determine how environmental factors affect survival of a larval cohort. 

 Environmental factors act in concert, and it is the sum of experiences over the 

 entire embryo and larval stages that determines whether a good or poor year 

 class results. A bio assay for 96 hours, testing one or two factors, usually can 

 provide only a rough evaluation of the potential effect of the factor(s) on 

 recruitment. More meaningful conclusions can be drawn from investigations 

 that encompass the entire larval period. Many studies of that kind have been 

 carried out on larvae of freshwater fishes (69), but the difficulties in rearing 

 larvae of marine species have limited most bioassay research to embryo and 

 yolk-sac larva stages. 



Experiments in large volumes of seawater, either in plastic bag enclosures, 

 such as those used in recent Controlled Ecosystems Pollution Experiments 

 (CEPEX) (70) or in large tanks (74) hold great promise because whole 

 communities can be entrapped in such volumes. Effects of predation and 

 competition can be evaluated. Direct and indirect effects of added pollutants 

 on each trophic level can be observed. Recruitment success or failure by fishes 

 in such systems can be interpreted in the context of observed changes that 

 took place in the plankton community during the course of larval 

 development. 



Other approaches include transitional studies that combine laboratory and 

 field experiments. The "field bioassay" developed by Lasker (56) uses 

 laboratory-reared larvae in shipboard experiments, in which larvae are reared in 

 natural seawater sources to evaluate the potential of particular water masses to 

 support larval survival and growth. The recent discovery, based on laboratory 

 studies, that daily growth rings are present on otoliths of larvae, will allow 

 better estimates of larval growth and mortality rates in the sea (26, 93), and 

 also wOl allow comparison of growth in the laboratory with growth under 

 natural conditions. 



Except for swimming-feeding behavior of a few species and behavioral 

 responses to varying light levels (12, 15, 17) little is known about normal 

 behavior patterns of larvae or changes in behavior induced by environmental 

 effects. Behavioral studies not only can increase our understanding of how 

 pollutants affect larval behavior, but they also can provide important insight 

 into how predation and competition operate during the larval stage. 



There are many techniques presently available that allow environmental 

 factors and their effects on marine fish larvae to be evaluated. In the next 10 

 years, culture of marine fishes will be routine procedure at many laboratories; 

 and as more data accumulate, some of the seemingly contradictory results 

 obtained to date, especially with regard to critical food concentrations, will be 

 resolved. Additional species of marine fishes need to be tested for larval 



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