ARTHUR: FOOD AND FEEDING OF LARVAL FISHES 



250 



E 200 

 § '50 



O 100 



UJ 

 N 



c/5 50 



4 5 6 7 8 9 10 II 

 LENGTH OF LARVAE (mm) 



12 



Figure l.-Food size of Pacific sardine larvae. The line is a least 

 squares fit to all data points and is expressed by the equation: S 

 = 13.04L + 5.70, where S is width of food in microns and L is 

 standard length of larvae in millimeters. The correlation 

 coefficient r is 0.813 and the coefficient of determination r- 

 implies that 66% of the variation in food size can be explained by 

 lan'al size alone. 



a particular sample and is considered a measure of 

 a larva's ability to obtain food in the environmen- 

 tal circumstances at the time of sampling. 



The available data permit an inspection of the 

 average hour-by-hour series of trophic events for 

 sardine larvae (Figure 2). The data were divided 

 into 16 intervals composed of: the first half hour, 

 the second half hour, the second hour, and the third 

 hour both before and after sunrise, and both 

 before and after sunset. There were also midday 

 and midnight intervals which vary in length 

 according to the season. Only those intervals in 

 which at least 50 larvae from at least five samples 

 were included. Feeding incidence of all three size 

 groups increased throughout the day. This could 

 have resulted from accumulation of food in the 

 gut, or perhaps to the success of larvae in finding 

 more suitable feeding conditions as the day pro- 

 gressed. The largest size group demonstrated the 

 fastest return to a low feeding incidence at night 

 which probably reflects faster digestive rates for 

 older larvae, as has been shown for plaice larvae 

 (Yasunaga 1971). The lower feeding incidence of 

 older larvae may, therefore, be partly due to an 

 increased digestive rate. 



Figure 2 illustrates the diurnal nature of feed- 

 ing which is due to the visual feeding sardine larva 

 requiring light to detect its prey. (Schumann 

 1965). This results in diurnal changes of the 

 intestine. The posterior intestine of larvae cap- 

 tured during the early morning is visibly striated. 



c 



O) 



o 



0) 



a. 



UJ 



o 



UJ 

 Q 

 O 



z 



Q 

 UJ 

 UJ 



Sunrise 

 30 



20 - 



->Day 



-^ Sunset 



-^ Night 



• - End of yolk-soc to 

 5 Smnn 



O-6 to 9 5mm 



A-- 10 0mm 



> Sunrise 

 130 



-20 



Average of 



remenfs 



123 321 123 321 



HOURS BEFORE AND AFTER SUNRISE OR SUNSET 



Figure 2.-Diurnality of feeding incidence of Pacific sardine 

 larvae. Only those intervals in which at least 50 larvae coming 

 from at least 5 samples are included. 



In late afternoon and early evening, the posterior 

 intestines of many larvae, especially the smaller 

 ones, are expanded and have no visible striations. 

 The intestinal wall contains large vacuoles of clear 

 fluids. During this period of the day, it is common 

 to capture larvae with greatly expanded intestines 

 but with no identifiable food organisms. Often 

 such larvae contain some granular material float- 

 ing about in the intestinal lumen which is com- 

 paratively large due to the expansion of the 

 surrounding wall. During the night, intestinal 

 expansions disappear and by sunrise almost all of 

 the larvae have returned to the compact, striated 

 intestinal condition. This rhythm is most pro- 

 nounced in the smallest size group where, as 

 indicated in Figure 2, the amplitude of the diurnal 

 feeding incidence is at a maximum. 



FOOD OF ANCHOVY LARVAE 



Type of Food 



No larva was found containing both yolk and 

 ingested food. The diet of anchovy larvae (Table 

 2) is very similar to that of the sardine. The most 

 striking difference is that very young anchovies 

 are more euryphagous. About 40% of their diet (by 

 numbers) consists of noncrustacean food particles. 

 A food category entitled "unidentified spheres" is 

 represented by small (about 20 fim) objects, 

 probably of plant origin. Copepod nauplii become 

 increasingly important as anchovy larvae increase 

 in length and compose the bulk of particulate food 

 when all sizes of larvae are considered. 



Copepod eggs and nauplii were found to be the 

 most important element in the diet of larvae of 



519 



