a poorer food conversion efficiency and survival 

 rate. The lower survival rate (87%) of this 

 group resulted in a total production (final den- 

 sity) only slightly greater than the saltwater 

 group stocked at the same density. 



A faster growth rate, better survival, and bet- 

 ter food conversion were obtained at the lower 

 stocking density brackish group thus demon- 

 strating the effects stocking density has on these 

 variables. The fact that oxygen was over 7 ppm 

 in all groups throughout this experiment indi- 

 cates that stocking density and not oxygen stress 

 accounted for this reduction in performance. 



Conclusions 



Duncan, D. B. 



1955. Multiple range and multiple F tests. Bio- 

 metrics 11:1-42. 

 Jensen, K. W. 



1967. Saltwater rearing of rainbow trout and salm- 

 on in Norway. Food Agric. Organ. U.N. EIFAC 

 Tech. Pap. 3:43-48. 



Leon, K. A. 



1970. Some aspects of the comparative biology of 

 an interracial hybrid rainbow trout and the two 

 parental stocks. Ph.D. Thesis, Univ. Washington, 

 Seattle, 125 p. 



OSHIMA, Y. (editor). 



1968. Suisan yoshoku handbook. Suisan-Sha 

 Tokyo, 535 p. 



Sato, M. 



1965. On the culturing of rainbow trout in salt 

 water. Yoshoku/Fish Cult. 2:58-63. 



The fact that temperature was not constant 

 in all groups precluded a conclusive comparison 

 of the performance of rainbow trout in brackish 

 and fresh water. Nevertheless, the following 

 conclusions can be made from these experimental 

 data: 



1. Rainbow trout were converted from fresh 

 to 30^f salinity in a period of 9 days and were 

 reared to market size at this salinity. 



2. Trout fingerlings averaging 60 g each were 

 reared to 266 g in 21°C fresh water with a rapid 

 individual growth rate and an acceptable sur- 

 vival and food conversion rate. 



3. Survival and growth rates and food efficien- 

 cies were excellent for trout reared in brackish 

 water at an average temperature of 13.5°C. 



Literature Cited 



Andrews, J. W., L. H. Knight, J. W. Page, Y. Matsuda, 

 AND E. E. Brown. 



1971. Interactions of stocking density and water 

 turnover on growth and food conversion of chan- 

 nel catfish reared in intensively stocked tanks. 

 Prog. Fish-Cult. 33:197-203. 

 Awakura, T. 



1962. On the tolerance of rainbow trout, Salmo 

 gairdneri irideus Gibbons, to salt water. I. [In 

 Japanese.] Sci. Rep. Hokkaido Fish Hatchery 17: 

 41-48. 

 Awakura, T., H. Shibata, and K. Honma. 



1962. Some observations on the breeding of rain- 

 bow trout, Salmo gairdneri irideus Gibbons, in 

 salt water. [In Japanese.] Sci. Rep. Hokkaido 

 Fish Hatchery 17:49-57. 



Takashi Murai 

 James W. Andrews 



Shidaway Institute of Oceanography 

 55 West Bluff Road 

 Savannah, GA 3H06 



THE AMOUNT OF SPACE AVAILABLE 

 FOR MARINE AND FRESHWATER FISHES 



Cohen (1970) has presented rather careful esti- 

 mates of the total number of fish species in the 

 world and in each of eight ecological groupings. 

 He found that an "astonishingly high percent- 

 age" of bony fishes live in freshwater habitats. 

 According to Cohen's analysis, 41.2% (8,275 

 species) of all fish species live in fresh water 

 (includes both primary and secondary fresh- 

 water fishes). He indicates that this high per- 

 centage must reflect the degree of isolation pos- 

 sible in freshwater environments and refers to 

 the great variety of habitats and ecological 

 niches in fresh water and also along tropical 

 shores. 



The great number of freshwater fish species 

 becomes even more striking if the volume of 

 fresh water in the world is compared to the vol- 

 ume of the oceans. Indeed, the mode of specia- 

 tion and the structure of the niche appear highly 

 divergent between the two environments. The 

 oceans account for 97% of all the water in the 



1295 



