Coregonus zugensis Nuesslin , 1882

Selz, Oliver M. & Seehausen, Ole, 2023, A taxonomic revision of ten whitefish species from the lakes Lucerne, Sarnen, Sempach and Zug, Switzerland, with descriptions of seven new species (Teleostei, Coregonidae), ZooKeys 1144, pp. 95-169 : 95

Coregonus zugensis Nuesslin, 1882

Figs 10 , 14

Coregonus sp. ‘Albeli’: Fatio 1885.

Coregonus sp. ‘Albeli-Albock’: Fatio 1890 (see also synonymy of C. obliterus ).

Coregonus crassirostris compactus : Fatio 1885 (see also synonymy of C. supersum ).

Coregonus lavaretus nat. riusensis, oekot. primigenius nanus: Steinmann 1950 (see also synonymy of C. muelleri and C. sarnensis ).

Coregonus macrophthalmus var. zugensis : Nüsslin 1882.

Coregonus wartmanni compactus : Fatio 1890 (see also synonymy of C. obliterus ).

Coregonus sp. ‘Zugeralbeli’: Vonlanthen et al. 2012, 2015.

Coregonus ‘Zugerseealbeli’: Steinmann 1950.

Material examined.

Syntypes. All from Switzerland, Lake Zug: Historical specimens (years 1879, 1890, 1937, 1939): MHNG-715.093, NMBE-1076263 (EAWAG-279-1, EAWAG279-2), NMBE-1076264 (EAWAG-280-1, EAWAG-280-2), NMBE-1076266 (EAWAG-282-1, EAWAG-282-2), NMBE-1076275 (EAWAG-290-2, EAWAG-290-3, EAWAG-290-3, EAWAG-290-4, EAWAG-290-5, EAWAG-290-6), N = 12, 173-236mm SL .

Diagnosis.

Coregonus zugensis is a small whitefish species with weak pigmentation of all fins and body; pale olive-brown colouration on the flanks above the lateral line; elongate slender body (body depth: 22.5-25.9% SL, mean = 24); large eye (eye diameter: 19.7-25.3% SL, mean = 22.9) with a subtle triangular eye socket (1.6-5.9% HL, mean = 3.8); many and long gill rakers (longest gill raker: 11.2-17.7% HL, mean = 14.3; total gill raker number: 33-40).

Description.

Shape: Body elongated and slender. Greatest body depth anterior of the dorsal fin. Ventral profile and dorsal profile similar and slightly arched. Dorsal and ventral profile from tip of snout to interorbital mostly straight and then slightly convex to dorsal and pelvic fin origin respectively. Head long. Snout long and tip of snout if slightly pointed resulting in a not strongly pronounced rostral plate. Mouth long and terminal. Large eye with a subtle sickle cell-shaped (seldom roundish) eye-socket. Pectoral fin long and tapered. Caudal peduncle moderately stout. Meristics: Many and long gill rakers. Colour: Pigmentation of fins and body weak in live specimens. Pectoral fin transparent and pelvic and anal fin mostly transparent. Pectoral fin very rarely pigmented at the distal part of the fin and the anal and pelvic fin rarely moderately pigmented at the median to distal parts of the fin. Dorsal, caudal and adipose fin moderately pigmented. Silvery appearance along the flanks. Dorsally above the lateral line the silvery appearance changes to a pale olive-brown. Pre-operculum and operculum with one black spot on the lower margin of the pre-operculum. Preserved specimens are brownish in colouration.

Differential diagnosis.

The differential diagnoses against the historical specimens of C. supersum from Lake Zug are given under that species account.

Coregonus zugensis - Coregonus obliterus

Coregonus zugensis can be differentiated from C. obliterus by having a wider adipose fin base (4.8-7.3% SL, mean = 6 vs. 3-5.4% SL, mean = 4.5), a smaller eye cavity (24.5-29% HL, mean = 27.4 vs. 27.9-31% HL, mean = 28.9), a longer maxilla (20.2-25.4% HL, mean = 22.9 vs. 17-21.7% HL, mean = 19.6), a shallower snout (6.6-9.2% HL, mean = 8 vs. 8-13% HL, mean = 10.1), a less wide interorbital (23.3-27.1% HL, mean = 25.3 vs. 26.4-29.7% HL, mean = 28.4) and longer and more gill rakers (middle gill raker: 10.2-15% HL, mean = 12.6 vs. 5.3-10.6% HL, mean = 7.8; longest gill raker: 11.2-17.7% HL, mean = 14.3 vs. 7.6-10.6% HL, mean = 8.8; upper arch gill raker number: 11-15, mode = 12 vs. 7-9, mode = 9; lower arch gill raker number: 21-26, mode = 22 vs. 13-18, mode= 14; total gill raker number: 33-40, mode = 35, 37 vs. 21-26, mode = 25). Based on ratios C. zugensis can be differentiated from C. obliterus by having a smaller 'eye diameter / maxilla’ ratio (EC/M: 1.11-1.34 vs. 1.38-1.65) (Tables 8 , 11 , 13 ).

