LAURENCE: BIOENERGETIC MODEL FOR WINTER FLOUNDER LARVAE 



tempted to feed constantly under daylight condi- 

 tions and ceased feeding entirely during darkness. 

 Evacuation rates of the gut while larvae were 

 actively feeding were recorded at 8°C for estimates 

 of digestion rates. Results of 10 individual larvae 

 showed a mean, active digestion time of 6.6 h with 

 a range of 5.1-8.4 h. 



Effects of Prey Density on 

 Growth and Survival 



The effects of five prey densities from 0.068 to 

 20.5 cal/liter (approximately 0.01-3.0 nauplii/ml) 

 on growth and survival of winter flounder larvae 

 from hatching to metamorphosis at 8°C were 

 examined. Larval survival did not exceed 2 wk at 

 the lower two densities of 0.01 and 0.1 nauplius/ 

 ml. Growth expressed as dry weight against time 

 at the three survival densities (3.4, 6.8, and 20.5 

 cal/liter) was similar (Figure 3), as indicated by 

 the confidence intervals about the slopes of the 

 descriptive regression equations (Table 2). Spe- 



J 100. 



20 5 CA L/l 



3 4 C A I / 1 



0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 

 NEEKS AFTER YOLK ABSORPTION 



8.0 9.0 



FIGURE 3.— Growth of winter flounder larvae at 8°C and at 

 three different planktonic prey densities. 



TABLE 2. — Regression equations and statistical parameters of 

 winter flounder dry weight growth vs. time at 8°C and different 

 planktonic prey densities. 



cific growth rates on a daily basis increased with 

 plankton concentration and were experimentally 

 observed to be 8.62%/day for 3.0 nauplii/ml, 

 7.68%/day for 1.0 nauplius/ml, and 5.72%/day for 

 0.5 nauplius/ml. 



Plankton density influenced survival more sig- 

 nificantly than growth. Specific mortality coeffi- 

 cients calculated by the methods of Laurence 

 (1974), which correct for the number of experi- 

 mental removals for growth measurements, dem- 

 onstrated a direct relationship with lower mor- 

 tality rates at each higher plankton density (Table 

 3). Plots of predicted specific mortality coefficients 

 through the range of plankton densities from 0.68 

 to 20.5 cal/liter based on the above results yielded 

 an exponential relationship (Figure 4). 



TABLE 3. — Daily mortality coefficients of winter flounder at8°C 

 as influenced by planktonic prey density. 



'No calculable survival at the lowest plankton density of 0.068 cal/liter. 



0.0 1.5 3.0 



7.5 9.0 10.5 12.0 13.5 15.0 19.5 19.0 19.5 7 1.0 

 PLANKTON CONCENTRATION tCAL/LHRE) 



FIGURE 4. — Daily mortality coefficients of winter flounder at 

 8°C from the period hatching to metamorphosis as influenced 

 by prey density. 



Metabolic Rate 



Laurence (1975) expressed metabolism of 

 winter flounder from hatching through meta- 

 morphosis in terms of oxygen consumption. 

 Regression relationships of mean hourly oxygen 



533 



