MARGULIES: EFFECTS OF FOOD AND TEMPERATURE ON WHITE PERCH 



+ bt, where L, is length at time "t" days and b is 

 daily growth rate (mm per day). Growth in weight 

 for the 8 d period was determined from the expo- 

 nential regression of dry weight on days after first- 

 feeding: Wi = W^e^', where Wt = dry weight at 

 time "f days, G = instantaneous daily growth coef- 

 ficient, and Wq = dry weight at first-feeding. Spe- 

 cific growth rate (percent per day) was calculated 

 as 100(e'" - 1). In addition, mean incremental 

 growth coefficients (i.e., between sampling days 2, 

 4, 6, and 8) also were calculated (Ricker 1975). 



Data were analyzed by regression analysis, anal- 

 ysis of variance (ANOVA), and analysis of covari- 

 ance (ANCOVA) followed by the Student-Newman- 

 Kuels (SNK) multiple comparison test (Sokal and 

 Rohlf 1981). The probability level for rejecting null 

 hypotheses was P = 0.05. 



RESULTS 



Development 



Preserved white perch eggs ranged from 0.76 to 

 1.03 mm in diameter. Mean diameters of eggs 

 hatched at 13°, 17°, and 21°C were 0.91, 0.87, and 



Table 1. — Characteristics of fertilized wfiite perch eggs, newly 

 hatched larvae and first-feeding larvae cultured at three temper- 

 atures. 



0.92 mm, respectively (Table 1). Each egg contained 

 a large volume of yolk (0.14-0.16 mm^), and a 

 prominent, amber-colored oil globule (0.0070- 

 0.0081 mm'). There were no significant differences 

 (ANOVA, P > 0.10) among incubation temperatures 

 for mean egg diameter, yolk volume, or oil globule 

 volume (Table 1). 



Mean larval size at hatch ranged from 2.37 to 2.81 

 mm SL and averaged 2.50 mm (Table 1). Dry weight 

 of hatchlings was approximately 35 j^g. Newly 

 hatched larvae had unpigmented eyes, with the head 

 deflected downward over the yolk sac. Mean lengths 

 and weights of newly hatched larvae at the three 

 temperatures did not differ significantly (ANOVA, 

 P > 0.10). 



At the first-feeding stage, larvae averaged 3.45 

 mm SL and weighed approximately 19 ^ig (Table 1). 

 First-feeding larvae had utOized at least 98% of their 

 yolk reserves and from 55 to 75% of their oil. At 

 the first-feeding stage no significant temperature 

 effects were apparent for size of larvae, percentage 

 of yolk remaining or percentage of oil volume re- 

 maining (ANOVA, P > 0.10). Although not signifi- 

 cant, there was a trend for larvae to retain more 

 yolk and oil at lower temperatures. 



Temperature had a pronounced effect on the dura- 

 tion of the egg and yolk-sac larval stages (Fig. 1). 

 The relationships between the durations of these 

 stages and temperature were best described by 

 decreasing exponential functions. Although effect 

 of temperature on hatching success was not mea- 

 sured precisely, rough estimates based on removals 

 of dead eggs were made. Percentage hatch was near 

 80% at 13°C, approximately 60% at 17° C, and near 

 20% at 21°C. 



Survival 



Expected survival after 8 days of feeding ranged 

 from 4.0 to 55.0%, depending on temperature and 

 food conditions (Fig. 2). As expected, survival at 

 each temperature was highest for the well-fed lar- 

 vae in food group 1. Larvae fed at low food levels 

 for as little as 2 days (groups 2, 3, and 4) exhibited 

 significantly reduced survival at all temperatures 

 (ANOVA and SNK procedure, P < 0.05). In par- 

 ticular, larvae fed at low food concentrations for 4-8 

 days (groups 3 and 4) displayed markedly reduced 

 survival at 17° and 21°C. 



Growth 



At 13°C, grovrth in length was slow under all food 

 conditions— all larvae were <4.0 mm SL after 8 days 



65 



