Macrourus

Gon, Ofer, Miya, Tshoanelo, Mcmillan, Peter & Leslie, Robin, 2021, The distributionof fourspeciesof thegenus Macrourus (Gadiformes: Macrouridae) from the Southern Ocean based on samples from the toothfish longline fishery, Zootaxa 4903 (1), pp. 105-116 : 115

Key to species of southern hemisphere Macrourus

Notes:

*Based on the material examined for this study; see Table 1 for the size range of each studied species.

*The couplets in the key use a combination of characters because single characters were mostly not useful for distinguishing the species.

*Scales series length = length of a series of 4 scale rows (or their pockets) measured below the first dorsal fin, from the centre of the lateral line scale ventrally ( Fig. 1 )

1a. Count of scales (pockets) in a diagonal row from anal fin origin up to lateral line (not including that scale) 30 or more (30–45); scale series length 11–22% HL; canal of lateral line scales below first dorsal fin flanked by low rounded ridges, that either lack or have one small spinule ( Fig. 5 a–c)...................................................................... 2

1b. Count of scales (pockets) in a diagonal row from anal fin origin up to lateral line (not including that scale) less than 30 (19–26); scale series length 17–28% HL; canal of lateral line scales below first dorsal fin flanked by steep ridges bearing strong spinules on one or both sides of the canal of each scale ( Fig. 5 d–f)..................................................... 3

2a. Pelvic-fin rays 8 (rarely 7 or 9); body scales between first dorsal fin and lateral line with median ridge bearing up to 9 spinules; scale area above and below median ridge with weak ridges sometimes bearing 1–3 spinules ( Fig. 4a, b )........... M. caml

2b. Pelvic-fin rays 9 (rarely 10); body scales between first dorsal fin and lateral line with median ridge bearing up to about 5 spinules; ridges above and below median ridge usually absent, but spineless when present ( Fig. 4c )............. M. whitsoni

3a. Underside of head with irregular series of small scales extending from below preopercle to below eye and posterior part of lower jaw ( Fig. 8e, f ); area above and below median ridge of body scales between first dorsal fin and lateral line always with spinules either singular or in smaller ridges ( Fig. 4d ); pyloric caeca 13–20............................... M. carinatus

3b. Underside of head, including area below suborbital ridge and lower jaw (excluding isthmus) scaleless, or with few scales posteriorly ( Fig. 8g, h ) (check by running a finely pointed metal object or probe along skin); area above and below median ridge of body scales between first dorsal fin and lateral line with several rounded, usually spineless ridges ( Fig. 4e, f ); pyloric caeca 9–16.................................................................................... M. holotrachys

Figures

FIGURE 1. Diagram of scale rows depicting a 4-scale series used for the ‘four scale series length’ measurement (indicated by red arrows) and a diagonal scale row counted between anal-fin origin and lateral line (adapted from McMillan et al. 2012).

FIGURE 4. Scanning electron microscope images of body scales of species of Macrourus species taken from the body area between the first dorsal fin and the lateral line. (a) and (b) M. caml SAIAB 203945, 131.2 (sample PEI15-M077) and 125.0 (sample PEI15-M085) mm HL, respectively. (c) M. whitsoni, 117.7 mm HL (sample PEI15-M088). (d) M. carinatus, SAIAB 209621, 126.9 mm HL (sample PEI15-M014). (e) and (f) M. holotrachys, SAIAB 209622, 158.2 (sample PEI15-M012) and 122.7 (sample PEI15-M013) mm HL, respectively.

FIGURE 5. Scanning electron microscope images of lateral line scales of species of Macrourus taken from below the first dorsal fin. (a) and (b) M. caml SAIAB 203945, 131.2 (tissue sample PEI15-M077) and 125.0 mm HL (tissue sample PEI15-M085) respectively. (c) M. whitsoni, 117.7 mm HL (tissue sample PEI15-M 088). (d) M. carinatus, 159.5 mm HL (tissue sample PEI15- M076). (e) and (f) M. holotrachys, SAIAB 209622, 158.2 (tissue sample PEI15-M012) and 122.7 (tissue sample PEI15-M013) mm HL, respectively.

FIGURE 8. Presence/absence of scales on underside of head in Macrourus spp. (a) M. caml, 123.1 mm HL (tissue sample PEI15- M168). (b) M. caml NMNZ P.047809, 123 mm HL. (c) M. whitsoni, 92.8 mm HL (tissue sample PEI15-M129). (d) M. whitsoni NMNZ P.036150, 137 mm HL. (e) M. carinatus, SAIAB 209621, 127.2 mm HL (tissue sample PEI15-M003). (f) M. carinatus NMNZ P.042354, 133 mm HL. (g) M. holotrachys, SAIAB 209622, 145.1 mm HL (tissue sample PEI15-M009). (h) M. holotrachys NMNZ P.039922, 166 mm HL.