A BIOENERGETIC MODEL FOR THE ANALYSIS OF 



FEEDING AND SURVIVAL POTENTIAL OF WINTER FLOUNDER, 



PSEUDOPLEURONECTES AMERICANUS, LARVAE DURING 



THE PERIOD FROM HATCHING TO METAMORPHOSIS 



Geoffrey C. Laurence 1 



ABSTRACT 



A bioenergetic model was developed which simulated effects of temperature, prey density, and larval 

 size on ability of winter flounder, Pseudopleuronectes americanus, larvae to obtain food energy to 

 provide for experimentally determined growth and metabolism. Larval feeding at constant tempera- 

 ture and as a function of prey concentration was exponential and more sharply asymptotic in younger 

 fish than in those near metamorphosis. Specific growth rates were exponentially related to prey 

 concentrations and ranged from 5.72 to 8. 70% /day at survival prey concentrations of 3.7 to 21.7 cal/ 

 liter. Daily required feeding time was directly related to prey availability. Critical plankton densities 

 below which larvae did not have enough time during the day to obtain adequate food for growth 

 and metabolism varied with age and ranged from 2.1 to 5.7 cal/liter. Simulated physiological energy 

 utilization and required caloric food intake were inversely related to prey concentration and varied 

 with larval stage of development. Food requirements expressed as numbers of copepod nauplii 

 consumed per day ranged from 19 for first feeding larvae to 235 for metamorphosed juveniles. 

 Predicted gross growth efficiencies were directly related to prey concentration and increased with 

 age from 5 to 33%. All indications pointed to a "critical period" of larval survival during the period 

 of exogenous feeding initiation and immediately after. 



One of the important problems in fishery research 

 and management is identifying and understand- 

 ing the functional mechanisms of the stock- 

 recruitment relationship. It is becoming more 

 apparent that focusing attention on studies of 

 mortality in the early life stages, particularly 

 the larval stage, may help in this understanding. 

 Mortality rates are usually the highest and most 

 variable from year to year during the early life 

 stages. Because of this, even small changes in 

 mortality during this period can produce a mag- 

 nified effect on the eventual numbers of recruits 

 to sport or commercial fisheries. 



Other than predation, the most important prob- 

 able factors influencing larval mortality are food 

 and feeding relationships and the influence of en- 

 vironmental parameters on these processes. The 

 acquisition of the required food ration by fish 

 larvae is of prime importance in survival and 

 successful development. Without the proper quan- 

 tity and quality of food, larvae will be adversely 



'Northeast Fisheries Center Narragansett Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, Narragansett, RI 

 02882. 



Manuscript accepted December 1976. 

 FISHERY BULLETIN: VOL. 75. NO. 3, 1977. 



affected and survival will be influenced. Bio- 

 energetic relationships have been studied exten- 

 sively for adult fishes, and the works of Ivlev 

 (1939a, b, c), Winburg (1956), Paloheimo and 

 Dickie (1966a, b), and Warren and Davis (1967) 

 are among the most complete. However, the use 

 of energy resources in physiological mechanisms 

 and the relationships of feeding, growth, and sur- 

 vival in the early life stages of fishes have only 

 recently been studied (Ivlev 1961a, b; Lasker 

 1962; Laurence 1969, 1973). 



It is the object of this research to examine the 

 effects of food and feeding on winter flounder, 

 Pseudopleuronectes americanus, survival from 

 the period of hatching to metamorphosis and to 

 develop a model of these critical processes. The 

 model includes the forcing variables of tempera- 

 ture, prey density, and larval size or age and their 

 effects on the ability of winter flounder larvae to 

 successfully acquire energy rations necessary for 

 experimentally determined growth and metabolic 

 parameters. The energy rations are quantified as 

 to caloric value of ration, numbers of specific prey 

 organisms consumed, time for required intake, 

 and metabolic parameters dealing with conver- 

 sion into fish flesh. 



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