FISHERY BULLETIN: VOL. 70, NO. 1 



100 



Figure 2. — Mean and standard error for percentage of 

 animals surviving after 8 weeks of growth with two 

 types of aeration. 



STOCKING DENSITY STUDY 



Stocking densities higher than 40 g/m^ pro- 

 duced proportionally higher mortalities indi- 

 cating an appi'oximate carrying capacity for this 

 particular culture system (Figure 3). If shrimp 

 were stocked at 40 g/m-, a population of 32 g/m^ 

 remained after 8 weeks. Similarly, when shrimp 



100 



80 



a 60 



3 



40 



20 



4 



WEEKS 



Figure 3. — Mean and standard error for percentage of 

 animals surviving after 8 weeks of growth at three 

 stocking densities. 



were stocked at 80 g/m^, a relatively stable pop- 

 ulation of approximately 52 g/m^ existed during 

 the final 2 weeks of study. Similarly, mortality 

 during the first 8 weeks among a population orig- 

 inally stocked at 160 g/m^ created a population 

 of approximately 80 g/m^, but in this case the 

 survival rate was still declining after 8 weeks of 

 growth. Therefore, a carrying capacity (max- 

 imum biomass obtainable) for this culture sys- 

 tem may have been somewhere between 32 and 

 80 g/m2. 



Although such a carrying capacity would de- 

 pend on the particular culture system, applicable 

 calculations, utilizing data from a laboratory 

 culture study (Subrahmanyam and Oppenhei- 

 mer, 1969) and a pond culture experiment 

 (Broom, 1969), indicate a similar carrying 

 capacity for populations of other systems 

 (ponds, embayments, and laboratory tanks). In 

 the case of the laboratory study, best survival 

 was obtained when shrimp were stocked initially 

 at 34 g/m^, yielding a biomass of 27 g/m^ at the 

 termination of the experiment. Likewise, best 

 survival and an increase in biomass occurred in 

 the pond culture study when initial stocking den- 

 sities were below 20 to 30 g/m^. Recent data 

 from a commercial operator in Central America 

 indicates that, regardless of stocked biomass, the 

 carrying capacity ranged from 5.5 to 7.3 g/m^ 

 (Smitherman and Moss, 1970). Such evidence 

 suggested that final production expectations 

 should be considered in choosing initial stocking 

 densities. 



PRELIMINARY NUTRITIONAL 

 EXPERIMENTS 



A comparison of several groups of diets (Table 

 1) revealed that semipurified diets with casein 

 as the major source of protein (Group I), only 

 produced an average of 18% increase in biomass 

 above stocked biomass levels. Group II, having 

 fish and shrimp meal as additional sources of 

 protein, produced approximately 63% growth on 

 the best diet. Group III diets comparing hydro- 

 lyzed proteins yielded only 39% growth on the 

 best diet, and animals fed at a rate of 15% of 

 their total biomass (Group IV) increased their 

 initial biomass 164%. In addition to increased 



106 



