HOUDE; VITAL RATES. AND ENERGETICS OF MARINE FISH LARVAE 



increases in Z also were determined at those 

 three temperatures. 



Growth Efficiency 



Gross growth efficiency (A'l) is the proportion 

 of ingestion that goes to growth; 



K, = G/I , 



where G is the weight-specific gi'owth rate and / 

 is the weight-specific ingestion rate. Growth 

 efficiencies and temperatures (T) in published re- 

 ports were examined. An attempt was made to 

 fit a linear regi-ession to midpoints of A'j re- 

 gressed on midpoints of T for species where data 

 were available. 



Because / = G/A'i and the regi'ession relation- 

 ship between G and T had been defined, weight- 

 specific ingestion rate also could be related to 

 temperature. That expression was applied to 

 estimate the weight-specific ingestion rate re- 

 quired to attain mean, among-species gi'owth 

 rates in relation to temperature. It was assumed 

 that an average food particle for a first-feeding 

 larva weighed 0.25 ixg dry weight. Then, the 

 number of particles required to attain average 

 growth rate and the consequences of changes in 

 temperature on that requirement were ex- 

 plored. The regi'ession relationship between / 

 and G also was examined to determine the rate 

 of increase in ingestion necessary to support 

 increased gi'owth. 



Metabolism 



The Qo.., i.e., weight-specific oxygen uptakes, 

 were obtained for marine fish larvae where data 

 were available. Values were taken directly from 

 literature or derived if the relationship between 

 oxygen uptake and larval dry weight was re- 

 ported. Values used here were confined to those 

 for feeding or end-of-yolk-sac stage larvae. The 

 midpoints in the range of Qo, for a species were 

 regressed on the midpoints of the temperature 

 values to obtain a relationship between weight- 

 specific oxygen uptake and temperature. A Qio 

 was derived from the predicted values of Qo in 

 the 5°-30°C range. 



Energy Budgets 



Energy budgets for average first-feeding 

 larvae at 10°, 20°, and 30°C were developed from 

 the information and relationships on growth 



rates (G), oxygen uptake (Qo,), and ingestions 

 (/). Budgets were expressed as 



I = G + M + F 



where M is metabolism and F is feces. The Qo., 

 was converted to M using an oxycalorific equiv- 

 alent of 0.00463 cal/|jiL 0^ (Brett and Groves 

 1979). The oxygen uptake estimates reported in 

 the literature generally were made on "resting" 

 or anesthetized larvae. These estimates were 

 presumed to represent routine metabolism. For 

 the energy budgets, the reported Qo, values 

 were multiplied by 2.0 to estimate active metab- 

 olism for 12 hours of the day, the time that a 

 larva was assumed to swim actively while feed- 

 ing (i.e., daylight hours). The estimated Qq^ 

 from the regi'ession relationship was assumed to 

 apply during the remaining 12 hours. The 2.0 

 multipher is commonly used, but may be conser- 

 vative (Brett and Groves 1979). If metabolism 

 has been underestimated, the absolute values of 

 budget components are in error but relative ef- 

 fects of temperature on the larval energy 

 budgets still will be expressed. 



Both ingestion rates and gi'owth rates were 

 converted from dry weight to calories by assum- 

 ing an equivalency of 5,000 cal/g dry weight. 

 Values for feces in the energy budgets were 

 obtained by difference. Energy budgets were 

 expressed both in absolute and relative (i.e., 

 percent) terms. After the energy budgets had 

 been determined, assimilation efficiencies, A = 

 (G + M)/I, and net growth efficiencies, K-z = 

 GI(G + M), were derived and compared among 

 temperatures (see Table 8). 



RESULTS 



Growth 



Weight-specific growth coefficients ranged 

 from <0.01 to >0.55, indicating a widely varying 

 potential for gi'owth among species of marine 

 fish larvae that was strongly related to tempera- 

 ture and, presumably, latitude (Table 2; Fig. 1). 

 Relative growth-in-weight ranged from <\% to 

 >73'7f d~^ The regression of midpoint G on 

 midpoint T for 27 species indicated an approxi- 

 mate 0.01 increase in G for each degree increase 

 InT. 



G = -0.0036 + 0.0094 T 



r'~ = 0.57 Sb = 0.0016. (1) 



473 



