FISHERY BULLETIN: VOL. 70, NO. 1 



buildup of anaerobic conditions. Division of 

 tank bottoms into sundry tunnels and levels was 

 created by specific placement of bricks and clay 

 drain tiles. 



AERATION STUDY 



Aeration provided by jetting streams of fil- 

 tered seawater into respective tanks was com- 

 pared to aeration supplied by bubbling air 

 through airstones into tanks in which water was 

 continuously added with no agitation of the water 

 column for an 8-week period. Two airstones 

 were placed in each tank and valve-regulated 

 air lines controlled the pressure at approximately 

 4 psi. Oxygen levels were monitored periodically 

 and used along with survival rates as a basis for 

 evaluation of replicate groups aerated by each 

 method. 



STOCKING DENSITY STUDY 



Survival data were compared among triplicate 

 tanks stocked at 10, 20, and 40 shrimp per m^ 

 for an 8-week period. These densities of ap- 

 proximately 40, 80, and 160 g/m- were chosen 

 on the basis of data provided in pond and lab- 

 oratory culture of penaeid shrimp (Broom, 1969; 

 Subrahmanyam and Oppenheimer, 1969). 



PRELIMINARY NUTRITIONAL STUDY 



Triplicate groups of ten 4 g brown shrimp 

 (P. aztecus) were fed a series of pelleted diets. 

 Growth data (biomass increase) was used as a 

 means of evaluation. Diets examined consisted 

 of those patterned after Japanese purified diets 

 (i.e., diets containing only chemical ingredients) 

 (Table 1, Group I) (Diet 1 was conducted for 5 

 weeks and Diets 2, 3, and 4 for 11 weeks each) ; 

 a second group of semipurified diets (i.e., con- 

 taining defined chemical ingredients but contain- 

 ing one or more natural products) providing four 

 combinations of levels of protein, fat, shrimp, 

 and fish meal (Group II) (conducted for 11 

 weeks) ; and a third group designed to compare 

 the nutritional value of casein, yeast, and soy 

 hydroly.sates (Group III) (conducted for 6 

 weeks). All of these groups were fed at 5% 



Table 2. — Percent of pellet dissolved over time and at 

 at three concentrations of binder. (Values are means 

 and standard deviation on two replicates with Diet 1.) 



of their respective biomass daily. In addition, 

 Diet 6 was fed at 5, 10, and 15% of biomass 

 (Group IV) (conducted for 6 weeks). 



Combined environmental factors which pro- 

 duced best survival in each of the environmental 

 experiments (i.e., culture conditions consisting 

 of bare fiber glass tank bottoms, supplied aera- 

 tion, and a stocking density of approximately 

 40 g/m-) were used in all nutritional studies. 

 This combination oflfered a maximum potential 

 for an increase in biomass and therefore allowed 

 accurate evaluation of diflferences among diets 

 tested. Although survival in bare fiber glass 

 tanks was not significantly different from sand 

 substrates, the fact that bare tanks were simpler 

 to maintain dictated that they be used for the 

 nutritional studies. 



Prior to starting nutritional studies, the phys- 

 ical properties of pelleted diets were evaluated 

 for acceptability as shrimp food. Pellet consis- 

 tency was determined according to its ability to 

 resist dissolution over a given period of time, 

 and texture and size were chosen according to 

 animal performance when presented several 

 choices. Collagen' proved to be a suitable bind- 

 ing agent. Using an experimental design with 

 time and collagen levels as variables, a pellet 

 with 5% collagen added as a binder was found 

 to offer optimum consistency over a 24-hr im- 

 mersion in salt water (Table 2). Percent dis- 

 solution was measured by taking dry weights 

 after 6, 12, and 24 hr of immersion (no shatter- 

 ing of pellets was observed, and all loss of weight 

 was therefore assumed to be from dissolution). 

 Animals were observed to feed most readily on 



* Supplied on an experimental basis by the Hides and 

 Leather Division of the U.S. Department of Agriculture 

 Eastern Utilization Laboratory in Philadelphia, Pa. 



104 



