MATURATION AND INDUCED SPAWNING OF 

 CAPTIVE PACIFIC MACKEREL, SCOMBER JAPONICUS 



Roderick Leong 1 



ABSTRACT 



Pacific mackerel, Scomber japonicus, became sexually mature under laboratory conditions and were 

 induced to spawn with hormone injections. Fish caught before the major spawning season became 

 mature under the natural photoperiod and under artificial photoperiods of 4 h light 20 h dark, 8 h light 

 16 h dark, and 16 h light 8 h dark. Mackerel caught near the end of the spawning season redeveloped 

 their gonads more rapidly at 18°C than at 15°C or ambient temperature. A 16°C-14 h light 10 h dark 

 environment was effective in maintaining mackerel in spawning condition beyond the normal spawn- 

 ing season. Any of three combinations of hormones induced spawning: gonadotropin from ground 

 salmon pituitary followed 24 h later by gonadotropin from pregnant mare serum; human chorionic 

 gonadotropin followed 24 h later by gonadotropin from pregnant mare serum; and salmon pituitary 

 plus human chorionic gonadotropin followed 24 h later by salmon pituitary plus human chorionic 

 gonadotropin plus gonadotropin from pregnant mare serum. The hormones did not induce spawning 

 when used individually. A procedure for routine spawning of Pacific mackerel is described. 



Laboratory studies of the biology of pelagic fish 

 larvae are often limited by the uncertainty of 

 collecting eggs at sea. An alternative to collecting 

 eggs at sea is the maturation and spawning offish 

 in the laboratory. This objective was met for the 

 northern anchovy, Engraulis mordax (Leong 

 1971). Another species whose larvae are under 

 study at the Southwest Fisheries Center is the 

 Pacific mackerel, Scomber japonicus Houttuyn, 

 but the eggs are not available off the southern 

 California coast during most of the year. To in- 

 crease the availability of mackerel eggs for ex- 

 perimental work, I began a study designed to 

 develop procedures for routinely spawning 

 mackerel on demand throughout the year. My 

 approach was to first find a suitable photoperiod- 

 temperature environment which would encourage 

 maturation and to subsequently induce spawning 

 with gonadotropic agents. This report contains 

 observations on the maturation of mackerel under 

 different photoperiod-temperature conditions in 

 the laboratory; results of exploratory tests with 

 hormones to induce spawning; and a description of 

 a procedure currently used to spawn mackerel. 



I followed the maturation of mackerel under 

 four photoperiods (4 h light 20 h dark, 8L16D, 

 16L8D, and ambient day length) and three 

 temperatures (15°C, 18°C, and ambient 12.8° to 



Southwest Fisheries Center, National Marine Fisheries 

 Service, NOAA, La Jolla, CA 92038. 



Manuscript accepted September 1976. 

 FISHERY BULLETIN: VOL. 75, NO. 1, 1977. 



19°C). I also examined the effectiveness of a 16°C- 

 14L10D environment for maintaining mackerel in 

 spawning condition after the normal spawning 

 season. The hormones tested for the induction of 

 spawning were gonadotropin from ground salmon 

 pituitary, human chorionic gonadotropin, and 

 gonadotropin from pregnant mare serum. The 

 importance of the photoperiod-temperature en- 

 vironment in regulating maturation in fish and 

 the use of gonadotropins for inducing spawning 

 are well known from the early review of Pickford 

 and Atz (1957), but observations on marine 

 pelagic species are still limited. These are the first 

 observations on the maturation and spawning of a 

 scombrid fish under laboratory conditions. 



METHODS 



Maturation of Mackerel Under 

 Four Photoperiods 



Knaggs and Parrish (1973) examined the 

 ovaries of mackerel from the commercial catch 

 and concluded that S. japonicus can spawn from 

 March through October but that the majority 

 spawn from April through August. Kramer 

 (1960), using sea-caught larvae as criteria, 

 concluded that spawning occurs from late April or 

 early May to August. 



The fish used in these experiments were caught 

 off the southern California coast by hook and line 



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