HOWELL: TEMPERATURE EFFECTS ON YELLOWTAIL FLOUNDER 



yolk-sac volume (cubic millimeters) then was mul- 

 tiplied by the calculated ash-free dry weight of a 

 cubic millimeter of yolk to yield the ash-free dry 

 weight of the yolk within the yolk sac. This value 

 was subtracted from the predicted ash-free dry 

 weight of the yolk-sac larvae to give the ash-free 

 dry weight of the larval tissue alone. The validity 

 of using the same ash-free dry weight (and caloric 

 value) of yolk throughout the yolk-sac stage has 

 been demonstrated by Lasker ( 1962). 



Temperature effects on yolk utilization rate 

 were determined using analysis of covariance to 

 compare the slopes of the regression lines. The 

 relationship between larval notochord length and 

 hours posthatch was nonlinear. Growth curves, 

 linearized by logarithmic (natural) transforma- 

 tion of the time axis (hours posthatch), were com- 

 pared by analysis of covariance. Notochord 

 lengths, ash-free dry weights of yolk-sac larvae, 

 and yolk-sac volumes at time of hatching and 

 yolk-sac absorption for the four different tempera- 

 tures were compared using analysis of variance. 

 Where significant differences were found, the 

 Student-Newman-Keuls (SNK) test was used to 

 locate individual treatment differences. 



Caloric values of yolk and larval tissue were 

 determined by wet oxidation following Maciolek 

 (1962). Ten samples of unfertilized ova were used 

 to determine the caloric content of yolk. Caloric 

 content of larval tissue was determined from 

 finely ground samples of larvae after total yolk 

 absorption. Three samples each were done from 



Table l. — Summary of size, ash-free dry weight (AFDW), and 

 caloric value of unfertilized yellowtail flounder eggs. 



larvae reared at 8° and 12° C. No calorimetry was 

 attempted at 4° and 10° C since insufficient num- 

 bers of larvae were available at yolk-sac absorp- 

 tion. 



Yolk utilization efficiency, expressed as a per- 

 centage, is defined as the ash-free dry weight of the 

 larva minus its yolk (or its caloric equivalent) at 

 time t, divided by the ash-free dry weight of yolk 

 (or its caloric equivalent) that had been used from 

 fertilization to time t. Details of this method are 

 described elsewhere (Toetz 1966; Laurence 1969). 

 Because variability was high in ash-free dry 

 weight measurements, it was not possible to calcu- 

 late meaningful daily efficiencies. Thus efficien- 

 cies were calculated at ony two points in time — at 

 hatching and at yolk-sac absorption. Efficiencies 

 also were calculated using ash-free dry weights of 

 larvae minus their yolk sacs and ash-free dry 

 weights of yolk utilized, as predicted by linear 

 regressions. These values were used to examine 

 trends in efficiency over time. 



RESULTS 



Data on size, ash-free dry weight, and caloric 

 value of unfertilized eggs from the females used in 

 this study are given in Table 1. The mean egg 

 diameter (0.75 mm) is slightly smaller than the 

 mean diameters of 0.9 and 0.88 mm reported by 

 Bigelow and Schroeder (1953) and Colton and 

 Marak.3 



Incubation temperature affected both the 

 length and weight of yolk-sac larvae at time of 

 hatching, but not at yolk-sac absorption (Table 2). 

 At hatching, notochord length was significantly 

 longer in larvae incubated at 8° and 10° C than in 

 those incubated at 12° and 4° C (ANOVA, SNK, 

 P<0.05). Among the four temperatures, no sig- 

 nificant differences ( ANOVA, P>0.05) were found 

 between ash-free dry weights of entire yolk-sac 



'Since the mean was derived by subtraction, no sample size or standard 

 deviation are given. 



^Colton.J. B. Jr.andR. R. Marak. 1969. Guide for identify- 

 ing the common planktonic fish eggs and larvae of Continental 

 Shelf waters. Cape Sable to Block Island. U.S. Bur. Commer. 

 Fish., Biol. Lab., Woods Hole, Mass., Lab. Ref 69-9, 43 p. 



Table 2. — Mean ± standard deviation of lengths, ash-free dry weights, and yolk-sac volume of yellowtail flounder reared at 

 four temperatures. Values connected by vertical lines are not significantly different (ANOVA. SNK,P>0.05). 



At yolk-sac absorption 



Tempera- 

 ture (" C) 



Sample 

 size 



Notochord length 

 (mm) at hatching 



At hatching 



Yolk-sac 

 volume (mm^) 



Ash-free dry weight of 

 yolk-sac larvae (mg) 



0.0086 = 0.001 

 ,0116=0 002 

 .0100 = 0.002 

 .0119 = 0.002 



Ash-free dry weight of 

 yolk-sac larvae (mg) 



0.0040 = 0.001 

 .0043=0.001 

 0042 = 0.001 



Notochord 

 length (mm) 



3.458=0,218 

 3.542 = 0,189 

 3,406=0.190 



733 



