perimental path. Weeks 0-36, which included 

 original mixed species populations and subse- 

 quent unexpected behavior of single species pop- 

 ulations, may be regarded as exploratory in nature 

 and have been designated Phase I. The test of the 

 juvenile-fry interaction hypothesis, during weeks 

 36-58, may be considered confirmatory in nature 

 and has been designated Phase II. The logic of the 

 experimental path is depicted in Figure 2. Experi- 

 mental observations collected during Phase I were 

 indeed responsible for the development of the 

 juvenile-fry hypothesis tested during Phase II. 



EXPERIMENTAL PATH 



1. Mixed species stock- recruitment 



relations , . 



(platy mortality) 



2. Single species stock -recruitment 

 analysis 



( juvenlle-f ry Interaction?) 



WEEKS DESIGNATION 



0-8 



PHASE I 



8-36 



3. Test of juvenile-fry 

 Interaction hypottiesis 



Retention of 



long-term 



controls 



36- 58 



PHASE II 



Figure 2. — The experimental design for guppy and southern 

 platyfish (platy) populations. 



Phase I (Weeks 0-36) 



WEEKS 0-8. — Twelve experimental aquaria 

 were grouped into three blocks of four aquaria 

 each and each block was assumed to have equal 

 position effect (Figure 3). Blocks A and C con- 

 tained replicate groups of four mixed species 

 populations each. Block B had replicate single 

 species guppy populations (aquaria 5 and 6) and 

 platy populations (aquaria 7 and 8). A gold strain 

 of guppies was used to allow visual separation of 



•BLOCK A 



timer 



6 



FISHERY BULLETIN: VOL. 78, NO. 3 

 BLOCK B y-BLOCK C' 



4 5 6 



8 9 



10 

 11 

 12 



timer 



 



yk 



mttmmitiiMmim 



I [♦heater 



•♦balance 



FIGURE 3. — Schematic of the laboratory facility showing block- 

 ing of experimental aquaria for guppy and southern platyfish 

 populations. 



guppy and platy fry at birth, otherwise difficult 

 with wild-type strains. Weights, sex, and numbers 

 of each species initially stocked in aquaria are 

 listed in Table 2. Estimated age of both guppies 

 and platies at stocking was 14-18 wk. 



All populations were fed rations containing 

 approximately equal proportions of the food items 

 with the exception of Artemia nauplii. All popula- 

 tions received a fixed daily ration of Artemia 

 nauplii, 0.2 g. Total rations were increased in 

 stepwise increments to keep the daily wet weight 

 equivalent of rations at from 25 to 359c of total 

 population biomass. Since growth of guppies ap- 

 peared more rapid in mixed species populations, 

 single species population rations were increased 

 in rapid increments at the end of week 6. Food 

 rations supplied to populations during the first 8 

 wk are in Table 3. At the end of week 8 all platies 

 were removed from mixed species populations and 



Table 2. — Stocking of guppies and southern platyfish at initiation of experiments, 5 June 



1975. Weights (grams) in parentheses. 



560 



