FISHERY BULLETIN: VOL. 75, NO. 1 



tion but the females did not spawn spontaneously 

 nor could they be satisfactorily stripped (Table 1). 

 The females ovulated within 24 h in the 10- and 

 15-mg trials and between 24 and 40 h in the 1-, 5-, 

 and 25-mg trials. Ovulated eggs were catheterized 

 from live fish in the 1- and 15-mg trials and from 

 dead fish in the 5-, 10-, and 25-mg trials. The live 

 females in the 1- and 15-mg trials were stripped as 

 soon as ovulation was detected but the fish re- 

 leased only small numbers of eggs even with 

 heavy stripping pressure. Attempted fertilization 

 resulted in less than 10 larvae in both trials. The 

 stripped eggs were translucent, measured 1.1 mm 

 in diameter, and appeared normal but nearly all 

 were not viable. 



The females that received 5, 10, 15, and 25 mg of 

 SP died within 40 h after injection. The female 

 that received 1 mg was intentionally killed at 72 h 

 for dissection. All of the females including the one 

 that received only 1 mg of SP had severely dis- 

 tended abdomens. Subsequent dissection revealed 

 that the distension was due to extremely enlarged 

 ovaries. The ovaries contained many ovulated 

 eggs which were not extruded and the females 

 were apparently egg bound. I did not see any plugs 

 or clots which impeded the flow of eggs. 



All injections of SP, 1 to 25 mg, to male mackerel 

 facilitated the stripping of milt. The milt in the 

 catheter samples before injection was thick and 

 only small amounts could be expressed. The in- 

 jections of SP brought about a thinning of the milt 

 and made stripping easier. None of the males 

 injected with SP died. 



All injections of human chorionic gonadotropin 

 (HCG), 12.5 to 500 IU, stimulated hydration and 

 ovulation but the females could not be easily 

 stripped of eggs. Ovulation occurred within 24 h in 

 the 125-, 250-, and 500-IU trials and between 24 

 and 40 h in the 12. 5-, 25-, and 50-IU trials. None of 

 the females that were alive when ovulation was 

 detected could be stripped of more than 500 eggs. 

 The number of larvae produced was negligible in 

 all trials. All of the females that received 50 or 

 more IU of HCG died within 40 h after injection. 

 The females that received 12.5 or 25 IU of HCG 

 were purposely killed at 72 h. As with SP, all of the 

 females had severely distended abdomens and 

 enlarged ovaries. All dosages of HCG facilitated 

 the stripping of milt without killing the male. 



The results of trials with pregnant mare serum 

 ( PMS) were variable. In the 1 ,000-IU trial the eggs 

 increased in size from 0.7 to 0.8 mm in diameter in 

 24 h and were ovulated by 40 h. More than 5,000 



eggs were stripped at 40 h but most of the eggs 

 were cloudy, had collapsed perivitelline mem- 

 branes, and were apparently overripe. However, a 

 few eggs were viable and a small number hatched 

 following fertilization. In the 750-IU trial, ovu- 

 lation was detected at 24 h but the eggs already 

 had collapsed perivitelline membranes and were 

 overripe. The eggs in the 300-IU trial grew to 0.8 

 mm within 24 h but did not show further im- 

 provement at 40 h. None of the females injected 

 with PMS had severely distended abdomens and 

 none were dead by 40 h after injection. At all levels 

 tested, PMS made the stripping of milt easier and 

 did not kill the injected male. 



The three combinations of hormones tested were 

 all successful in stimulating hydration, ovulation, 

 and spontaneous release of eggs. The first injec- 

 tion, 1 mg SP, of the SP-PMS trial promoted egg 

 growth from 0.7 to 0.9 mm in diameter in 24 h. The 

 second injection of 100 IU PMS 24 h later appeared 

 to stimulate the release of eggs as 50,000 eggs 

 were found in the egg strainer at 40 h. The eggs 

 were translucent, measured 1.1 mm in diameter, 

 and appeared to be of good quality but were un- 

 fertilized. However, the female extruded another 

 50,000 eggs when stripped at 40 h and these were 

 artificially fertilized with milt from the injected 

 male. About half of the eggs showed signs of 

 cleavage and approximately 10,000 larvae 

 hatched. The larvae appeared normal when 

 compared with the larval descriptions of Kramer 

 (1960) and Watanabe (1970). Some of the larvae 

 later developed into juveniles which grew to more 

 than 100 mm total length. 



The other two combinations (12.5 IU HCG ini- 

 tially and 100 IU PMS 24 h later; 1 mg SP + 12.5 

 IU HCG initially and 1 mg SP + 12.5 IU HCG + 

 200 IU PMS 24 h later) produced similar results. 

 The initial injection produced egg growth to 0.8 or 

 0.9 mm and spawning occurred after the second 

 injection but the spawned eggs were unfertilized. 

 The fish were then stripped and the eggs arti- 

 ficially fertilized. Many of these hatched and 

 produced thousands of viable larvae. All of the 

 females became bruised from the handling during 

 stripping, and died a few days after spawning. 



RECOMMENDED PROCEDURE 



A procedure for spawning mackerel has been 

 developed from the foregoing observations and the 

 method has been used since March 1975 to 

 routinely produce viable eggs. The 16°C-14L10D 



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