(e.g., T. mexicaniis, Cyclothone acclinidens, C. sig- 

 nata, Sternoptyx diaphana) is usually quite low. 

 Obviously a dead fish cannot swallow cod end 

 material while a stressed but living fish may. The 

 survival factor may have caused some of the dif- 

 ferences between our results and those of Hopkins 

 and Baird ( 1975); off California the survival rate 

 of trawled specimens is relatively high (Childress 

 et al. 1978) while in the Gulf of Mexico it is very 

 low (T. L. Hopkins and R. C. Baird, pers. com- 

 mun.). Survival rate is probably influenced by 

 haul duration, the depth and temperature range 

 sampled, cod end design, and net construction. 



It is also apparent that specimen size can 

 influence the degree of net feeding. It is not clear 

 whether this is due to the greater survival rate of 

 larger individuals or to their larger mouth size. 

 Within the limits of survival rate and size vari- 

 ables, the degree of exposure to prey in the cod end 

 is a function of haul duration, the depth strata 

 sampled, and the amount of time a fish spends in 

 the cod end. Discrete-depth hauls probably de- 

 crease the degree of exposure by limiting the 

 number and diversity of prey items while oblique 

 hauls increase exposure. The data also indicate 

 that small prey aire more readily ingested in cod 

 ends than large prey. Accordingly, the bias im- 

 parted to stomach content analyses by net feeding 

 would be toward the smaller prey items. 



Postcapture ingestion is a complex problem and 

 no clear-cut conclusions can be drawn from the 

 available data except that it occurs to a varying 

 degree and that the extent of its occurrence is 

 subject to fish survival, fish size, and exposure. To 

 gain a predictive capability it will be necessary to 

 investigate these factors further. 



Acknowledgments 



We thank J. L. Cox, J. J. Childress, L. B. Quetin, 

 J. J. Torres, and D. K. Vaughan for tlieir help at 

 sea and in the laboratory. We are grateful to T. L. 

 Hopkins and R. C. Baird for their reviews of the 

 manuscript. The research was supported in part 

 by NSF grants OCE76-02251. OCE78-09018, and 

 OCE76-10407-1. Preliminary and experimental 

 studies were conducted aboard the research ves- 

 sels A/p/jo Helix. VeleroIV, andEllen B. Scripps. 



Literature Cited 



Baker. A. Dec. m. r. Clarke, and M, J. H.arris 



1973. The N.I.O. combination net (RMT 1 + 8) and further 



developments of rectangular midwater trawls. J, Mar, 

 Biol, Assoc. U.K, 53:167-184, 



Childress, J, J,, A, T, Barnes, L. B. Quentin. and B, H, 



ROBISON, 

 1978, Thermally protecting cod ends for the recovery of 

 living deep-sea animals, Deep-Sea Res. 25:419-422, 



Hopkins, T, L,, and R, C, Baird, 



1975, Net feeding in mesopelagic fishes. Fish Bull,, U,S, 



73:908-914, 

 1977, Aspects of the feeding ecology of oceanic midwater 



fishes. In N, R. Anderson and B, J, Zahuranec (editors). 



Oceanic sound scattering prediction, p, 325-360, Plenum 



Press. N.Y, 



Thomas M, Lancraft 

 Bruce H. Robison 



Marine Science Institute 

 Uniuersity ofCalifornia 

 Santa Barbara. CA 93106 



INHIBITORY EFFECT OF THE ALGA 



PAVLOVA LVTHERIl ON GROWTH OF 



MUSSEL, MYTILVS EDVLIS. LARVAE 



The culture of bivalve larvae sometimes appears 

 to be more of an art than a science. Many factors 

 can influence the growth and survival of larvae 

 and it is usually difficult to assign a cause to the 

 failure of a particular culture. In one instance we 

 had set up a large experiment with mussel, 

 Mytilus edulis. lai-vae and noticed after 5-8 days 

 that the larvae had ceased to grow in all of our 

 treatments but that they remained alive and ac- 

 tive. During this experiment one factor was 

 known to have been changed: Previously we had 

 been feeding the larvae a mixture of the algae 

 Isochrysis galbana and Pavlova lutherii. while in 

 this experiment only P. lutherii was available. 



There has been one account in the literature 

 (Fretter and Montgomery 1968) of P. lutherii 

 being toxic; yet Bayne (1965) found P. lutherii to 

 support normal growth in A/, edulis larvae. Davis 

 and Guillard ( 1958) found P. lutherii to be as good 

 as I. galbana (and about as good as a mixture of 

 the two) when fed to larvae of Crassostrea vir- 

 giiiiea and Mercenaria mercenaria . The results of 

 Wilson (1978) show thatP, lutherii is as satisfac- 

 tory as other algae as food forOstrea edulis larvae. 

 In order to determine whether our P. lutherii cul- 

 tures were to blame for the lack of growth we 

 observed, we set up an experiment to compare the 

 growth of mussel larvae when fed several diets of 

 algae. 



fishery bulletin, vol, 77. NO. 3, 1980. 



715 



