 than the ocean specimens of comparable sizes 

 shown in table 3. 



3.44 Metabolism 



No data. 



