22 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



ferior to nehu (Sfolephoni.s purpurem), the prin- 

 cipal bait used in the skipjack fishery, it was on 

 the other hand, liardier than nelni and could 

 tolerate a wider ranjre of salinity and lower oxygen 

 concentrations. 



In view of the reported success in using young 

 tilapia as a tuna bait fish, consideration was given 

 to devising rearing methods that would be eco- 

 nomically and biologically feasible for producing 

 adequate numbers of fish of proper size. Two im- 

 mediate possibilities presented themselves: pond 

 culture, whereby existing ponds on the islands 

 would be utilized with some modifications; and 

 tank culture, with separate spawning tanks and 

 fi-y-rearing or nursery facilities. 



King and Wilson (1957: p. 8) utilized bait-size 

 tilapia obtained from private ponds and reser- 

 voirs for their sea trials and after a number of 

 bait-seining operations concluded that — 



it does not appear that the rearing of tilapia for bait pur- 

 poses can be done most effectively in water reservoirs and 

 natural ponds with little control over spawning, canni- 

 balistic traits of the species, and predation, and with 

 the difficulty of harvesting the fish efficiently at an 

 optimum size. 



It was anticipated that tank culture of the fish 

 under controlled conditions might prove to be a 

 more efficient and economical way to produce bait- 

 size tilapia. As a result, a study of tank culture 

 of tilapia on a pilot-plant scale was initiated at 

 the Bureau of Commercial Fisheries Biological 

 Laboratory at Honolulu. The primary objectives 

 of this study were to determine the physical and 

 biological problems associated with tank culture 

 and the potentialities of producing bait-size tilapia 

 in sufficient quantities under controlled conditions 

 in a hatchery-type operation. 



The pilot plant was constructed on the grounds 

 of the laboratory in October 1956 and experiments 

 were carried on there until July 1958, after which 

 the facilities were transferred to more spacious 

 grounds adjacent to the laboratory's new docksite 

 building at Kewalo Basin, Honolulu. Studies 

 continued at the Kewalo plant until September 

 1959. While the purpose of the pilot plant was 

 primarily to examine the general problems asso- 

 ciated with production of bait-size tilapia, the 

 Kewalo plant .studies were designed to obtain a 

 more detailed and quantitative evaluation of tank 

 culture and to assess the various factors associated 



with variations in reproductive, survival, and 

 growth rates. j 



The purposes of this report are to discuss our j 

 eflforts in e.stablishing operational procedures and 

 basic requirements that would be applicable to a 

 commercially operated tilapia hatchery, to present 

 our observations and conclusions on reproduction 

 and growth, and to describe the cannibalism, pre- 

 dation, and diseases of tilapia obsem-ed during the 

 experiments. 



As work progressed, the need for information 

 on other rearing methods became evident and a 

 study of pond culture of tilapia under controlled 

 conditions was begun by the Hawaii Division of 

 Fish and Game at Kaneohe, Oahu, under contract 

 with the (Territorial) Economic Planning and 

 Coordination Authority (EPCA) and the Bureau 

 of Commercial Fisheries. Production of bait- 

 size tilapia in ponds under uncontrolled conditions 

 was investigated to some extent by King and Wil- 

 son (1957) during the summer of 1956. 



The Maui Fisheries and Marine Products Co., 

 Ltd., expressed an interest in establishing a 

 tilapia hatchery on a semicommercial basis, fol- 

 lowing our initial success in producing bait-size 

 tilapia at the pilot plant. A contract was signed 

 with Maui Fisheries, the Hawaii Division of Fish 

 and Game, and the Bureau of Commercial Fish- 

 eries, as principals, late in December 1957, for the 

 operation of a tilapia-rearing plant at Paia, Maui. 

 A fishery biologist, supplied by the Bureau, was 

 placed in charge of the plant to obtain detailed 

 records of the production and of operational costs. 

 The Paia hatchery was operated for 2 years and 

 the results have been reported by Hida et al. 

 (1961). 



In frequent references throughout this report 

 to the various stages of development of tilapia, we 

 have tried to conform to generally accepted ter- 

 minology, but in some instances we found com- 

 binations of categories more suitable and in other 

 ways we have diverged from ordinary usage. The 

 terminology that we have employed is defined as 

 follows: 



Fry. — Includes both the prolarval (yolk-bear- 

 ing) and postlarval (nonyolk-bearing) stages. 

 Includes tilapia up to 19.0 mm. (0.75 in.) in length. 



Juvenile. — Stages between fry and adult, with 

 a range in size from about 20 to 100 mm. (0.75 to 

 4 in.). 



