MAY: EFFECTS OF DELAYED INITIAL FEEDING 



(Omori, 1970) , the values given here for larvae 

 1 and 4 days old, which had been preserved in 

 Formalin to allow removal of yolk by dissection, 

 may be somewhat in error. 



The level of protein in larval samples was esti- 

 mated by multiplying the nitrogen level by 6.25 

 (White, Handler, and Smith, 1968) , and fat was 

 calculated by difference: 100 - (percent ash + 

 percent protein) = percent fat. Nonprotein 

 nitrogen and carbohydrate were assumed to be 

 present in negligible amounts in this material 

 (Lasker, 1962). Caloric content was calculated 

 by multiplying weights of fat and protein in 

 average larvae by 9.5 cal/mg and 5.7 cal/mg, 

 respectively (Brody, 1945; Kleiber, 1961). 

 Table 7 lists the resulting values. The most 



Table 7. — Protein, fat, and caloric content of larval 

 samples. Protein and fat are given as percentages of 

 total dry weight. Protein was calculated from the nitro- 

 gen content of samples, fat by difference, and caloric 

 content by multiplying weights of protein and fat by 

 standard conversion factors. 



notable trends are an increase in protein level 

 and decrease in fat level, in both fed and unfed 

 larvae (Table 7). Unfed larvae had lower fat 

 and about the same or somewhat higher pro- 

 tein levels than fed larvae. Among 20-day-old 

 larvae, those for which initial feeding had been 

 delayed tended to have higher fat and lower 

 protein levels than those fed early (Table 7). 

 Reflecting changes in proximate composition. 



the caloric content of larval tissue showed an 

 early decrease and from day 10 on showed no 

 increasing or decreasing trend, in both fed and 

 unfed larvae (Table 7). From day 10 on, 

 starved larvae tended to have a lower caloric 

 content than fed larvae. The caloric contents 

 of 20-day-old larvae showed no consistent trend 

 with time of initial feeding (Table 7). 



DISCUSSION 



The developmental process requires a nutri- 

 tional input to supply energy and raw materials. 

 In larval grunion which receive no food, devel- 

 opment does not progress beyond the stage 

 reached when the yolk is absorbed, although the 

 larvae survive well beyond this point. The pro- 

 cess of ossification is halted and the upward 

 flexion of the notochord does not take place in 

 unfed larvae, while tissue resorption, supplying 

 energy for metabolic processes during starva- 

 tion, results in a slow decrease in larval mass. 

 Fat seems to be utilized most during starvation. 

 The amount of fat in an average starving larva 

 decreases by 0.071 mg, or 0.689 cal, during 16 

 days of starvation, while protein decreases by 

 only 0.043 mg, or 0.245 cal (Tables 2 and 7). 

 The fat and protein levels of feeding larvae are 

 not greatly diff"erent from those of starving lar- 

 vae (Table 7), but in the former case the ob- 

 served increase in protein level with time must 

 be a consequence of rapid protein synthesis in 

 the growing organism, whereas in the latter it 

 reflects the utilization of the body's fat reserves. 



When food is off'ered to unfed larvae, growth 

 begins and proceeds at about the same rate as 

 in larvae fed from day 1 (Figure 2). Weight 

 and body composition at day 20 in larvae whose 

 initial feeding was delayed for various periods 

 is close to that of larvae fed for similar lengths 

 of time from day 1 (Tables 2, 3, and 7), though 

 fat is much more depleted in larvae fed for 4 

 and 7 days starting on days 16 and 13, respec- 

 tively, than in larvae fed for 4 and 7 days start- 

 ing on day 1. Larvae fed for a period of 16 

 days, from day 4 to day 20, gained more weight 

 and had higher protein levels than larvae fed 

 from days 1 to 16 (Tables 2, 3, and 7) , suggesting 

 that a few days' delay in initial feeding caused 



421 



