FISHERY BULLETIN: VOL. 80, NO. 3 



bioenergetics was selected as our approach be- 

 cause it represents these functions in an inte- 

 grated and comprehensive fashion. 



Bioenergetics of adult fishes has been studied 

 for some time (Ivlev 1939a, b; Winberg 1956; 

 Warren and Davis 1967; Brett and Groves 1979). 

 As interest in fish eggs and larvae grew, knowl- 

 edge gained from studies of adults was applied 

 toward research on early life stage energetics 

 (Toetz 1966; Laurence 1969, 1971, 1977; Cooney 

 1973). Most of these publications are concerned 

 with the critical period when larvae begin active 

 feeding and change from endogenous to exoge- 

 nous energy sources (May 1974b). Other re- 

 searchers have used bioenergetic studies to 

 assess the effects of pollutants or other environ- 

 mental conditions on larvae (Laurence 1973; 

 Eldridge et al. 1977). 



Our early research on striped bass embryos 

 and larvae has already been reported (Eldridge 

 et al. 1981). Emphasis was on factors associated 

 with food and feeding of larvae and how they re- 

 lated to mortality, point of no return, develop- 

 ment, and, to a limited extent, energetics. The 

 research presented here is a detailed analysis of 

 the energy sources, endogenous and exogenous, 

 and their influence on energy outputs in the early 

 life stages of striped bass. 



MATERIALS AND METHODS 



Energy Input Determinations 



Component analyses of eggs prior to fertiliza- 

 tion were done on eggs from seven different fe- 

 males used for embryo and larval studies and on 

 34 ripe fish collected at random from natural 

 spawning areas. All eggs came from fish from 

 the Sacramento River, Calif. Three replicates of 

 25 eggs each were weighed fresh after brief blot- 

 ting on absorbent filter paper, then dried to con- 

 stant weights at 60°C and reweighed to yield 

 water contents and total dry weights. Yolks and 

 chorions were dissected from Formalin 3 -pre- 

 served eggs with microdissection tools; they then 

 were dried and weighed to the nearest 0.1 ng. 

 These amounts were then subtracted from the 

 total weight to provide oil weights. Total lipid 

 contents were obtained by 2:1 chloroform-meth- 

 anol extraction in micro-Sohxlet apparatus. Our 

 procedure for caloric determinations of yolk and 



'Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



oil involved whole egg homogenization followed 

 by centrifugation to separate yolk, oil, and chor- 

 ion membrane components. Yolk and oil were 

 then aspirated into dishes, oven dried to constant 

 weights at 60°C, and bombed according to stan- 

 dard microbomb calorimetric methods. Esti- 

 mates of tissue and Artemia caloric contents 

 were made from homogenates of whole animals, 

 the larvae being sampled after complete oil glob- 

 ule consumption. All caloric contents are ex- 

 pressed as calories per gram ash-free dry 

 weight. 



All measurements of yolk and oil volume and 

 lengths were done with ocular micrometers in 

 dissecting microscopes. All measurements and 

 determinations were performed at least in dupli- 

 cate and, if possible, in triplicate. 



Eggs from seven different females were fertil- 

 ized artificially according to methods of Bonn et 

 al. (1976). Eggs were incubated in McDonald 

 jars. After hatching, larvae were transferred to 

 hemispherical 8 1 acrylic plastic containers held 

 in water tables to stabilize temperature. Initial 

 stocking densities were approximately 150 lar- 

 vae/container. In three of the seven batches, lar- 

 vae were reared to the age when feeding begins, 

 7 d after fertilization (D-7). The remaining four 

 batches were reared to 29 d after fertilization (D- 

 29). During the process we attempted to dupli- 

 cate natural water quality conditions as much as 

 possible. Temperatures were maintained at 

 18°C, and oxygen content was at or near satura- 

 tion throughout the experiments. Photoperiod 

 and light qualities were kept close to natural. Sa- 

 linities were zero from fertilization to D-4, 1.0 %<• 

 from D-5 to D-13, and 3%« from D-14 to D-29. 

 Each day containers were cleaned and new 

 water and food were added. An endemic small (1- 

 2 /jm) green phytoplankter (Nephroselmus sp.) 

 was also added in concentrations of 10 2 -10 3 /ml. 



Larvae began feeding consistently on D-7, at 

 which time they were given newly hatched, live 

 Artemia salina nauplii (San Francisco Bay 

 Brand). The range of initial food concentrations 

 was selected to include the estimated natural 

 zooplankton densities (0.003 to 0.010/ml (Daniel 

 1976)) and the concentrations used in other 

 striped bass research. Initial concentrations 

 were 0.00, 0.01, 0.10, 0.50, 1 .00, and 5.00 Artemia/ 

 ml. 



To estimate daily exogenous food rations of lar- 

 vae we used the following formula: daily food 

 ration = (average stomach contents)( hours of 

 active feeding)/digestive time. Detailed studies 



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