20 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The natural food supply of the tilapia was sup- 

 plemented in each pond during the study period 

 by a daily feeding of rice bran. 



Kuliouou Pond 



This brackish-water pond is about 3 acres in 

 extent and has a salinity of about 20 "/oo- King and 

 Wilson (1957) obtained 105 pounds of bait-size 

 tilapia from this pond on one seining trip in 1956. 

 In 1957 a more detailed study of the pond was 

 initiated to obtain an estimate of the size of the 

 brood stock and the extent of production of young 

 fish. Appendix table 1 gives the population esti- 

 mates and summary of the fish removed. 



Kuliouou Pond failed to yield any bait-size tila- 

 pia in four seining trips in 1957. The catch made 

 on three of these trips is shown in appendix table 

 1. The adult population, estimated at the end of 

 the experiment, was about 1,400 pounds. On each 

 occasion, nests were observed on the bottom of the 

 pond and evidence of spawning (females carrying 

 ova or young in the mouth) was noted. The pond 

 contained a large number of predators, wliich with 

 the cannibalistic traits of the tilapia, practically 

 eliminated all young fish. 



Ewa Pond No. 6 



This fresh-water pond, with few predators other 

 than crayfish, was a much better source of bait- 

 size tilapia. During 1956, King and Wilson 



(1957) obtained 436 pounds of bait-size tilapia in 

 five seining trips to this pond. Nine seining trips 

 in 1957 yielded 882 pounds of bait-size fish. The 

 catch obtained on six of these trips is given in ap- 

 pendix table 1. The average catch of bait per trip 

 was slightly higher in 1957 than in 1956. 



Using the mark (fin clipping) and recovery 

 method, the adult tilapia population in Ewa 

 Pond No. 6 was estimated to be about 6,000 pounds 

 when sampled in April and again in July 1957. 

 The annual production of bait-size fish was, there- 

 fore, approximately 147 poixnds per 1,000 pounds 

 of adults. In the Paia, Maui, hatchery (this re- 

 port) a brood stock weighing about 800 poiuids 

 produced about 3,300 pounds of bait-size fish per 

 year, or 4,125 pounds of bait per 1,000 pounds of 

 adults. 



Although the adult tilapia population in this 

 pond was fed rice bran daily, cannibalism prob- 

 ably reduced the amount of bait available. As 

 reported by King and Wilson (1957), it was dif- 

 ficult to harvest the crop of young fish. Seining 

 requires a rather large crew and is not efficient 

 because of the tendency of the fish to burrow in 

 the mud or hide in the spawning beds. There- 

 fore, we believe that, in all respects, the large- 

 scale production of bait-size tilapia is more prac- 

 ticable by the tank-culture method than by the 

 uncontrolled pond-cultui-e method. 



' Less than 3 Inches long. 

 ' 3 to 8 Inches long. 

 ' Greater than 8 Inches. 



• Large female';, totaling 464 pounds, were marked and transferred to the Kuliouou Pond from this haul. 

 > Captured unmarked: marked and returned. 



« Greater than 6 inches. 



' Catch not examined for marked fish. 



' Including 464 pounds of flsh Oarge females) added March 8 from Ewa Pond No. 6. 



• Following Chapman (1948). 



U.S. GOVERNMENT PRINTING OFFICE: 1962 O — 619347 



