SUMMARY 



1. Nine experimental populations of the guppy, 

 Lebistes reticulatus, were established in 20-1. 

 aquariums. 



2. Groups of three ]iopulations selected by lot 

 were fed at rates 0.5, 1.0, and 1.5 times the 

 "standard" diet. 



3. Amount of food, temperature, space, and light 

 were held constant during the course of the 

 experiment. 



4. During weeks 21 to 28 of the expermient, 

 mean weights of populations at the 0.5, 1.0, and 

 1.5 diet levels were 14.5, 26.0, and 36.6 g., respec- 

 tively; mean numbers of fish were 110, 145, and 

 149. 



5. The greater mass of the populations at the 

 higher diet levels than at the lowest reflected 

 faster growth more than better survival. 



6. Exploitation of the po])ulations in each diet 

 level group of three was applied at rates of 0.25, 

 0.33, and 0.50 per 3-week reproductive period. 

 There were, thus, nine diet-exploitation combina- 

 lions. Exploitation was started during weeks 29 

 to 34, wlien the comp<isition of the populations 

 was reasonably stable, and continued to the end 

 of the experiment during weeks 70 to 72. 



7. Populations responded to exploitation with 

 an initial drop in nimibers and weight, followed by 

 near stability in weight at new lower levels (num- 

 bers were less stable, owing to entrance and mor- 

 tality [through cannibalism or otherwise] of bro<ids 

 of new-born fish). 



,s. Yields in weight during tlie final 14 weeks of 

 the experiment were reasonably stable and were 

 used in the study of the interaction between food 

 level and exploitation. 



9. Curves of yield as related to biomass and 

 exploitation rate at each diet level showed that 

 the relation of yield to exploitation fate was inde- 

 pendent of diet level. 



10. Yields were maximum near the 0.33 ex- 

 ploitation rate for all diet levels, and absolute 

 amounts were 2.4, 3.9, and 5.S g. \iev 3-week 

 period for the 0.5, 1.0, and 1.5 diets, respectively. 



1 1 . The maximum yields represented conversion 

 of about 25 percent of the food consumed, for all 

 three diet levels. 



12. Results suggest that, to the extent that 

 commercially fished populations belKue similarly 

 to the laboratory populations, management strat- 



egies may be applied regardless of abundance of 

 food organisms. 



ACKNOWLEDGMENTS 



Most of the initial stock of guppies was donated 

 from an aquarium maintained by Julius Rockwell, 

 Jr. Part of the stock remained from experiments 

 performed by Nancy Maynard. John Pricci, Wil- 

 ham Frazier, and Josephine Dickens fed and 

 maintained the fish (all five of these people were 

 members of the Bureau of Commercial Fisheries). 

 L. AI. Dickie and his staflf of the Fisheries Re- 

 search Board of Canada furnished useful sug- 

 gestions which were followed in revising the 

 manuscript. 



LITERATURE CITED 



Beverton, I?.\ymond J. H., and S. J. Holt. 



19.57. On the dynamics of exploited fisli populations. 

 Great Britain Ministry of Agriculture, Fisheries, 

 and Food; Fishery Investigations, Ser. 2, Vol. 19, 

 .532 pp. 

 Innes, William T. 



194.5. Exotic aquarium fishes. Philadelphia, Innes 

 Publ. Co., 507 pp. 

 Jensen, A.vge J. C. 



1928. The relation between the size of the plaice 

 stock and the quantity of "first-class plaice-food" 

 in certain parts of the Limfjord. Rep. Danish 

 Biol. Sta. 34(5) : 87-98. 

 Lewis, Willi.\m M. 



1963. Maintaining fishes for experimental and 

 instructional purposes. So. 111. Univ. Press, Car- 

 bondale. 111., 100 pp. 

 Palohbimo, Jyri E., and L. M. Dickie. 



1965. Food and growth of fishes. I. A growth curve 

 derived from experimental data. J. Fish. Res. Bd. 

 Canada 22(2) : .521-.542. 

 SiLLiMAN, Ralph P. 



1948. Factors affecting population levels in Lebistes 

 reticulatus. Copeia 1948 (l):40-47. 

 SiLLiMAN, Ralph P., and J. S. Outsell. 



1958. Experimental exploitation of fish populations. 

 U.S. Fish Wildl. Serv., Fish. Bull. .58: 21.5-2.52. 

 Zheltenkova, M. V. 



1958. O vhyanil uslovil otkorma na populyatsiyu 

 ryb (On the effect of feeding conditions on a fish 

 population). Trudy Vses. Nauch.-Issled. Inst. 

 Mors. Ryb. Khoz. Okean. (VNIRO) 34: 102-126. 

 Fish. Res. Bd. Canada (St. Andrews N. B. Trans. 

 Ser. 240) . 

 1961. O bespechennost ' pischei vida, populyatsil i 

 piko IcnnI u ryb (The supply of food for a species, 

 a population, or a year class of fish). Akad. Nauk 

 S.S.S.R. Trudy Sovesch. Ikhtiol. Komm., No. 13, 

 82-93 (Trans. N.S. 2, Fish. Lab. Lowestoft, Eng- 

 land, 1963, 17 pp.). 



POOD LEVEL AN.D EXPLOITATION IN FISH POPULATIONS 



439 



fi U.S. GOVERNMENT PRINTING OFFICE : 1968 O - 310-319 



