HOUDE: VITAL RATES. AND ENERGETICS OF MARINE FISH LARVAE 



tional to gross growth efficiency. Required prey 

 of 0.25 ji-g dry weight (the approximate weight of 

 a 100-200 ixm width copepod naupHus) varied 

 more than twentyfold, ranging from 17 to 383 

 d"' among the 10 species (Table 6). Marine 

 fish larvae must ingest 15.3 prey of 0.25 ixg dry 

 weight (15.3 ± 3.9 with 0.95 confidence limit) to 

 attain a 1 |xg increase in dry weight. To the 

 extent that 0.25 |jLg either underestimates or 

 overestimates the mean weight of a prey for a 

 species of fish larva, the required numbers of 

 prey were either overestimated or underes- 

 timated. 



Metabolism 



Weight-specific oxygen uptakes of feeding- 

 stage larvae of 13 species ranged from 0.3 to 44.9 

 p-L/mg/h and increased with temperature. All of 

 the values, except those for haddock, Melano- 

 grattinius aeglefinus, which were considered 

 outUers, were used in the regi'ession describing 

 the relationship between oxygen uptake (Qo,) 

 and temperature (T) (Table 7; Fig. 6). 



Qo, = 2.3973 + 0.2187 T 



r^ = 0.39 Sb = 0.0870. (7) 



The relationship was significant (P = 0.025), but 

 the fit was not as good as those of the other 

 regi-essions. In the 5°-30°C range, Qjo was 1.46, 

 a value lower than that calculated for growth and 

 ingestion rates. 



After rearranging and substituting Equation 

 (1) into Equation (7), an expression between 

 oxygen uptake (Qo.) and gi'owth rate (G) was 

 derived. 



Qo, = 2.2472 + 23.5000 G 



(8) 



From this relationship it can be seen that for 

 gi'owth rate in the sixfold range of 0.05-0.30, 

 oxygen uptake varied only by a factor of 2.7. 



Energy Budgets 



There were substantial effects of temperature 

 on the calculated energy budgets. Weight-spe- 

 cific ingestion rate increased threefold in the 

 10C°-30°C range (Table 8). Numbers of calories 

 increased in all budget components as tempera- 

 ture increased. The relative contributions of 

 each budget component show that growth re- 

 mained constant, a consequence of gross gi'owth 



efficiency being constant over all temperatures, 

 and that relative metabohsm declined at higher 

 temperatures. Assimilation efficiencies declined 

 from 77.1% at 10°C to 59.8% at 30°C. Net gi'owth 

 efficiencies, K2, increased from 37.2% at 10°C to 

 48.1% at 30°C. Fecal energy increased twofold, 

 from 22.9% at 10°C to 40.2% at 30°C. 



DISCUSSION 



Predicted growth and mortality rates of 

 marine fish larvae increase by approximately 

 0.01 per degi'ee in temperature, implying large 

 differences in developmental times and daily 

 probabilities of death in larvae that are hatched 

 in either warm or cold seas. The very high 

 growth and mortahty rates at the high tempera- 

 tures in tropical latitudes indicate fast turnovers 

 of larval populations compared with the longer 

 turnover times expected in temperate seas. In 

 reviewing mortality of marine organisms in rela- 

 tion to their size, Peterson and Wroblewski 

 (1984) and McGurk (1986) noted the exception- 

 ally high mortality rates of marine fish eggs and 

 larvae and discussed some probable reasons and 

 consequences. McGurk (1986) believed that 

 patchiness and susceptibility to predation ex- 

 plained the relatively high rates of mortality. 

 The analyses presented here demonstrate that 

 the rates not only are high but that they vary 

 predictably with temperature. Based on the 

 species that are represented, the results are 

 presumed to represent a latitudinal trend as well 

 as to be seasonally significant. More than four- 

 fold differences in the expected mortality rates 

 of marine fish larvae can be attributed to envi- 

 ronmental temperature, without considering ef- 

 fects of larval size, in the 5°-30°C range. Ex- 

 pected weight-specific growth rates of fish 

 larvae also were demonstrated to be six times 

 higher at temperatures in tropical seas (30°C) 

 than at temperatures in cold seas (5°C). 



A consequence of declining temperature is an 

 exponential increase in predicted larval stage 

 duration (Fig. 2). Stage durations for larvae that 

 develop at <8°C exceed 100 days, while larvae 

 that develop at the 25°-30°C temperatures in 

 tropical seas, metamorphose in <30 days. More 

 importantly, there is a relatively large increase 

 in its potential variabihty as stage duration in- 

 creases. The highest variability in gi'owth rate is 

 observed in species that develop at high tem- 

 perature (Fig. 1), but the highest variability in 

 stage duration is observed at low temperature. 

 Consequently, small changes in growth rate can 



485 



