FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



OPERATION OF THE HATCHERY 

 STOCKING THE BROOD TANKS 



The brood stock for stockiiiji: tlie tanks was sup- 

 plied by Hawaiian Tuna Packers, Ltd. The crew 

 of the sampan Amherjack seined the nsh on Janu- 

 ary 10, 1958, from reservoir No. 6, at Ewa, Onliu. 

 The tish were acclimatized to sea water in the bait 

 wells of the sampan and transported to Maui on 

 January 11-12. Some mortalities occurred dur- 

 ing the acclimatization and as a result of liandling, 

 but about 5,000 fish weighing 1,200 pounds sur- 

 vived. A total of 2,000 adults (500 males and 

 1,500 females), weighing 625 pounds, ^^■ere stocked 

 in the two brood tanks, each tank receiving 250 

 males (0.34 lb. a\erage weight) and 750 females 

 (0.30 lb. average weight). The remainder of the 

 fish were retained to replace stock that died. 



In the days that followed, dead fish were re- 

 moved from the tanks and replaced with a like 

 number of the appropriate sex. Deaths were nu- 

 merous during the first week after stocking, but 

 were practically zero by the end of the second 

 week. The total mortality from January 13 to 

 31 was 705 fish (549 females and 156 males) . The 

 mortality rate was about the same for the sexes. 



The adult fish were stocked in 1958 at a concen- 

 tration of 1 male per 3.37 square feet of bottom 

 area. Uchida and King (1962) had found that 

 production was favorable in tanks where the area 

 allotted per male was about 3 square feet. Al- 

 though in their initial experiments Uchida and 

 King used a 2 5 :1 $ sex ratio with successful 

 results, it was anticipated that better production 

 might be obtained by increasing the ratio to 

 3 $ : 1 ,J , so we used this latter ratio. 



Although the area was fenced and posted, van- 

 dals entered the hatchery on September 25 and 27, 

 1958, removing an unknown number of advdt fish. 

 As we did not wish to disturb the fish further, we 

 postponed taking a census until December 2-3, 

 1958, when production had declined. A census 

 on these dates showed that brood-tank A con- 

 tained 689 females and 216 males, a loss of 61 fe- 

 males and 34 males since stocking. Brood-tank 

 B contained 736 females and 251 males, a loss of 

 14 females and a gain of 1 male (this apparent 

 gain may have been due to miscount or to recruit- 

 ment of a juvenile that escaped capture and grew 

 to adulthood). 



In later experiments in 1958, Uchida and King 

 found that the best production of fry was observed 

 in tanks with a 3 9 : I S ratio and with about 4 

 s(juare feet of l)ottom area per male. Therefore, 

 in 1959 we stocked each brood tank witli 600 fe- 

 males and 200 males, witli eacli male being allotted 

 4.21 square feet of bottom area. A census taken 

 on December 7-8, 1959, showed that tank A con- 

 tained 604 females and 22S mules, a gain of 4 fe- 

 males and 28 males. Brood-tank B contained 668 

 females and 252 males, an increase of 68 females 

 and 62 males. Tliese increases were due, we be- 

 lieve, to recruitment of juveniles that had escaped 

 capture early in the year and had grown to ma- 

 turity. The males averaged 30.5 centimeters (12 

 in.) in length and 1.0 pound in weight, while the 

 females averaged 22.9 cm. (9 in.) in length and 

 0.5 pound in weight when the brood stock was 

 counted in December 1959. 



FEEDING SCHEDULES 

 Adults 



In 1958, the brood stock was usually fed twice 

 daily except on Sundays. The fish were fed once 

 every Sunday until June and were not fed on 

 Sundays thereaftei-. The daily ration for tlie to- 

 tal brood stock ranged from 5 to 12 pounds, de- 

 pending on how readily the fish were feeding. 

 An average daily ration of 4 pounds of Purina 

 trout chow (developer) per 1,000 adults seemed to 

 satisfy the needs of the fish during their most pro- 

 ductive period. The kinds of feed used in 1958, 

 with the price per pound, are shown in table 9. 

 In January to March, 1958, the adults were fed 

 a miljrun-fish meal mixture (4:1 ratio). In 

 April, the feed iii one brood tank (B) was changed 

 to rabbit ration (pelletized), a better quality feed. 

 The change in feed did not result in an increase 

 in fry production. The rabbit ration was supple- 

 mented in July with Purina trout chow and in 

 August through December 1958 the fish in botli 

 brood tanks were given Purina feed. 



In 1959, the brood stock was fed twice daily, 

 except on Sundays, from February through Octo- 

 ber, and once daily from November through De- 

 cember. They were fed once on Sundays until 

 May and were not fed thereafter on Sunday. 

 Their daily ration was 3 to 6 pounds of Purina 

 developer or large fingerling feed. The kinds, 

 costs, and amounts of feed used in 1959 are shown 

 in table 10. 



