(channel net versus dip net) between areas were 

 not felt to bias the results. We observed no differ- 

 ences in the length of fish sampled (by species) or 

 in the density of copepods at the two locations. 



These results indicate that larval feeding rates 

 are limited when the fish are exposed to current. 

 Current speed ranged from to 5.5 m/s in mid- 

 channel where feeding was low, to no measur- 

 able current along the shore where more feeding 

 occurred (Table 1). In addition, pinfish collected 

 in the channel on a slack tide contained 4.1 cope- 

 pods/fish compared with a mean of 1.3 copepods/ 

 fish when there was a current present. 



Laboratory experiments indicated that current 

 speed affected the food consumption rate of both 

 species (Table 2). Pinfish consumed the most food 

 when there was no current, but spot ate more at a 

 current velocity of 1.7 m/s. Pinfish ate the least 

 food in a 5.1 m/s current while the spot minimum 

 feeding occurred at varied current speeds. Both 

 species fed at a higher rate when fish densities 

 were lower. 



The observations from both field and laboratory 

 studies indicate that postlarval pinfish feeding de- 

 clines as current speed increases. These results 

 suggest that current speed influences the ability of 

 pinfish to capture their prey, although the specific 

 reasons for such altered behavior are unknown. 

 The well-known attack behavior of larval fish, 

 that of visually sighting the prey and of assuming 

 an S-shape prior to striking (Blaxter and Holliday 

 1963), may be unattainable by postlarval pinfish 

 exposed to higher current speeds. Bishai (1959) 

 found that larval herring drift with a current at 

 speeds less than the current itself. This may 

 suggest that the size, shape, and behavior of a 

 plankter may influence its rate of movement in a 

 current. Prey organisms may move at a faster rate 

 than the fish larvae, which in turn may lessen the 

 ability of the fish to orient to the prey. 



Current also may destroy the microstructure of 

 the prey population. Without a strong current, 

 food could aggregate in patches thus producing 

 local areas with high food density and therefore 



FISHERY BULLETIN: VOL. 74, NO. 2 



increase the rate of ingestion. This latter explana- 

 tion is probable in the natural environment; how- 

 ever, it appears unlikely under the laboratory 

 conditions, because the density of Artemia in the 

 tanks was very high (1/ml) and prey were re- 

 plenished to assure that it did not decrease. In 

 addition, the small cross-sectional area (100 cm^) 

 and volume of the tanks greatly limited the dis- 

 tance a larva had to travel to find food even if prey 

 were in a patch configuration. 



Differences in channel versus shoreline feeding 

 by spot in the natural environment (Table 1) are 

 similar to those of pinfish; however, feeding by 

 spot in the laboratory was highly variable and is 

 difficult to explain. Spot fed at the highest rates 

 when a slight current was present and even fed at 

 a high rate when exposed to a maximum current of 

 5.1 m/s. The spot postlarvae used in the studies 

 were larger than the pinfish and this may explain 

 the ability of spot to feed at a high rate when 

 exposed to current, because increased size usually 

 improves swimming ability which may improve 

 the fish's ability to capture their prey. However, 

 species differences in swimming ability were not 

 apparent: larvae of both species moved freely 

 about the tank when current was absent; oriented 

 into the current or at times drifted with the cur- 

 rent at the 1.7 m/s speed; and drifted along with 

 the current in the 5.1 m/s current, although some 

 individuals oriented into the current briefly. Simi- 

 lar behavior by larval fishes exposed to varied 

 current velocities was discussed by Bishai (1959) 

 and Houde (1969). Ryland (1963) indicated that 

 the mechanisms by which larval fishes orient to a 

 current are poorly understood. The lower feeding 

 rate of spot in no current is unexplainable unless 

 this species is adapted in some way to be more 

 effective at capturing prey within a current. 

 Serebrov (1973) also found differences in the feed- 

 ing intensity of various species (guppy, Poecilia 

 reticulata, and European dace, Phoxinus phoxi- 

 nus) when exposed to different current velocities 

 and suggested that the differences were due both 

 to natural adaptation to certain current condi- 



TaBLE 2. — Digestive tract contents (mean number oiArtemia nauplii/larva ± 1 SE) of 

 larval fishes following feeding in the laboratory under several current velocities. 



'Fifty fish. 



^One hundred fish. 



426 



