Table 5.- Water condition on selected dates. 



tanks. At the time of weekly cleaning, the water in 

 the nursery tanks was poured through the sieve 

 also described under Aquarium Tanks. Any fish 

 remaining on the sieve were placed back in the 

 adult tanks. 



Fish were counted and weighed weekly during 

 periods 0-71. During periods 71-124, this was done 

 only at the approximate brood intervals of the fish, 

 which were 3 wk for the guppy and 4 wk for the 

 swordtail. Fish were counted simply by netting 

 them from one container to another. Counts were 

 categorized into "immature" (those whose sex 

 could not be determined from external inspection), 

 male, and female. Fry and juveniles were counted 

 when moved between adult and nursery tanks. 

 Dead fish found in tanks were recorded as mor- 

 talities. 



Exploitation was done at the time of counting. 

 To apply an exploitation rate of 1//;, each »th fish 

 was removed (n was always an integer). This was 

 applied equally to juveniles and adults, but not at 

 all to fish in the nursery tanks. 



Population and catch weights were also deter- 

 mined at the time of counting. Fish were drained 

 and placed in a previously weighed container of 

 water. Total weight was measured and fish weight 

 obtained by subtracting the tare. 



FISHERY BULLETIN: VOL. 73, NO. 4 



COURSE OF POPULATIONS 



Independent Populations 



Although chronologically the competing 

 populations preceded the independent popula- 

 tions, the more logical order of presentation is to 

 deal with the independent populations first. This 

 arrangement will be followed in the remainder of 

 the report. 



Separate populations of guppies and swordtails 

 were started on 19 May 1970 (3-wk period No. 79). 

 Each of these was permitted to grow for an initial 

 period of about 1 yr (Figures 2, 3) before exploita- 

 tion was begun. Even though complete 

 equilibrium had not been reached, exploitation 

 was started at 25% per brood interval (3 wk) for 

 the guppy and 10% per interval (4 wk) for the 

 swordtail. The lower rate for the swordtail was 

 based on previous experience showing lower 

 productivity for that species. Initial rates were 

 maintained during weeks 289-334 for the guppy 

 and 290-334 for the swordtail. Final rates were 

 33.3% for the guppy (weeks 337-373) and 16.7% for 

 the swordtail (weeks 338-374). Responses were in 

 accord with expectations for the guppy (Figure 2) 

 and the early swordtail history, but there was an 

 increase in both number and weight in the sword- 

 tail in the last five brood intervals (Figure 3). This 

 anomaly will be discussed under "Oscillatory 

 Fluctuation." 



320 

 ^80- 

 240- 

 200 



X 

 tn 



"- I SO- 

 LI. 

 O 



a, '20- 



OD 



2 80- 



Z) 



-z 



40- 



i5 

 30- 



_ 25- 



E 



° 20 



i 15- 



g lOH 



5 



0- 

 WEEK 



3^«eek period 80 



240 



110 



Figure 2.-Course of independent guppy population. Numbers 

 indicate target exploitation rates. 



876 



