FOOD AND FEEDING OF LARVAE OF THREE FISHES OCCURRING 



IN THE CALIFORNIA CURRENT, SARDINOPS SAGAX, 



ENGRAULIS MORDAX, AND TRACHURUS SYMMETRICUS^ 



David K. Arthur- 



ABSTRACT 



The size, number, and types of food particles eaten by larvae of Pacific sardine, Sardinops sagax; 

 northern anchovy, Engraulis mordax; and jack mackerel, Trachurus symmetricus, were determined 

 by an examination of gut contents of larvae captured in plankton samples from the California Current. 

 Food particles found in larvae of the three fishes were predominantly the eggs, nauplii, and the 

 copepodid stages of the smaller species of copepods. These increased in width as the larvae grew though 

 not so uniformly for the anchovy as for sardine and jack mackerel. Particles ingested by anchovies at 

 first feeding were slightly larger than were those ingested by sardines, while jack mackerel could eat 

 particles three times wider than sardines of equal length. The smallest individuals of each species were 

 the most euryphagous, especially anchovies. Feeding incidence of sardine and anchovy declined during 

 the early larval period while that of jack mackerel increased. Sardine and anchovy larvae fed only 

 during the day. The data were not analyzed for day-night feeding for jack mackerel. 



The relative body depth and relative weight of laboratory-grown anchovy larvae increased 

 throughout the larval periods examined, whereas, the relative body depth of most ocean-caught 

 anchovy larvae decreased during the first half of this period, possibly as a result of the poorer ration 

 obtainable in the ocean. The decline in relative body depth of ocean-caught anchovy larvae may be 

 related to the decline in feeding incidence and to the apparent lack of increase in size of the food 

 particles ingested. 



Owing to the impending collapse of the Pacific 

 sardine, Sardinops sagax, fishery, a biological- 

 oceanographic survey program, which later 

 became known as the California Cooperative 

 Oceanic Fisheries Investigation (CalCOFI), was 

 initiated in March 1949. Instrumental in initiating 

 a program to study the food of the sardine larva 

 was the concept developed by Hjort (1914) that the 

 success of a year's spawning may be determined at 

 the critical period when the fragile larvae must 

 secure sufficient food from their environment. For 

 a recent and thorough review of the literature 

 concerning this subject, the reader is directed to 

 May (1974). 



To explore the possibilities proposed by Hjort 

 (1914), 10,408 sardine larvae from 398 samples 

 were examined. Food of two potential competi- 

 tors, namely the northern anchovy {Engraulis 

 mordax, 2,350 specimens, 69 samples) and the jack 

 mackerel {Trachurus symmetricus, 750 



'Based on a portion of a dissertation submitted in partial 

 satisfaction of the requirements for the Ph.D. degree at the 

 University of California, Scripps Institution of Oceanography. 



^Visiting Scientist, Southwest Fisheries Center, National 

 Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 

 92038. 



specimens, 65 samples) was also investigated 

 (Arthur 1956). Larvae of these three fishes were 

 supplied to me by Elbert H. Ahlstrom and came 

 from samples taken during early years of the 

 CalCOFI program. 



Sardines no longer support a viable fishery, but 

 anchovies have increased in numbers to fill, in 

 part, the ecologic if not economic void. Increasing 

 attention, therefore, will be paid in this paper to 

 this fish and to other species of the genus En- 

 graulis which occupy coastal environments of 

 many parts of the world (Reid 1967). 



METHODS 



Specimens were examined in glycerin because 

 of its advantages over water. Its clearing qualities 

 aid in the detection of food particles within the 

 gut, and the greater viscosity of this medium 

 dampens the movement of particles during dis- 

 section. Also, when in glycerin, larvae seem to be 

 more pliable and the intestinal walls do not tend to 

 fragment so readily. 



At first the entire intestinal tract of each sar- 

 dine larva was dissected from the body. This 



Manuscript accepted Februarv' 1976. 

 FISHERY BULLETIN: VOL! 74, NO. 3, 1976. 



517 



