THE GENERAL FEEDING ECOLOGY OF POSTLARVAL FISHES 

 IN THE NEWPORT RIVER ESTUARY^ 



Martin A. Kjelson, David S. Peters, Gordon W. Thayer, and George N. Johnson^ 



ABSTRACT 



Food preferences, feeding intensity and chronology, evacuation rates, and daily rations were 

 determined for postlarval stages of Atlantic menhaden, Brevoortia tyrannus (25-32 mm); pinfish, 

 Lagodon rhomboides (16-20 mm); and spot, Leiostomus xanthurus (17-24 mm). Four copepod taxa, 

 Centropages. Temora, Acartia, and Harpacticoida, made up 76-99%' of the total gut contents. 

 Postlarval feeding intensity was greatest during early daylight hours. Postlarval menhaden lost 

 an estimated 60% of their orginal gut contents due to the stress of handling and capture. Similar 

 stress caused no food loss in either postlarval pinfish or spot. Gastrointestinal evacuation of 

 copepods and Artemia nauplii were described by linear regression. Evacuation rates varied 

 directly with the amount of food in the gut. Rate constants were used in conjunction with infor- 

 mation on the chronology of gut contents to determine daily rations. Daily ration estimates as a 

 percent of the fish's wet body weight were: menhaden, 4.9%; pinfish, 3.5%; spot, 4.3% and 9.0%. 

 The ration estimates for spot in terms of calories per fish per day were similar to the metabolic 

 needs estimated from oxygen consumption measurements but were lower than the estimates from 

 oxygen consumption for menhaden and pinfish. 



Larval and postlarval fish are significant con- 

 sumers in aquatic ecosystems, yet our knowledge 

 of their feeding habits and daily food consump- 

 tion is incomplete. This paper deals with the 

 general feeding ecology of the postlarval stages 

 of three common estuarine fishes. Four major 

 aspects are discussed. These include 1) food 

 preferences, 2) feeding intensity and chronology, 

 3) evacuation rate, and 4) daily ration. 



Postlarval Atlantic menhaden, Brevoortia 

 tyrannus; pinfish, Lagodon rhomboides; and spot, 

 Leiostomus xanthurus, were collected during 

 March of 1972 and 1973 from the Newport River 

 estuary, Carteret County, N.C. The fish (hereafter 

 referred to as larvae) were taken near Pivers 

 Island, approximately 2.5 km inside the Beaufort 

 Inlet. Pinfish and spot were collected using a 

 seine and dip nets, while menhaden were captured 

 in a channel net (Lewis et al. 1970) and with 

 dip nets. One additional group of samples was 

 collected in bongo nets. Most fish were frozen 

 immediately following capture, thus stopping 

 their digestive processes. The only exceptions to 

 preservations by freezing were the bongo net 



'This research was supported through a cooperative agree- 

 ment between the National Marine Fisheries Service and the 

 U.S. Atomic Energy Commission. 



''Atlantic Estuarine Fisheries Center, National Marine 

 Fisheries Service, NOAA, Beaufort, NC 28516. 



samples which were placed in 5% Formalin.^ 

 Food preferences were determined by examin- 

 ing the contents of entire digestive tracts. The 

 gut contents from 120 fish of each species col- 

 lected throughout the day were combined and 

 individual food items identified, counted, and 

 measured. Copepodite and adult copepods com- 

 posed 99-100% (by both number and volume) of 

 the identifiable food items in the digestive tracts. 

 The average-sized copepod fed upon by each larval 

 species was determined by measuring 100 cope- 

 pods chosen from the combined digestive tract 

 contents of all larvae collected in a 24-h period. 

 Diel periodicity of digestive tract contents indi- 

 cated the intensity and chronology of feeding by 

 the larvae. Twenty fish of each species were 

 collected at 4-h intervals for 24 consecutive hours. 

 Larval evacuation rates for copepods and for 

 Artemia salina were determined from laboratory 

 experiments performed at 15°-17°C and 25-30%o; 

 conditions which typify larval collection sites 

 during March. Copepod evacuation was deter- 

 mined by collecting larvae from the estuary, 

 placing them in food-free seawater tanks, and 

 observing the decrease in their gut contents 

 through time. At the time of initial capture 



Manuscript accepted March 1974. 



FISHERY BULLETIN: VOL. 73, NO. 1, 1975. 



^Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



137 



