46 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



ment. Outbreaks of infectious pancreatic necrosis, 

 believed to be caused by a virus, were not con- 

 trolled by any of the methods tried. Strict sanita- 

 tion, prevention of overcrowding in the fry-tank 

 compartmients, and periodic prophylactic treat- 

 ments were found to be good control measures for 

 preventing outbreaks of disease. 



Several factors were found to affect fry produc- 

 tion. The spawning rate was increased during the 

 winter months by artificially raising the tempera- 

 ture of the water. Only a slight rise was neces- 

 sary to increase spawning frequency, but 

 prolonged constant high temperature seemed to 

 have a detrimental effect. 



A sex ratio of 3 9 : 1 3 resulted in the highest 

 reproductive rate. An allotment of about 4.0 

 square feet of bottom area per male and 1.0 square 

 foot per individual provided the most optimum 

 conditions for courtship and spawning. Brood 

 stocks fed high-quality feed had higher produc- 

 tion per female than those fed low-quality feed. 

 A significantly higher fry production occurred in 

 brackish water (about 10 "/oo) than in fresh water. 



The growth of young fish was influenced by 

 environmental factors. Significantly faster 

 growth rates were found among young reared in 

 less crowded tanks than in crowded tanks. Young 

 reared on high-quality feed also evinced a much 

 faster growth rate than those fed low-quality feed. 

 The growth of young fish in brackish water of a 

 salinity of about 10 °/oo was remarkably fast. 



An investigation of cannibalism indicated that 

 juveniles averaging 20.4 mm. (about 0.75 in.) can 

 kill or consume fry up to 10 mm. (about 0.38 in.) 

 in length, and juveniles averaging 64.4 mm. (about 

 2.5 in.) in length are able to kill or consume 

 smaller juveniles up to a maximum size of 24.5 

 mm. (about 1 in.). Starved juveniles evinced a 

 much more aggressive response than well-fed 

 juveniles to fry introduced into their tanks. 



LITERATURE CITED 



Atz, James W. 



1954. The peregrinating tilaiiia. Animal Kingdom, 

 vol. 57, no. 5, p. 148-155. 

 Baerends, G. p., and J. M. Baerenus-Van Roon. 



1950. An introduction to the study of the ethology 

 of cichlid fishes. Behaviour, Supplement 1, 243 p. 

 Bbock, Vernon E. 



1954. A note on spawning of Tilapia »iiissumbica in 

 sea water. Copeia, 1954, no. 1, p. 72. 



Brock, Vernon E., and Michio Takata. 



1955. Contribution to the problems of bait fish cap- 

 ture and mortality, together with experiments in 

 the use of tilapia as live bait. Territory of 

 Hawaii, Industrial Research Advisory Council 

 Grant No. 49, Final Report, 39 p. 

 Chen, Tuno-Pai. 



1953. The culture of tilapia in rice paddies in 

 Taiwan. Chinese American Joint Commission on 

 Rural Reconstruction, Fisheries Series, no. 2, 

 30 p. 

 Chimits, Pierre. 



1955. Tilapia and its culture — a preliminary bibli- 

 ography. Food and Agricultural Organization, 

 Fisheries Bulletin, vol. 8, no. 1, p. 1-33. 



1957. The tilapias and their culture. Food and 

 Agricultural Organization, Fisheries Bulletin, 

 vol. 10, no. 1, p. 1-24. 

 Davis, Herbert S. 



1946. Care and diseases of trout. Revised ed. U.S. 

 Fish and AVildlife Service, Research Report 12, 

 98 p. 



1953. Culture and diseases of game fishes. Univer- 

 sity of California Press, Berkeley, 332 p. 

 DoiDOROFF, Peter. 



1957. Water quality requirements of fishes and 

 effects of toxic substances. The Physiology of 

 Fishes. Vol. 2, Behavior. Academic Press, Inc., 

 New York, p. 403-430. 

 Fish, G. R. 



1955. The food of tilapia in E. Africa. Uganda 

 Journal, vol. 19, no. 1, p. 85-89. 



HiDA, Thomas S., Joseph R. Harada, and Joseph E. 

 King. 

 1962. Rearing tilapia for tuna bait. U.S. Fish and 

 Wildlife Service, Fishery Bulletin 198, vol. 62, 

 p. 1-20. 

 INNES, William T. 



1951. Exotic aquarium fishes. 12th ed. Innes 

 Publishing Co., Philadelphia, 521 p. 

 June, Fred C. 



1951. Preliminary fisheries survey of the Hawaiian- 

 Line Islands area. Part III. The live-bait skii)- 

 jack fishery of the Hawaiian Islands. U.S. Fish 

 and Wildlife Service, Commercial Fisheries Re- 

 view, vol. 13, no. 2, p. 1-18. 

 King, Joseph E.. and Peter T. Wilson. 



1957. Studies on tilapia as skipjack bait. U.S. Fish 

 and Wildlife Service, Special Scientific Report — 

 Fisheries No. 225, 8 p. 

 Lagler, Karl F. 



1956. Freshwater fishery biology. 2d ed. Wm. C. 

 Brown Co., Dubuque, Iowa. 421 p. 



Le Roux, p. J. 



1956. Feeding habits of the young of four species of 

 tilapia. South African Journal of Science, vol. 53, 

 no. 2, p. 33-37. 

 Lowe, Rosemary H. 



19.55. The fecundity of tilapia species. East African 

 Agricultural Journal, vol. 21, no. 1, p. 45-52. 



