FISHERY BULLETIN: VOL. 70. NO. 3 



in 0.40-ha ponds. His data are not directly 

 comparable, however, as he fertilized the ponds 

 in addition to feeding the fish. A rough cor- 

 rection may be made by subtracting growth 

 achieved in unfed groups of fish. By doing so, 

 a mean of 42% is obtained for T. mossambica in 

 seven experiments starting with brood stock and 

 lasting a single growing season. The much 

 poorer showing of T. macrocephala in the present 

 experiment is believed to be partly due to the 

 large proportion of liver included in the diet 

 (Table 1) . Substantial amounts of uneaten liver 

 were often removed from the tanks during daily 

 cleaning. Also, the population density in 

 Swingle's ponds was about two orders of mag- 

 nitude less than in the present experiment, which 

 may bear on the diiference in food conversion. 

 His ponds were about the size of the larger ones 

 used by Chen and Prowse ( 1964) , so their finding 

 of greater growth in larger ponds may account 

 for some of the superiority in growth found by 

 Swingle. 



ACKNOWLEDGMENTS 



My thanks are due to Dr. Ralph Hile for sug- 

 gesting an experiment to study space effects. 

 Initial stocks were contributed by the National 

 Marine Fisheries Service, Southwest Fisheries 

 Center, Honolulu Laboratory through the kind- 

 ness of Heeny S. H. Yuen and Robert T. B. Iver- 

 sen. George F. Slusser developed the diets and 

 experimental procedures. The populations were 



maintained by Martin G. Beam, Jimmy R. 

 Chrnaoski, and Judy A. Trauth. 



As part of the 0. E. Sette dedicatory volume, 

 I gratefully dedicate this small contribution to 

 him. He was my first research supervisor ( 1938- 

 45), and I owe a very great deal indeed to his 

 encouragement, advice, and instruction during 

 those formative years of my career. 



LITERATURE CITED 



Aronson, L. R. 



1949. An analysis of reproductive behavior in the 

 mouthbreeding cichlid fish, Tilapia macrocephala 

 (Bleeker). Zoologica 34:133-158. 

 Chen, F. Y., and G. A. Prowse. 



1964. The effect of living space on the growth rate 

 of fish. Ichthyologica 3:11-20. 

 Fox, W. W., Jr. 



1970. An exponential surplus-yield model for op- 

 timizing exploited fish populations. Trans. Am. 

 Fish. Soc. 99:80-88. 



Perlmutter, a., and E. White. 



1962. Lethal effect of fluorescent light on the eggs 

 of the brook trout. Progr. Fish-Cult. 24:26-30. 

 SiLLIMAN, R. P. 



1971. Advantages and limitations of "simple" fish- 

 ery models in light of laboratory experiments. 

 J. Fish. Res. Board Can. 28:1211-1214. 



Swingle, H. S. 



1960. Comparative evaluation of two tilapias as 

 pondfishes in Alabama. Trans. Am. Fish. Soc. 89: 

 142-148. 

 Thompson, W. F., and F. H. Bell. 



1934. Biological statistics of the Pacific halibut 

 fishery. (2). Effect of changes in intensity upon 

 total yield and yield per unit of gear. Rep, Int. 

 Fish. Comm. 8, 49 p. 



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