120 



Fishery Bulletin 104(1) 



Jul 02 Aug 02 Sep 02 Ocl 02 Apr 03 Jun 03 Jul 03 Aug 03 Sep 03 



Month 



Figure 2 



Monthly prevalence of live Philometru t^altatrix in the 

 ovaries of bluefish (Pomatomus saltatrix). Sample sizes 

 are noted on the top of the bars. 



[ZZ12002 

 IB 2003 



T " ' " I — ' — \ 



JullH Jul 24 Jul 30 Aug 5 Aug n Aug 1 7 Aug 23 Aug 29 Sep 4 



Date 



Figure 3 



Daily prevalence of live Philnmetra saltatrix in the 

 ovaries of bluefish tPomatoniuti saltatrix) in 2002 and 

 2003, 



Results 



Description and location of worm 



Philoinetra saltatrix was identified in the gonads of 

 female fish ranging in size from 363 to 815 mm (FL) in 

 both NC and NY samples. The majority of worms found 

 in the ovaries were gravid females. Gravid female worms 

 were visible macroscopically and most often visible even 

 before the initiation of ovary dissection. Female worms 

 reached a maximum of 150 mm in length and approxi- 

 mately 300 iim in width. Dead worms were present in 

 all months sampled and were encapsulated by several 

 melanised layers of fibrotic tissue. Approximately 20 

 juvenile male and female worms were identified in the 

 ovary of a female fish in July 2003. These immature 

 worms reached a maximum length of 2 mm. It should 

 be noted, however, that not all fish were examined 

 microscopically; therefore, it is possible that other male 

 and juvenile worms were present in other hosts but not 

 detected. 



Prevalence and intensity 



Bluefish in the western North Atlantic represent a 

 single genetic stock (Graves et al., 1992), allowing us 

 to combine data from New York and North Carolina to 

 examine seasonal trends. Pooled by month of capture, 

 the prevalence of infection varied seasonally during the 

 two sampling years. In NC, prevalence of live nematodes 

 was 7% in April, the spring spawning season (Fig. 2). 

 Prevalence of live worms in NY in June was 4.8% and 

 reached a maximum of 79% (2002) and 42% (2003) in 

 July during the summer spawning season (Fig. 2). It is 

 important to note that sampling in 2002 did not begin 



until mid-July but was conducted for the entire month 

 in 2003. If only the second half of July is examined for 

 both years, the prevalence is 79% and 83% for 2002 and 

 2003, respectively. This peak in prevalence was followed 

 by a slow decrease in live worms until late August and 

 early September after which time live worms were no 

 longer detected. 



Examination of prevalence by sampling day showed 

 greater evidence of interannual variation. In the middle 

 of July 2002, 100% of bluefish examined were infected 

 with live Philometra saltatrix, whereas in 2003 the 

 highest percentage of fish sampled that were infected 

 was 91% (Fig. 3). Furthermore, in 2002 prevalence 

 peaked in the middle of July, whereas in 2003 preva- 

 lence was highest at the end of the month. Additionally, 

 live worms were detected until the end of August in 

 2002 but were detected two weeks later in 2003. 



Intensity of parasite infection, as indicated by total 

 live and dead worm weight per fish, reached a maxi- 

 mum 0.145 g (mean of 0.081 g ±0.1367) and was high- 

 est during the month of July in both years of the study 

 (Fig. 4). Patterns of intensity were similar to those of 

 prevalence; intensity was highest during the summer 

 spawning season and then later decreased. One bluefish 

 caught just south of Cape Hatteras, NC, in the begin- 

 ning of May 2003 had the highest intensity observed 

 with over 100 nematodes present (Fig. 5, A and B). This 

 fish was not included in the data analysis because it 

 was the only fish examined during that month, but this 

 extreme instance of infection sets the upper bound on 

 the level of observed intensity. 



Binary logistic regression was used to test whether 

 the presence or absence of the nematode was related 

 to fork length (P=0.096), fish weight (P=0.292), or GSI 

 (P=0.783), but no significant relationships were found. 