Coregonus zugensis - Coregonus muelleri

Coregonus zugensis can be differentiated from C. muelleri by having a deeper caudal peduncle (6.4-8% SL, mean = 7.2 vs. 6.1-6.8% SL, mean = 6.5), a smaller eye cavity (24.5-29% HL, mean = 27.4 vs. 27-31.9% HL, mean = 29.2) and a deeper head (64.6-73.6% HL mean = 69.3 vs. 61.8-69.7% HL, mean = 65.2). Based on ratios C. zugensis can be differentiated from C. muelleri by having a smaller 'caudal peduncle depth / prepelvic length’ ratio (CD/PreP: 0.13-0.15 vs. 0.12-0.13) (Tables 6 , 8 , 11 ).

Distribution and notes on biology.

Coregonus zugensis occurred in Lake Zug and is extinct today (this is discussed in more detail in the Suppl. material 1: paragraph 4). Fatio (1885) mentions in a table three whitefish species for lake Zug ‘Balchen’, ‘Albock’, and ‘Albeli’, but later Fatio (1890) only mentions two whitefish species for Lake Zug, namely the ‘Balchen’ ( Coregonus schinzii helveticus var. zugensis ) and the ‘Albeli-Albock’ ( Coregonus wartmanni compactus ). Interestingly, Wagler (1937) noted two species to be present in Lake Zug with a remark that a third species may exist, but that its status is uncertain. Fatio (1890) does mention that fishermen have suggested that among the ‘Albeli-Albock’ there are individuals that are smaller and spawn later in the year, which they refer to as ‘Albeli’, when compared to the individuals they refer to as ‘Albock’ that are slightly larger and spawn earlier in the year. However, the specimens that Fatio (1890) could examine did not warrant this distinction and thus he suggested to group the ‘Albeli’ and ‘Albock’ under the name ‘Albeli-Albock’. Fatio (1890) suggested that the ‘Albeli-Albock’ spawn in mid-September to mid-October in Lake Zug at depths of 150-180 metres. However, with the findings that Lake Zug did harbour three species of whitefish (see the notes on biology of C. supersum and the Suppl. material 1: paragraph 4 for details) and taking into account the spawning Table in Fatio (1885) and the reports by local fishermen from that time period ( Fatio 1885, 1890) we suggest that the ‘Albeli’, C. zugensis , spawned in comparison to C. obliterus ( ‘Albock’) later in the year from mid-October to late December in deep waters of the lake. Fatio (1885) states that the ‘Albeli’, C. zugensis , spawns in the deeper parts of the lake ( ‘fond’ in French) and that the ‘Albock’, C. obliterus , spawns in even deeper waters of the lake ('grand fond’ in French). Fatio (1890) groups the ‘Albeli-Albock’ under Coregonus wartmanni compactus , which includes several other small and pelagic whitefish species from other lakes. This and the number and length of gill rakers of C. zugensis (many and long gill rakers) suggests, based on the functional properties of the number of gill rakers experimentally tested with specimens of other whitefish species from lakes Thun and Lucerne ( Lundsgaard-Hansen et al. 2013; Roesch et al. 2013), that C. zugensis was feeding predominantly on zooplankton.

Etymology.

The specific name zugensis refers to Zug, a city that gave its name to Lake Zug. An adjective.

Common name.

Zugeralbeli.

Figures

Figure 10. Coregonus zugensis, Lake Zug, Switzerland A, B syntype, MHNG- 715.093, 205 mm SL, sex unknown, preserved specimen C syntype, NMBE- 1076275 (Steinmann- 290 - 2), 188 mm SL, female, preserved specimen. Scale bars: 1 cm.

Figure 14. Illustrations of specimens of each species of Coregonus from Lake Lucerne and Sarnen. Illustrations of Lake Lucerne species are based on several individuals. Illustration of C. sarnensis is based on NMBE- 1078159, 230 mm, male. Scale bar for C. sarnensis: 1 cm.