FISHERY BULLETIN: VOL. 73, NO. 1 



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1973 BONGO NET COLLECTION 



1972 CHANNEL NET DIP NET 



COLLECTION 



1973 CHANNEL NET DIP NET 



COLLECTION 



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 TIME OF DAY 



Figure 2. — Variation in diel cycle of gastrointestinal contents 

 in postlarval Atlantic menhaden. 



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1973 BONGO NET COLLECTION 



1972 HAUL SEINE DIP NET 



COLLECTION 



1973 HAUL SEINE DIP NET 



COLLECTION 



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 TIMt OF DAY 



Figure 3. — Variation in diel cycle of gastrointestinal contents 

 in postlarval pinfish. 



(18-24 mm, x = 21.5 mm) collected by dip net at 

 one location and between 0830 and 1030 h over 

 a 4-day period had little variation in their mean 

 gut contents. Spot larvae collected 2 April 

 averaged 25.3 copepods/fish (SE = 2.3), on 3 April, 

 21.3 (SE = 2.0), and on 5 April, 26.3 (SE = 3.7). 

 The similarity of food quantity in the larval 

 digestive tracts suggests that prey abundance 

 may have remained relatively constant over the 

 4-day period thus allowing the fish to consume 

 similar amounts of food. 



ESTIMATES OF 

 LARVAL GUT CAPACITIES 



Laboratory feeding experiments were con- 

 ducted at 15°-16°C to estimate the maximum gut 

 capacity of the larvae. The fish were fed high 

 densities of Arte mia nauplii until their digestive 

 tracts were completely packed from esophagus to 

 anus. Menhaden (28-32 mm, x = 30 mm TL) fed 

 for 20 min on a concentration ofArtemia nauplii, 

 3 nauplii/cm^, had an average of 145 nauplii/fish 

 in their digestive tracts (SE = 9.6). Spot larvae 

 (19-23 mm, x = 21 mm TL) fed for 15 min on 0.3 

 nauplius/cm^ had an average of 89 (SE = 7.0) 

 nauplii/fish; and pinfish ( 16-20 mm,x = 18 mm TL) 

 fed for 1 h on 0.3 nauplius/cm^, had an average 

 of 75 (SE = 15.1) nauplii/fish. By comparing 

 individual Artemia and copepods of the four 

 major taxa side by side under a microscope, we 

 estimated that the volume of two 450-/um 

 Artemia nauplii were equivalent to that of one 

 650- jum copepod. Using 0.5 as a conversion factor, 

 we calculated maximum gut capacities in terms 

 of copepods. Menhaden larvae of 30 mm have a 

 gut capacity of 72 copepods, 21-mm spot a gut 

 capacity of 44 copepods, and 18-mm pinfish a gut 

 capacity of 37 copepods. These estimates of gut 

 capacity were comparable to the maximum 

 numbers of copepods observed in the digestive 

 tracts of larval fish collected in the estuary for 

 spot (36.5 copepods/fish) (Figure 1) and pinfish 

 (35.3 copepods/fish) (Figure 3), but not for men- 

 haden (5.2 copepods/fish) (Figure 2). This large 

 difference between gut capacity and observed gut 

 contents suggests that menhaden larvae either 

 feed very little under natural conditions, and 

 never approach the estimated maximum gut 

 capacity or capture and/or handling causes them 

 to regurgitate or defecate causing inaccuracy 

 in our estimate of natural gut content. To test 



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