FISHERY BULLETIN: VOL. 7L NO. 2 



Figure 12. — Sirobilocephalus tnangiilaris attached in rectum of Stenella graffmani. (XI) 



a large proportion of the animals examined. 

 The history of these worms has been discussed 

 by Delyamure (1955), Dollfus (1964), Williams 

 (1968), and Dailey and Brownell (1972). P. 

 delphiiii was always found in the blubber and 

 M. grinialdii in the mesenteries. 



PARASITE LOAD RELATIVE TO 

 AGE OF HOST 



The availability of data for a large sample 

 of porpoise specimens, especially of S. graffmani, 

 dissected in relatively uniform manner pro- 

 vides an unique opportunity to examine infec- 

 tion relative to age of the host for certain of 

 the more frequently encountered parasite spe- 

 cies. We discuss only the parasite species for 

 which patterns of infestation are apparent in 

 the data. 



Spotted Porpoise, StetielLi griiffuictui 

 The sample of S. graffmani examined may be 



divided into four age classes on the basis of 

 total length, the developmental pattern cate- 

 gories defined by Perrin (1970b) and degree of 

 sexual maturity (Figure 13). Females were 

 classified as adult by the presence of corpora 

 of ovulation in the ovaries and males by 

 presence of spermatogenesis in the seminiferous 

 tubules, as determined by histological examina- 

 tion. Sixty-one of the 72 specimens were col- 

 lected during a 1-month period, and the first 

 three modes probably represent discrete repro- 

 ductive cohorts. Analysis below of parasitism 

 relative to age is in terms of the four age 

 classes, except as noted in the case of the 

 Crassicauda-\\ke nematode in the air sinuses. 

 The percent infection for Anisakis in S. 

 graffmani shows increase with age of the host 

 (Figure 14), but very large numbers of worms 

 were found only in subadults, and the parasite 

 number frequency distribution for that class 

 is obviously skewed to the right. The inference 

 to be drawn is that either some reduction in 

 number of worms occurs in a heavily infected 

 porpoise as it matures, due to the life cycle 



464 



