FISHERY BULLETIN: VOL. 75, NO. 3 



relationship between oceanographic conditions 

 and larval anchovy food organisms. In 1975 he 

 found that G. splendens was replaced as the dom- 

 inant organism in the chlorophyll maximum layer 

 by the armored dinoflagellate, Gonyaulax poly- 

 edra, and later by a variety of small diatoms. In 

 an effort to assess effects that this succession 

 might have on survival of anchovy larvae, we 

 have conducted feeding experiments with some of 

 the phytoplankters common in the Southern Cal- 

 ifornia Bight to determine which species are ac- 

 ceptable as food by anchovy larvae. In addition, 

 we have examined the relative nutritional value 

 of Gymnodinium splendens and Gonyaulax 

 polyedra. 



METHODS AND MATERIALS 



Phytoplankton Cultures 



The phytoplankters chosen for feeding experi- 

 ments are common to southern California coastal 

 waters, and most were major components of the 

 chlorophyll maximum layers during 1974 and 

 1975 (Lasker in press). Also, they were of an appro- 

 priate size for ingestion by first feeding anchovy 

 larvae (Table 1). Axenic cultures of the selected 

 phytoplankters were supplied by James Jordan 

 of the Food Chain Research Group at Scripps 

 Institution of Oceanography. Culture techniques 

 were described by Thomas et al. (1973). 



TABLE 1. — Average dimensions of phytoplankters offered as 

 food to first feeding anchovy larvae. 



BACILLARIOPHYCEAE: 



Ditylum bnghtwellii (25  150/xm, single cells) 

 Chaetoceros affinis (4/xm wide in chains to 200^m) 

 Thalassiosira decipiens (8 x '\0fim, single cells) 

 Leptocylindrus danicus (5jim wide in chains to 75^m) 

 DINOPHYCEAE: CHLOROPHYCEAE: 



Gymnodinium splendens (51 /xm) Chlamydomonas sp. (10/xm) 



Gonyaulax polyedra (40/xm) Dunaliella sp. (6/xm) 



Prorocentrum micans (27 x 38/xm) 

 Pendinium Irochoideum (20/xm) 



Feeding Experiments 



To determine which phytoplankters are preyed 

 upon by anchovy larvae, feeding experiments 

 were conducted using methods similar to those of 

 Lasker (1975). Cylindrical 8-liter battery jars, 

 wrapped with dull black cardboard, were filled 

 with approximately 5 liters of filtered seawater 

 (filter pore size, 5 ttm) and inoculated from a 

 dense culture of the phytoplankton to be tested. 



The densities were determined by counting or- 

 ganisms in 1-ml alilquots in a Sedgwick- Rafter 3 

 counting chamber and/or with a Coulter Counter 

 Model Ta, and the size was measured with an 

 ocular micrometer. Experiments were conducted 

 at temperatures ranging from 16.9° to 19.6°C, and 

 the test jars were illuminated from above with a 

 bank of four 40-W fluorescent lamps. Light inten- 

 sity at the surface of the test jars was approxi- 

 mately 2,400 lx. Because anchovy larvae readily 

 feed on Gymnodinium splendens (Lasker 1975), 

 at least one container in each series of experi- 

 ments contained only this food organism as a con- 

 trol to test the feeding ability of each batch of 

 larvae. 



Diatoms were maintained in suspemsion dur- 

 ing the feeding trials by a gentle stream of bubbled 

 air in each test jar. To evaluate the effect of such 

 agitation on the ability of larvae to feed, experi- 

 ments were conducted with and without bubbled 

 air using G. splendens as food. Little effect on 

 feeding ability could be detected (Table 2, Trial 1). 



Anchovy eggs were obtained from adult ancho- 

 vies maintained in spawning condition at the 

 Southwest Fisheries Center Laboratory. Spawn- 

 ing techniques were described by Leong (1971). 

 Anchovy eggs and larvae were allowed to develop 

 in 1-liter jars (100 eggs/jar) containing filtered 

 seawater (filter pore size, 5 /xm). First feeding 

 larvae (2.5 days after hatching at 17°C) were 

 placed in the experimental containers with the 

 test organism for approximately 8 h before being 

 siphoned from the containers and quickly im- 

 mobilized on a membrane filter (pore size, 8 /urn) 

 by vacuum filtration. This technique helped to 

 prevent the larvae from defecating (Lasker 1975). 

 The larvae remained somewhat transparent after 

 air drying so that the presence of food in the gut 

 could be determined by microscopic examination 

 of the intact animal. 



Larval Rearing Experiments 



Anchovy larvae were reared for 10 days in 10- 

 liter circular containers immersed in a tempera- 

 ture-controlled bath in an air-conditioned room 

 (Lasker et al. 1970). The containers were filled 

 with membrane filtered seawater (pore size, 

 0.45 /xm), the salinity was33.4°/oo,and the temper- 

 ature was maintained at 16.0° ± 1.1°C. Lighting 



3 Mention of trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



578 



