o 

 > 



cr> 



Ld 



2- 



LARVAL SEABASS 







4 6 8 10 2 4 



DRY WEIGHT (mg- larva"') 



Figure 5. — Relations of protein (upper) and DNA (lower) to dry weight for laboratory-reared larval grunion (left) 



and white seabass (right). 



This may reflect differences in the Hfespans and 

 metabolic rates; grunion are small fish, reaching 

 maturity in a year and living less than 5 years 

 (Frey 1971), while seabass and halibut grow to 

 very much larger size and can live more than 20 

 years (Frey 1971; Thomas 1968). 



Figure 7 shows the variability in the amount of 

 lipofuscin in larvae of the same age. At time "0", 

 all fish were newly hatched. The variance was 

 low in the first few days, but increased dramati- 

 cally with time because larvae within each tub 

 grew (and, presumably, respired) at very different 

 rates. There were differences in averages between 

 high food and low food conditions, and between 

 experiments (Table 2), but the variance in dry 

 weight, protein, DNA, or lipofuscin was so large 

 that the overlap obscured any differences be- 

 tween conditions of rearing. 



Grunion and halibut larvae start life with 

 greater concentrations of lipofuscin than do sea- 



bass, and though the concentration decreases 

 rapidly as grunion and halibut age (Fig. 8), they 

 still have almost a 10-fold greater concentration 

 than do larval seabass when all are 20 days old. 

 All three species increased in weight faster than 

 they increased in lipofuscin, so the concentration 

 of lipofuscin was "diluted" by growth. Because 

 protein was a constant fraction of dry weight 

 (Fig. 5, upper), this dilution was not due to skele- 

 tal growth alone. If the rate of weight-specific 

 growth exceeds the rate of weight-specific respi- 

 ration during early life, the concentration of lipo- 

 fuscin should decrease, as observed, and only 

 when growth ceases or slows considerably should 

 lipofuscin accumulate relative to weight. Alter- 

 natively, lipofuscin could change chemically with 

 time, becoming more difficult to extract (Vernet 

 et al. 1988), so that the rate of accumulation of 

 lipofuscin would be underestimated. 

 We attempted to stop growth by starving the 



412 



