but also in terms of application and degree of utilization by the experimental 

 animals. Food supply seemed to be a limiting factor regardless of whether 

 or not brine shrimp were included in the diet. With the brine shrimp diet, 

 the growth rate dropped noticeably in the experiment's later stages, during 

 which the amount of food supplied was obviously inadequate for the nunnber 

 of animals present. 



With brine shrinnp as the only food involved, a second experiment 

 was undertaken to determine the effects of salinity on the growth of postlarval 

 brown shrimp. Four levels of salinity were established, viz. , 5%o, 10%o, 25%c, 

 and 40%«. These were adjusted over 48-hour periods by adding distilled or 

 concentrated sea water to the "control" sea water (ZBfoo) to obtain the desired 

 level. As in the preceding experiment, 10 animals were removed at 4- or 

 5 -day intervals for weight and length measurements. The accompanying figure 

 shows that consistently better growth was obtained in all salinity groups than 

 in the previous experiment with the diet group fed live brine shrimp, (cf. fig- 

 ure for experiment described in 

 previous section. ) This naay have 

 been partly due to the use of fewer 

 animals in the salinity test aquaria 

 (100 as against 150 animals in the 

 diet experiments). There was, how- 

 ever, significantly greater growth 

 at 25%o than at any of the other sa- 

 linity levels, this being noted at 

 all stages of the experiment. No 

 significant differences in gro^vth 

 could be detected among the other 

 salinity groups. The mean rate 

 of increase was 3. 8 rng. per day 

 (0. 6 mm. per day) with a maxi- 

 mum in Z5%o of 9. 8 mg. and 0. 8 

 mm. per day. The greater growth 

 at 25foo may be related to a de- 

 creased survival rate (more food 

 per animal), since only 36 percent 

 of the animals survived, as against 

 68 percent in each of the other sa- 

 linity groups. 



These findings suggest 

 that for immature brown shrimp 

 good growth and survival are pos- 

 sible over wide salinity ranges, 

 provided an adequate food supply 

 is available. This should stim- 

 ulate reexamination of the hypoth- 

 esis that young shrinnp require low 

 salinity levels for adequate growth. 



Laboratory growth of postlarval brown 

 shrimp at four levels of salinity. (Diet: 

 Live brine shrimp nauplii. ) 



62 



