Rhabdochona milleri Choquette, 1951

Arai, Hisao P. & Smith, John W., 2016, Guide to the Parasites of Fishes of Canada Part V: Nematoda, Zootaxa 4185 (1), pp. 1-274 : 76

Rhabdochona milleri Choquette, 1951

Description (after Choquette 1951a, and Moravec & Arai 1971). With characteristics of the genus.

Male (1 specimen): 6.94 long, 0.176 maximum width. Prostom funnel-shaped, 0.018 long, with distinct basal teeth, lined internally with longitudinal ribs forming teeth directed forwardly (exact number not determined). Vestibule including prostom 0.144, muscular oesophagus 0.300, and glandular oesophagus 1.36 long. Small, bifurcate deirids 0.063, nerve ring 0.168, and excretory pore 0.237 from anterior end. Eight pairs of subventral and one pair of [presumably lateral] pre-cloacal papillae, and six pairs of post-cloacal papillae—five pairs subventral, one pair lateral ( Fig. 48 A). Left spicule 0.402 long, with relatively blunt distal tip, and “slightly outlined” bifurcation ( Fig. 48 B). Right spicule 0.129 long, with dorsal barb at distal end ( Fig. 48 A). Length ratio of right to left spicule 1:3.12. Tail conical, 0.300 long, with sharp cuticular spike at tip.

Females (3 specimens): 10.91–12.10 long, 0.136–0.163 maximum width. Prostom funnel-shaped, 0.021–0.024 long, with distinct basal teeth, and 14 teeth projecting forwardly ( Fig. 48 C,D). Vestibule including prostom 0.111– 0.138, muscular oesophagus 0.270–0.297, and glandular oesophagus 1.59–2.35 long. Medium sized bifurcate deirids 0.063–0.081, nerve ring 0.186–0.189, and excretory pore 0.261 from anterior end. Vulva slightly postequatorial, 5.03–6.12 from posterior end. Eggs oval, 0.030–0.036 x 0.018–0.021. Surface of advanced eggs (containing larvae) smooth; poles provided with numerous fine filaments ( Fig. 48 E), those on one pole arranged mostly in parallel giving the appearance of a short ribbon-like filament with the end frayed ( Fig. 48 E, lower egg). Tail conical, 0.210–0.243 long, with sharp cuticular point.

Comment: Moravec & Arai (1971) stated that “in many important features R. milleri resembles R. ovifilamenta , and subsequent detailed studies might prove their conspecificity”.

Site: intestine

Hosts: Carpiodes cyprinus (7); Moxostoma erythrurum (2); Moxostoma macrolepidotum (1, 2, 6); Oncorhynchus

clarkii (3); Oncorhynchus mykiss (3); Prosopium coulterii (3); Prosopium williamsoni (4, 5); Rhinichthys

cataractae (4, 5); Salvelinus fontinalis (3); Salvelinus malma (3)

Distribution: Alberta, British Columbia, Ontario, Quebec

Records: 1. Choquette 1951a (QC); 2. Dechtiar 1972b (ON); 3. Mudry & Anderson 1977 (AB); 4. Anon. 1978

(BC); 5. Arai & Mudry 1983 (BC); 6. Dechtiar & Christie 1988 (ON); 7. Dechtiar & Nepszy 1988 (ON)

Figures

FIGURE 48. Rhabdochona milleri Choquette, 1951. A. male, posterior end, lateral view; B. left spicule, distal tip; C. female, en face view; D. female, anterior end; E. mature eggs. NB: scale bars were not provided in the original for either B. or C. (Redrawn from Moravec & Arai 1971)