MARGULIES: EFFECTS OF FOOD AND TEMPERATURE ON WHITE PERCH 





 O 



'S 

 o 

 o 



o 



2 4 6 8 



Days after First Feeding Stage 



Figure 5.— Mean instantaneous growth coefficients attained by 

 white perch larvae at 2 d intervals. Error bars are ±2 SE. 



DISCUSSION 



White perch produce large numbers of eggs, hatch 

 at small sizes (<3 mm) and undergo pronounced dif- 

 ferences in development, growth, and survival in 

 relation to variable food and temperature conditions. 

 Egg stage duration decreased by a factor of three 

 over the temperature range of 13°-21°C, but the 

 reduced diu-ation at higher temperatures was off- 

 set by a decline in percent hatch of nearly 60%. 

 Morgan and Rasin (1982) reported that optimum 

 hatch of white perch eggs in the laboratory occurred 



at 14°-16°C, and believed that greater percent 

 hatch occurred in the estuary at these temperatures. 

 Hardy (1978) reported that peak spawning activity 

 for Chesapeake Bay white perch occurs at 12°- 

 16°C. My results indicate that optimum tempera- 

 tures for hatch occur at <17°C. 



The effect of temperature on yolk-sac stage dura- 

 tion may be important. Prolongation of this stage 

 could have significant effects on cohort survival. 

 Predation by planktivorous fishes on yolk-sac larvae 

 is probably substantial in tidal freshwaters, based 

 on the results of laboratory predation experiments 

 (Margulies 1986). Results reported here indicate that 

 a short-term decrease in temperature of 4°C dur- 

 ing the spawning season, which is not unusual in 

 tidal freshwaters (James et al. 1984^), could prolong 

 the yolk-sac stage by at least 3 days, which could 



^James, R. W, , R. H. Simmons, and B. F. Strain. 1984. Water 

 resources data. Maryland and Delaware, Water Year 1983. U.S. 

 Geol. Surv. Water-Data Rep. MD-DE-83-1. 



c 



0} 



(U 



o 

 o 



5 



o 



5 



3 



o 



0) 



c 



CO 



c 

 (0 



(0 



c 



0.20 



0.16 



0.12 



0.08 



0.04 



• Group 1 Y = 0.0187T - 0.1882 {r^=.98) 



OGioup 2 V • 0.013?r - 0.14r,5 li^=.961 



A Group 3 Y = 0.0043T - 0.0376 (r^=.97) 



AGroup 4 Y = O.OOllT - 0.0091 li^=.9^) 



- / 



o 



— a' 



13 17 



Temperature(°C) 



21 



FiGLTRE 6.— Relationship between temperature and instan- 

 taneous growth coefficient for each food group. 



69 



