SCURA and JERDE: PHYTOPLANKTON AS FOOD FOR LARVAL ANCHOVY 



2 3 



MICROZOOPLANKTON / ml 



2 3 



MICROZOOPLANKTON / ml 



FIGURE 1. — Percent survival of Engraulis mordax at 10 days in 

 relation to supplementation of a dinoflagellate diet with micro- 

 zooplankton. A) Gymnodinium splendens diet. B) Gonyaulax 

 polyedra diet. 



P<0.025) in larval survival. Larvae reared on a 

 G. polyedra diet required at least 1 microzoo- 

 plankton/ml in order to have survival rates that 

 were comparable to larvae reared on a diet of 

 Gymnodinium splendens. These results were 

 comparable to the survival rates recorded by 

 O'Connell and Raymond (1970) for anchovy larvae 

 fed copepod nauplii at various concentrations. 

 They found that larvae did not survive for 12 days 

 in containers with less than 1 nauplius/ml. 



Although anchovy larvae grow slowly during 

 the first several days of feeding, a slight but sig- 

 nificant increase (t = 2.67, P<0.05) in standard 

 length occurred in larvae fed G. splendens when 

 their diets were supplemented with microzoo- 

 plankton (Figure 2), but no differences in dry 

 weight were detected. Larvae fed Gonyaulax 

 polyedra also appeared to increase in standard 

 length when their diets were supplemented (Fig- 

 ure 2), but because the increase was slight and 

 the number of data points was small due to the 

 low survival rates on this diet, no significant in- 

 crease was detected (t = 1.50, P>0.20). 



Survival was low in larvae fed only 5 micro- 

 zooplankters/ml without any dinoflagellates (Ta- 

 ble 3). One container had no survivors and the 

 other had 19.9% survival. Theilacker and 

 McMaster (1971) found that larval anchovies that 

 were fed only rotifers (B. plicatilis) had a lower 



2 3 



MICROZOOPLANKTON / ml 



S.0 



55 



< 



a 



z 



, 0.09 X + 4.18 



2 3 



MICROZOOPLANKTON /ml 



FIGURE 2. — Standard lengths of Engraulis mordax at 10 days 

 in relation to supplementation of a dinoflagellate diet with 

 microzooplankton. A) Gymnodinium splendens diet. B) Gonyau- 

 lax polyedra diet. 



rate of survival than those fed Gymnodinium 

 splendens and B. plicatilis in combination. They 

 related this finding to the low feeding success of 

 larvae on the larger sized rotifers during the first 

 few days of feeding. Also, Houde (1973) believes 

 that survival of fish larvae is increased when 

 blooms of phytoplankton are maintained in rear- 

 ing containers to "condition" the water (presum- 

 ably by removing metabolites). 



DISCUSSION 



Anchovy larvae apear to select their prey and 

 it seems as if size is not the only criterion for 

 selection. Larvae did not feed on any of the four 

 species of diatoms tested in this study. The most 

 obvious explanation is that spines and other proc- 

 esses on the diatoms either discouraged the larvae 

 from striking or prevented them from swallowing. 

 On the other hand, most larvae fed on all species 

 of dinoflagellates tested. Visibility might also 

 play an important role in prey selection since the 

 darkly pigmented dinoflagellate, P. trochoideum, 



581 



