REARING TILAPIA FOR TUNA BAIT 



13 



Fish afflicted with the condition dia<rnosed as acute 

 catarrhal enteritis were supplied with an increased 

 flow of fresii water, since there is no known treat- 

 ment. 



In 10,59, each newly filled tank was <riven a 

 prophylactic treatment of o p.p.m. potassium per- 

 manganate or 0..5 p.p.m. copjier sulphate before 

 tlie fry were added. This i)rocednre seemed to 

 be eti'ective in checking Trirhodina outbreaks. 

 Although we have no measure of the effect of 

 wind-blown dust and debris on the disease prob- 

 lem, we believe that the causative organisms of 

 some of the infections could have been introduced 

 through the excessive amounts of road dust that 

 occasionally contaminated the tanks. Early de- 

 tection of disease was often difficult because of rain 

 or strong winds that prevented our observing the 

 condition of the fish. 



DUTIES OF THE HATCHERY OPERATOR 



"When operated on an experimental basis, the 

 Paia plant required one person full time; on a 

 commercial basis we estimate that the work load 

 would not have been too great for one man half 

 time. 



The daily tasks and time required to perform 

 them were as follows : 



1. Dipnetting the young — 1/2 hour to 2 hours. 



2. Counting the young — 1,4 hour to 3 hours. 



3. Feeding adult fish twice a day — 1^4 hour. 



4. Feeding young three times a day — 14 to 1/2 

 hour. 



5. Removing the dead fish — 10 minutes to 3 

 hours. 



6. Checking inflow and drain pipes — 14 to 1/2 

 hour. 



Some irregularly occurring tasks were as fol- 

 lows: 



1. Treating sick fish: weighing chemicaLs, ap- 

 plying treatment, checking I'esults, flushing out 

 tanks with fresh water — % hour to 4 hours. 



2. Transferring young from fry tanks to hold- 

 ing tank.s — 2 men 1/2 day a week during productive 

 season. 



3. Cleaning fry tanks — % day a week. 



4. Constructing equipment, mending nets, 

 et cetera — 2 hours a week. 



5. Measuring oxygen concentrations — 1 hour 

 if done once a week. 



6. Caring for grounds — 1 day every 4 weeks 

 with power mower. 



7. Trucking bait-size fish to docksite — truck 

 driver and helper, 1 day a week during productive 

 season. 



8. Acclimatizing bait fish — Old method: 1 day 

 a week during productive season. New method: 

 4 hours a week during productive season. 



PRODUCTION OF BAIT-SIZE TILAPIA 



1958 PRODUCTION 



By the end of December 1958, an estimated 

 412.530 bait-size (1.5 to 2.5 in.) tilapia, weighing 

 1,429 pounds (204 buckets-), had been removed 

 from the hatchery. Of this amount, 189,237 fish 

 weighing 630 pounds (90 buckets) were delivered 

 to Maui Fisheries and Marine Products, Ltd. ; the 

 rest were used in experimental fishing from the 

 Bureau of Commercial Fisheries research vessels 

 Hugh M. Smith and Charles H. Gilbert. On Jan- 

 uary 8, 1959, an estimated 146,346 fish weighing 

 531 pounds (76 buckets) were received aboard the 

 Smith and the Gilbert. The average individual 

 weight of fish in each of the delivered lots, esti- 

 mated by subsampling, ranged from 1.17 grams 

 (39 nrni. or 1.5 in. length) to 2.18 g. (49 mm. or 

 1.9 in. length). The overall average weight was 

 1.59 g. (44 mm. or 1.7 in. length). 



If we subtract from the estimated total produc- 

 tion (1,074,076) the number of fish delivered 

 (558,876) up to Januaiy 8, 1959, and the observed 

 mortality (48,806), we obtain a remainder of 466,- 

 394 fish, the theoretical balance on hand. Follow- 

 ing the January 8th delivei-y to the Smith and 

 Gilbert, 64 fry tanks each containing an estimated 

 6,000 young fish approaching bait size remained 

 at the Paia plant. This stock of 384,000 fish, bar- 

 ring accident, should equal 190 buckets of bait by 

 the end of February. The di ti'erence between 466,- 

 394 and 384,000 equals 82,394 or the unobserved 

 los.ses resulting from cannibalism, predation by 

 night herons and dragonfly nymphs, and from oth- 

 er causes. In terms of buckets, the total prothic- 

 tion, therefore, amounted to 470 buckets. In terms 

 of production per unit area, the 1958 production 

 was equal to 9,200 pounds (4.6 tons) of fish per 

 acre per year, based on the 280 buckets actually 

 used, or 15,400 pomids (7.7 tons) per acre per year, 

 based on the estimated total production. 



• One bucket equals 7 pounds of fish. 



