ARTHUR: FOOD AND FEEDING OF LARVAL FISHES 



40 



35 



• - Engraulis mordax, Arthur 



o - Engraulis mordax, Berner 



A - Engraulis anchoita, CiechomskI 



A - Engraulis japonica, Nokai et al 



1956 

 1959 

 1967 

 1969 



14 18 22 26 30 34 



LENGTH OF LARVAE (mm) 



46 



Figure 8.-Feeding incidence of larvae of various species of 

 anchovy. Values are the average of day and night feeding (day 

 values are divided by two because young anchovy larvae do not 

 feed at night). Berner's data were recalculated to read "feeding 

 incidence per length of larva" rather than "percent of feeding 

 larvae occurring per length." 



living in their natural environment? This could be 

 partly a result of a faster digestive rate of older 

 larvae as indicated for sardine larvae (Figure 2). It 

 also could result if either the ambient food density 

 decreases with time or the larval feeding activity 

 decreases with age. There are reasons to suspect 

 that both of these might occur and at the same 

 time. 



Decrease in Food Density 



Sardine and anchovy larvae may initiate their 

 first feeding in higher concentrations of food than 

 they will experience several days later. Hand and 

 Berner (1959) found that 74% of the food of adult 

 sardines, when filter feeding at night, were small 

 species of copepods, presumably the same species 

 that produce the small nauplii so important in the 

 diet of the sardine and anchovy larvae. Further- 

 more, they found that organisms in stomach 

 contents had a high correlation with organisms in 

 plankton samples taken at the same time and 

 place. The adult anchovy, when feeding at night, is 

 probably also a filter-feeding zooplanktivore al- 

 though it does have more omnivorous tendencies 

 (Loukashkin 1970), and the type of feeding, either 

 biting or filtering, is controlled by the size of the 

 food particles available (Leong and O'Connell 

 1969; O'Connell 1972). Both species also are selec- 

 tive feeders on larger organisms when visual 

 conditions permit. As a consequence, filter-feed- 



ing adults by actively searching for rich feeding 

 conditions for themselves also prospect areas 

 suitable for their larvae. More sardine and an- 

 chovy larvae were shown to occur in samples where 

 both species were collected than in hauls where 

 they occurred alone (Ahlstrom 1967); he concluded 

 that these samples were collected near centers of 

 heavier spawning for both species. It would appear 

 that spawning adults of the two species were 

 seeking out the same conditions. Sardines (Ahl- 

 strom 1954), northern anchovies (Bolin 1936), and 

 Argentine and other anchovies (Ciechomski 1965) 

 spawn at night. Both spawning and filter feeding 

 take place at night; therefore, the eggs may be laid 

 near concentrations of suitably sized copepods 

 (assuming spawning and feeding occur on the 

 same night). However, as soon as the eggs have 

 been spawned, they begin to be dispersed by water 

 movement from each other and from organisms 

 they will need for food several days hence. Sardine 

 eggs are spawned in dense patches according to 

 Smith (1973), who calculated that the horizontal 

 mean distance between nearest neighbor eggs is 

 of the order of 1 to 2 cm at spawning and changes 

 to 15- to 20-cm mean distance for several-day-old 

 larvae. These larvae may experience a diminution 

 of their early feeding conditions as a result of 

 diffusion as well as of grazing by the various 

 predators. These ideas are presented to suggest 

 how a general dilution of the co-occurrence of o^^g 

 and plankton patches could occur in time. Lasker 

 (1975) has recorded how rich larval feeding condi- 

 tions can be destroyed overnight by a single storm. 



Condition of Ocean-Caught and Laboratory- 

 Grown Anchovy Larvae 



There are differences in physical condition of the 

 average ocean-caught and laboratory-grown an- 

 chovy larvae. These differences are probably a 

 result of the available food. 



Ahlstrom et al.^ have presented a series of 

 measurements of anchovy larvae and juveniles 

 taken randomly from samples of the CalCOFI 

 program. Figure 9 is a scatter diagram of relative 

 body depths (body depth measured just anterior to 

 pectoral fin base ^standard length) calculated 

 from the above date. This diagram demonstrates 

 that relative body depths of ocean-caught anchovy 



^Ahlstrom, E. H., D. Kramer and R. C. Counts. Egg and larval 

 development of the northern anchovy, Engraulis mordax. 

 Unpubl. manusc. 



525 



