TANK CULTURE OF TILAPIA 



23 



Bait size. — Juveniles suitable for skipjack bait 

 range in size from about 38 to 51 mm. ( 1.5 to 2 in.) ; 

 however, on several occasions juveniles falling out- 

 side tliis length range have been used for bait. 



Young. — A general category that includes fry 

 and juveniles. 



Adult. — Mature fish tliat are potential breeders 

 and are distinguishetl by the display of coloration, 

 especiallj' by the males in the reproductive phase. 

 Larger tlian 100 mm. (4 in.) in length. 



The length measurement used in this report is 

 fork length; that is, the length from tip of the 

 snout to ends of the middle caudal rays. Body 

 measurements (length and weiglit) were made in 

 both English and metric units during the early 

 phases of the investigation. However, all origi- 

 nal measurements in English units have been con- 

 verted to their equivalent in metric units, and 

 where applicable or when appropriate the Eng- 

 lish units are given in parentlieses. Reference to 

 plant facilities is either to the pilot plant con- 

 structed on the grounds of the Bureau's Honolulu 

 Laboratory or to the Kewalo plant located at 

 tlie Kewalo Basin docksite. 



We gratefully acknowledge the advice and sug- 

 gestions given us by the Bait-fish Research Co- 

 ordinating Committee composed of biologists of 

 tlie Hawaii Division of Fish and Game, the LTni- 

 versity of Hawaii, and the Bureau of Commercial 

 Fisheries, Honolulu, and representatives of the 

 Hawaiian Tuna Boat Owners Association and the 

 Hawaiian Tuna Packers, Ltd. 



CULTURE METHODS 

 REARING FACILITIES 

 Pilot Plant 



Tliree redwood raceway-type tanks, each 5 feet 

 wide by 20 feet long and 3 feet deep, with a ca- 

 pacity of 1,400 gallons, were constructed on the 

 grounds of the laboratoiy in October 1956 (fig. 

 1 ). The floors sloped downward toward the out- 

 flow end of the tank at the rate of 1 inch for each 

 10 feet of length. The outflow, located in one 

 coi-ner of the tank, consisted of a removable stand- 

 pipe that slipped into a hole in the floor of the 

 tank and connected with a gate valve and drain- 

 pipe on the outside. Baffle l>oards and a brass 

 screen enclosed a triangular area occupietl by tiie 

 standpipe. The bailie boards were raised about 



Figure 1. — A redwood raceway tauk at the pilot plant. 



•1 inches alwve the floor. Thus, the outflowing 

 water was drawn from the floor of the tank and 

 aided in removing detritus from the tanks. The 

 brass .screen prevented the fry from being car- 

 ried out through tiie drain. The inflow, situated 

 on the opposite end of the tank, was a faucet from 

 which fresh water from the Honolulu water sup- 

 ply was dripped into the tank at the rate of one- 

 half to 1 gallon a minute. The tanks were given 

 a coat of aluminum paint before being used. 



Initially, these three tanks were used as brood 

 or spawning tanks. With the onset of fry pro- 

 duction in December 1956, it was necessary to 

 convert one of the tanks to a frj'-rearing tank. 

 Continued fry production created a need for more 

 rearing space. In June 1957, a fourth redwood 

 raceway-type tank, 30 inches wide by 30 feet long 

 and 30 inches deep, with a capacity of about 1,250 

 gallons, was const met ed adjacent to the other 

 tanks. Screens of fine-meshed Monel stretched 

 over square wooden frames were used to partition 

 the tank into six approximately equal compart- 

 ments. P^ach compartment iiad a siphon-type 

 drain of plastic tubing. A standpipe drain was 

 placed at one end of the tank in the event tliat the 



