FISHERY BULLETIN: VOL. 74, NO. 2 



17°C for spot), because Peters et al. (1974) showed 

 that evacuation rate of juvenile pinfish and spot 

 is related directly to temperature. 



Feeding Periodicity and Feeding Rate 



Observations of larval gut contents through 24 

 h again indicated that these larval fish contained 

 the greatest amount of food during daylight hours 

 (Figure 2). Peaks in gut contents for both pinfish 

 and spot were at 1200 h. Water temperature was 

 15°C. 



The periodicity observed in the gut contents 

 does not represent the actual feeding periodicity. 

 However, if our evacuation data and model are 

 appropriate, the feeding periodicity may be calcu- 

 lated from the periodicity of gut contents. Gut 

 contents at the beginning and end of each sam- 

 pling interval (Figure 2 ) differ by an amount equal 

 to the amount consumed minus the amount 

 evacuated during that time period (Peters and 

 Kjelson 1975). Thus, we can add the amount 

 evacuated in each interval from the change in gut 

 content to achieve the amount ingested during 

 the interval. Maximum hourly feeding rates 

 (from the 1000-1200-h sampling interval) were 26 

 copepods/h for pinfish and 17 copepods/h for spot. 



Daily Rations 



Estimates of daily ration for pinfish and spot 

 larvae were higher than those obtained from the 

 1972-73 study. During our earlier study, pinfish 

 ate 38 copepods/day while the present estimate 

 indicates 92. Previous estimates for spot were 47 

 and 99 copepods/day while our present estimate is 

 115 (Table 5). The increased ration sizes are at- 

 tributed to the use of higher instantaeous evac- 

 uation rates, and in the case of pinfish, to the 

 presence of greater amounts of food during the 

 feeding periodicity study (Figure 2). Pinfish di- 



oeoo 1200 



1600 2000 



TIME Of DAY 



Figure 2. — Diel cycle of digestive tract contents in larval pin- 

 fish and spot at 15°C based upon the geometric mean of 

 the number of copepods per fish (n = 10 fish per sampling 

 time). Vertical bars are equal to two standard errors. 



gestive tracts had an average of 47 copepods/fish 

 at 1200 h during the 1974 sample day whereas 

 during 1972 they only had 10 copepods/fish. Spot 

 gut contents at 1200 h averaged 17, 37, and 27, 

 respectively in the three successive years of the 

 study. 



Based on our daily ration estimates of 1.3 and 

 2.0 cal/fish per day (Table 5) and the mean 

 weights of the larvae, this was equal to a con- 

 sumption rate of approximately 0.05 cal/mg fish 

 wet weight per day for both species. The similar- 

 ity is interesting since the average pinfish weight 

 was only 60% that of spot and suggests that lar- 

 vae of dissimilar species and sizes have similar 

 consumption on a unit weight basis. Oxygen con- 

 sumption measurements by D. E. Hoss (pers. 

 commun., Atlantic Estuarine Fisheries Center, 

 Beaufort, N.C.) indicate that similar respiration 



Table 5. — Daily rations calculated fi-om feeding studies and O2 consumption mea- 

 surements at 15°C for larval pinfish and spot in the Newport River estuary, N.C. 



'3.38 cal/mg O2. 



^Pinfish data from Hoss (1974), spot data from D. E. Hoss (pers. commun , Atlantic Estuarine Fisheries 

 Center, Beaufort, N.C). 



^Pinfish data from W. F. Hettler, Jr. (pers. commun., Atlantic Estuarine Fisheries Center, Beaufort, N.C), 

 spot data from Hoss et al. (1974). 



430 



