FURTHER OBSERVATIONS OF THE FEEDING ECOLOGY 



OF POSTLARVAL FINFISU, LAGODON RHOMBOIDES , 



AND SPOT, LEIOSTOMUS XANTHURUS^ 



Martin A. Kjelson and George N. Johnson^ 



ABSTRACT 



The effect of current on feeding, temporal variation in food consumption, and the effect of predator and 

 prey size on food preferences were evaluated for postlarval stages of pinfish, Lagodon rhomboides 

 (15-19 mm total length); and spot, Leiostomus xanthurus (16-22 mm). Field and laboratory observations 

 indicated that pinfish feeding rates decreased as water current velocity increased. Similar behavior 

 was noted in spot from field observations, but spot feeding rates in the laboratory were highest when a 

 slight current was present. Mean gut contents of postlarvae collected at midday over a 2-mo period 

 ranged from 0.4 to 38 copepods/fish. The mean coefficient of variation for the number of copepods per 

 fish in a single midday sample in = 20 fish ) was 20% . Maximum daily feeding rates were estimated at 17 

 and 26 copepods/h for spot and pinfish, respectively. Field and laboratory data confirmed that as 

 postlarvad size increases the size of their prey also increases. Refined estimates of postlarval evacuation 

 rates and daily rations also are presented. Daily ration estimates as a percent of the fish's wet body 

 weight were 99c for both species. The ration estimates for both species were greater than metabolic 

 needs estimated from oxygen consumption measurements. 



Information on the feeding ecology of larval fishes 

 is necessary to understand the role of larvae in 

 ecosystem energetics and community structure 

 and the importance of feeding conditions to year 

 class strength. However, relatively little is 

 known about the feeding of larval fishes. This 

 paper reports four major aspects of postlarval 

 feeding: 1) the effect of current speed on feeding 

 intensity; 2) temporal variation in postlarval food 

 consumption; 3) the relation of feeding rate to 

 food abundance; and 4) the effect of prey and 

 predator size on postlarval food preferences. 

 Refined results concerning postlarval evacuation 

 rates and daily rations also are presented. Our 

 earlier paper (Kjelson et al. 1975) stressed the 

 study of food preferences, feeding intensity and 

 periodicity, evacuation rates, daily rations, and 

 the effect of handling and capturing the fishes on 

 their digestive tract contents. 



Pinfish, Lagodon rhomboides , and spot, Leios- 

 tomus xanthurus, constitute a major portion of 

 the fish biomass of southeastern estuaries of the 

 Atlantic coast and thus are important to the 

 structure and function of these ecosystems. Spot 

 are also an important commercial food species. 



'This research was supported under agreement AT (49-7 )-5 

 between the National Marine Fisheries Service, NOAA, and the 

 U.S. Energy Research and Development Administration. 



^Atlantic Estuarine Fisheries Center, National Marine 

 Fisheries Service, NOAA, Beaufort, NC 28516. 



Both species are primarily winter spawners in 

 the Atlantic Ocean with larvae migrating inshore 

 to estuarine waters which serve as nursery 

 grounds between spring and fall. Larval forms 

 (here defined as individuals <11 mm) are rarely 

 found within the estuaries, whereas postlarval 

 stages (here defined as fish between 11 and 22 

 mm) occur both in nearshore oceanic and es- 

 tuarine waters. 



METHODS 



General 



Postlarval pinfish (15-19 mm total length (TD) 

 and spot (16-22 mm) were collected during 

 January and February 1974, from the Newport 

 River estuary, N.C., following their recent im- 

 migration into the estuary from the offshore 

 spawning grounds in the Atlantic Ocean. All fish 

 were collected at Pivers Island, 2.5 km inside the 

 Beaufort Inlet. Shore samples were collected with 

 dip nets while those in the adjacent channel were 

 collected with a channel net (Lewis et al. 1970). 

 Fish were anesthetized immediately upon cap- 

 ture in a 0.12 g/liter sea water solution of MS-2223 

 (tricaine methanesulfonate) and dissected in the 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Manuscript accepted October 1975. 

 FISHERY BULLETIN: VOL. 74, NO. 2, 1976. 



423 



