Clarke et al Prevalence of the nematode Philometra saltatnx in the ovaries of Pomatomus saltatnx 



Jul 02 Aug 02 Sep 02 Oct 02 Apr 03 Jun 03 Jul 03 Aug 03 Sep 03 



H/lonth 



Figure 4 



Monthly intensity of live and dead Philometra saltatrix 

 in the ovaries of bluefish (Pomatomus saltatrix). 



However, a significant positive correlation was found 

 between intensity and fish weight (R= 0.169, P=0.000), 

 intensity and fork length (i?=0.221, P=0.003), and in- 

 tensity and GSI (i? = 0.262, P=0.000). The Bonferroni 

 method was applied to account for the multiple com- 

 parisons. Adjusted P-values are given. 



Observations in adult males and YOY 



Although not the target of this study, we also detected 

 the presence of Philometra saltatrix in the pericardial 

 cavity of one adult male bluefish collected in NC and 

 three adult males in NY, Fish size ranged from 411 to 

 429 mm FL. Worms were not detected in the gonads of 

 male fish. 



Additionally, we detected worms in the pericardial 

 cavity of three young of the year (YOY) bluefish caught 

 in the Long Island Sound. Fish ranged in size from 140 

 to 185 FL. 



Histopathology 



Worms found in the ovary were surrounded by oocytes 

 at various stages of development. The guts of these 

 worms were most often filled with host erythrocytes. 

 A diversity of pathological responses was noted, and 

 significant variability was found among host individuals 

 (Fig. 5). In many cases, infection was associated with 

 interstitial hemorrhage in the connective tissues of the 

 ovary. Occasionally, hemorrhage into the lumen of the 

 ovary was also observed, but it was not clear whether 

 this was caused by feeding activities of the worm or from 

 tissue damage by other means. In many cases, moderate 

 lymphocytic infiltration was observed in ovarian connec- 

 tive tissues. Some specimens showed marked edema in 



the perifollicular spaces. Prenecrotic changes, including 

 pyknosis and cellular swelling, were observed in connec- 

 tive tissue cells, and necrosis of both connective tissue 

 and oocytes (atresia) was observed in several instances. 

 Granulomatous inflammation and fibrosis occurred in 

 association with dead worms and, occasionally, atretic 

 follicles. Fibrotic capsules surrounding dead worms were 

 polylaminate and melanised and appeared to represent 

 female worms that had expelled larvae and had subse- 

 quently died. Encapsulated worms that still contained 

 larvae were also observed occasionally. 



Discussion 



Bluefish along the east coast of the United States appear 

 to be heavily infected with the ovarian nematode Philo- 

 metra saltatrix. Although many studies provide descrip- 

 tions of various philometrid species, very few provide 

 information about the prevalence, intensity, or effect 

 of these nematodes. Ramachandran (1973) described 

 the presence of several female and male worms in a 

 single ovary but provided no information on pathological 

 changes associated with infection. 



Intensity and prevalence of Philometra saltatrix cycle 

 seasonally and appear to be synchronous with the blue- 

 fish spawning cycle. Although live worms were detected 

 from April to October, the levels of infection were higher 

 in July than in any other month sampled and this tim- 

 ing is coincident with the peak of the summer spawning 

 season off NY (Chiarella and Conover, 1990). The life 

 cycle of Philometra saltatrix is unknown and, therefore, 

 it is not clear whether initial infection coincides with 

 the spawning season or if nematodes are acquired at an 

 earlier time and reside in some other host tissue site 

 before migrating to the ovaries during the spawning 

 season, perhaps stimulated by hormonal cues from the 

 host. Prevalence and intensity were much lower during 

 the spring spawning season south of Cape Hatteras, 

 NC. It is difficult to determine whether this was due 

 to geographical differences or the limited sampling that 

 month; it is possible that we missed the peak spawning 

 period in 2003. The rapid decline in both prevalence 

 and intensity after the summer spawning period indi- 

 cates that Philometra saltatrix are released or migrate 

 out of the host fish synchronously with the release of 

 fish eggs. We speculate that the reproduction cycle of 

 the nematode is closely matched to that of the host 

 bluefish. 



Other studies have reported that infection occurs af- 

 ter first host maturity and that female nematodes have 

 only been observed in the gonads of females (Oliva et 

 al., 1992; Hesp et al., 2002). Although not the focus of 

 this study, the pericardial cavity was also found to be 

 infected by Philometra saltatrix in adult males in NC 

 and NY and in YOY bluefish in NY waters, in contradic- 

 tion to these other findings. It is not clear if these YOY 

 infections represent separate infections or if they are 

 the same infections observed in adult females. Review- 

 ing the reported lifecycle of other spirurid nematodes 



