NOTES 



GROWTH AND FOOD CONVERSION OF 

 RAINBOW TROUT REARED IN 

 BRACKISH AND FRESH WATER 



Although brackish water culture of rainbow 

 trout (Salmo gairdneri Richardson) has been 

 practiced in other countries for years ( Awakura, 

 1962; Awakura, Shibata, and Honma, 1962; 

 Sato, 1965; Jensen, 1967), few attempts have 

 been made to culture this euryhaline species in 

 brackish water in the United States (Leon, 

 1970). The following study was designed to 

 study the growth, food conversion, and survival 

 rates of rainbow trout reared from fingerling 

 to market size in brackish and fresh water. 



feeding table (Oshima, 1968). The entire pop- 

 ulation of each tank was weighed and counted 

 monthly. Temperatures, ammonia, salinity, and 

 dissolved oxygen levels were determined bi- 

 weekly. Ammonia levels were below 0.3 ppm 

 and oxygen concentrations were above 7.0 ppm 

 throughout the experimental period. After 16 

 weeks (December 4, 1970-March 26, 1971) the 

 experiment was terminated. Growth data was 

 tested for statistical significance by the method 

 of Duncan (1955), 



Results and Discussion 



Acclimation to brackish water 



Materials and Methods 



Six 1.8-m diameter round fiber glass tanks 

 with a water depth of 0.6 m were used as ex- 

 perimental culture tanks (Andrews et al,, 1971) . 

 Fresh water from a deep well (22°C) or brackish 

 water ( 25-30^-^ r) from the Skidaway River, 

 Savannah, Ga., was pumped into each tank 

 through flow control nozzles at a rate of 19 

 liters/min (1,3 hr/exchange) . Since the tem- 

 perature of the brackish water varied and the 

 experimental tanks were located out-of-doors, 

 water temperatures were not controlled. 



Four experimental tanks were stocked with 

 rainbow trout averaging 60 g each at an initial 

 density of 7.2 kg fish/m^ and two were stocked 

 at a density of 14.4 kg fish/m^. Fish in two of 

 the tanks containing 7.2 kg/m^ and the tanks 

 containing 14.4 kg/m^ were acclimated to brack- 

 ish water by gradually changing the fresh to 

 brackish water ratio of incoming water. Figure 

 1 shows the changes in salinity during the 9-day 

 acclimation period. 



Each group was fed a commercial pelleted 

 trout feed' twice daily according to Leitriz's 



A survival rate of 99.5% was obtained in the 

 two groups acclimated to brackish water during 

 the 9-day period and the following 10 days in 

 which salinity was 30;^^. These results are in 

 contrast to a previous report that over 40% 

 mortality was obtained when rainbow trout 

 weighing approximately 60 g each were adapted 

 to 30%o salinity (Oshima, 1968), 



30 

 25 -I 



CL 



20 



15 - 



>- 



-J 



<^ 5 



10 



DAY 



' Donated by Agway, Inc., Syracuse, N.Y. 



Figure 1. — Changes in salinity during the 10-day period 

 in which the rainbow trout fingerlings were acclimated 

 to brackish water. 



1293 



